Alusil cylinder block DIY reconditioning

[ZimbutheMonkey]

Not sure if this information has made it on to this forum so I wanted to post it.

If you are doing a teardown on an Alusil block that has oil consumption issues, it looks as though you can recondition the block yourself for around $1000 ($150 in materials and $850 for rings).

Here's what you need:

https://www.goodson.com/search.php?mode=search&page=1&keep_https=yes


By way of summary; Alusil blocks use a combination of Aluminium and Silicone which is suspended evenly throughout the entire casting assembly (i.e. it's NOT a cylinder liner)

The honing process removes a few microns worth of Aluminium, exposing the harder Silicone particles which create a porous and hard surface which retains an oil barrier for the piston rings to slide against.

So long as there is no significant scoring, you can use a drill at 150 RPM with the Sunnen felt pads and paste. You hone the bore for about 90 seconds until a dull, matte finish with a faint cross-hatch is obtained.

From what I can see, the paste contains silica, suspended in an elastopolymer. During the honing process, pressure against the cylinder wall should be kept to a minimum. This, combined with the silica being suspended in a medium which cushions the silica particles as they sweep against the honing surface is what makes the porosity uniform and the exposed silicone particles smooth enough as to not damage the rings during break-in.

Have a read through this thread, the latter 2/3 of the thread explains the process very well.

http://rennlist.com/forums/928-forum/368216-preparing-restoring-alusil-bores-for-dummies-2.html

Bottom line, if you have an oil consuming engine torn down for something like valvetrain servicing and want to take the extra step of disassembling the bottom end, it may be worth the time and effort to hone and re-ring the block. The materials to do it aren't overly expensive (vs a used block that may or may not work any better) and it appears to be quite straightforward to do a re-hone.

If I ever pull my engine for a valvetrain service, I think I'll give it a shot. I'll post up results if I ever get around to it (knock on wood, hopefully later, rather than sooner [:p]

Hope this helps [up]

[aroderick56]

We have been honing the alusil blocks in the 944's , dont see why we can't on these blocks

[chain_slappins4]

but can you get oversize pistons that aren't a fortune on the 4.2?

Sent from the S4 with a Tap!!!

[aroderick56]

no, not enough material to bore for oversize pistons

[chain_slappins4]

so then honing isn't going to fix scored walls.. UNLESS the scoring is minor

Sent from the S4 with a Tap!!!

[chain_slappins4]

pretty silly to have a one time use block... can these blocks be sleeved?

Sent from the S4 with a Tap!!!

[aroderick56]

honing isn't for fixing cylinder wall scoring, so this will only work with cylinders without significant scoring. It will remove small marks but not much else

[aroderick56]

pretty silly to have a one time use block... can these blocks be sleeved?

Sent from the S4 with a Tap!!!

yes but its not cheap and not easy to do

[chain_slappins4]

so then getting a block with any type of compression loss due to scoring in hopes of fixing it is a waste of money

Sent from the S4 with a Tap!!!

[aroderick56]

all depends on what you consider a waste of money, i plan on sleeving my block in the future

[pwest15]

I believe it's possible to actually fix more than minor scoring by doing a nikasil coating treatment. I believe the coat the whole cylinder with nikasil, then hone everything away, a bit past oem tolerances just so all the scores are filled, and then they recoat and hone back to oem diameter. The nikasil which will hold up better than alusil as well and can possibly be an alternative to sleeving although I don't think you could push it quite as far. I know that a few shops were willing to perform this treatment on a BHF 4.2 block but their names have escaped me because I wasn't the individual who got in touch. I believe one is in Indiana and they charge something like $1200 but that's all I know haha

[aroderick56]

Just to add to pwest15, sleeving will be able to make more horsepower and be way more dependable

We do quite a bit of Porsche blocks for the road racing guys, both with nikasil and alusil but those guys are stock n/a just looking for a freshen

[chain_slappins4]

Just to add to pwest15, sleeving will be able to make more horsepower and be way more dependable

We do quite a bit of Porsche blocks for the road racing guys, both with nikasil and alusil but those guys are stock n/a just looking for a freshen
so then how much work is it to sleeve these BHF blocks? and how expensive?

Sent from the S4 with a Tap!!!

[jr1415us]

See this thread/ argument about the realities of sleeving the 4.2l motor: http://www.audizine.com/forum/showthread.php/690728-Sleeving-a-S4-4-2?highlight=sleeving

[ZimbutheMonkey]

honing isn't for fixing cylinder wall scoring, so this will only work with cylinders without significant scoring. It will remove small marks but not much else

I can't say for certain how deep the scoring needs to be in order to render the block useless. However, it wouldn't surprise me if a good chunk of the oil consumption/compression loss that occurs in these engines is the result of a bunch of minor (even microscopic) scoring on the walls.

If this is the case, it may well be worth doing it, even if you can't remove all the scoring. If you can at least repair the bulk of the damaged sealing surface area, I;ll bet you could regain a good portion of lost compression and significantly mitigate future oil consumption.

The scoring/compression loss issues on our engines can't be that much different from the Porsche ones, and they seem to be getting good results with this treatment.

I mean, for the minimal cost of materials, why not give it a shot, it's a hell of a lot cheaper than rolling the dice on a used engine that may suffer from the exact same issue and as others have mentioned, sleeving these engines seems to be an expensive crap shoot at best (if it can even be reliably done at all).

[q_dubz]

Good info

[ZimbutheMonkey]

Good info

thanks [up]

Maybe this has been discussed and I just missed it, but the impression I get is that people just seem to throw their hands up in the air and give up when it comes to oil consumption and compression loss.

It kinda surprises me that more people aren't doing this (or then again, maybe it shouldn't....) but it seems that re-honing has been a pretty common practice for some time in the Porsche community.

EDIT: there appears to be at least one thread on the subject on AZ http://www.audizine.com/forum/showthread.php/518239-2004-s4-engine-honing

However, no one seems to have actually reported back on whether or not it succeeded.

As well, the ring sets aren't cheap by the looks of it (about $800).

Still, as long as there weren't a ton of deep gouges in all the cylinders, I'd sooner bet my $1000 on a rehone and re-ring vs a used block, even if there was some minor scoring left afterwards.

My thought is that even if you have a little residual scoring, having the proper porosity on the rest of the cylinder would likely allow for enough oil to be carried to regain you most of your compression.

[aroderick56]

i think alot of that has to do with people not having the experience or patience to figure it out. its very common with the porsche's, it could become more common with these engines. I think there is a huge disconnect because people are able to buy these cars inexpensively but dont/cant spend the money to pay repair bills.

[ZimbutheMonkey]

i think alot of that has to do with people not having the experience or patience to figure it out. its very common with the porsche's, it could become more common with these engines. I think there is a huge disconnect because people are able to buy these cars inexpensively but dont/cant spend the money to pay repair bills.

You make a good point, I guess I never viewed these cars as being cheap to buy.

That being said, there are a lot of people who have likely spent at least $2000-4000 to buy a used engine, and that's not chump change (at least in my books lol).

Also, since you seem to have some knowledge of the procedure, care to have a quick re-read of my post (I added an edit) and weigh in on the last part (re: the rehone restoring a good portion of the compression even if there was still some residual scoring afterwards?)

[q_dubz]

Yea I figured this out years ago before even owned the car. I've known plenty of Porsche owners over the years and have a few industry contacts who filled me in as well.

I'm not sure why there is this doomsday stigma about this engine. It's nothing special but people don't care to learn or at least conduct a little critical thinking on their own.

What follows is regurgitation of imperfect info from other sources that gets even more misconstrued over time.


Anyway, sleeving and nikulsil coating both with run about the same cost in the end..... Expensive lol.

[ZimbutheMonkey]

Yea I figured this out years ago before even owned the car. I've known plenty of Porsche owners over the years and have a few industry contacts who filled me in as well.

I'm not sure why there is this doomsday stigma about this engine. It's nothing special but people don't care to learn or at least conduct a little critical thinking on their own.

What follows is regurgitation of imperfect info from other sources that gets even more misconstrued over time.

well said.....

What really surprises me (given the value of their vehicles and engines) is that no one in the RS4 community has tried this. (then again, I guess your point above probably applies even more to that crowd lol).

Also, from what I've seen, Nikasil is also prone to damage if there is any hint of Sulfur in your fuel. Probably not a big issue in North America, but still, it's definitely a drawback of the procedure.

[SprintBlueWorld]

Let the experiment be made.

You could be a Hero to folks with this problem, and or a villan at the same time, to those who threw away their cars due to it. You have to consider though it's a lot of work just to be able to access the cylinders then button back up reinstall and test. Many wouldn't even try, and just part their car out. Many who do try have already made up their minds to throw money at it and not "scimp" out or risk the same or another sort of failure by trying to save money somewhere.

I still don't understand why no one has engineered metal guides for our cars. Are thry really that complex that a 3d printer couldn't replicate?

[emcaha]

I still don't understand why no one has engineered metal guides for our cars. Are thry really that complex that a 3d printer couldn't replicate?

It's not the complexity but the physical property requirements which would negate a 3D printer application. You'd also have to have a set of new guides to generate a solid model to use as the "master" for duplicating. There's been a few previous threads around the idea of making your own replacement guides and the application isn't very cost effective with such a small demand. This thought process is exaggerated with the idea of making your own plastic replacement guides.

The only real solution would be to get a set CnC'd but you're talking manufacturing on a one-off scale which again, isn't very cost effective. In general I think the same thought process as this thread's sleeving question would apply. With enough time and money anything is doable but is it a reasonable alternative.

[chain_slappins4]

It's not the complexity but the physical property requirements which would negate a 3D printer application. You'd also have to have a set of new guides to generate a solid model to use as the "master" for duplicating. There's been a few previous threads around the idea of making your own replacement guides and the application isn't very cost effective with such a small demand. This thought process is exaggerated with the idea of making your own plastic replacement guides.

The only real solution would be to get a set CnC'd but you're talking manufacturing on a one-off scale which again, isn't very cost effective. In general I think the same thought process as this thread's sleeving question would apply.
I was discussing with another member here about making all the guides out of steel or forged aluminum, even if just for myself. I think if I could get my hands on a clean set, blueprint it, then I could modify it, and essentially take that weak link out of the equation. the other members seems to think it would be dangerous given the fact that steel or aluminum does not give, but if it's designed correctly, or redesigned better, you don't need to worry about give.. just would need to do an analysis to see which material would be best suited to this application.

Sent from the S4 with a Tap!!!

[aroderick56]

You make a good point, I guess I never viewed these cars as being cheap to buy.

That being said, there are a lot of people who have likely spent at least $2000-4000 to buy a used engine, and that's not chump change (at least in my books lol).

Also, since you seem to have some knowledge of the procedure, care to have a quick re-read of my post (I added an edit) and weigh in on the last part (re: the rehone restoring a good portion of the compression even if there was still some residual scoring afterwards?)

Even if there was some scoring leftover, a fresh hone/pasting could provide better compression results. It is all very dependent on conditions

edit: I did discuss this with Dean about trying it on my block while it was all out. We decided, at least for myself, that it would be best to sleeve my spare block instead because of the ultimate power goal I want. More power and more durability

[aroderick56]

JHM timing kits already take out the weak links of the timing system, no need to try and engineer new guides.

[chain_slappins4]

JHM timing kits already take out the weak links of the timing system, no need to try and engineer new guides.
but the JHM timing kits still use plastic parts, correct? when you mix plastic with chains moving at what ever speed, and plus you have a metal cam that moves these plastic guides in and out, flexing the plastic back and forth how ever many cycles, nah.. I'd rather make them out of something a bit more durable then plastic.. it'll cost me nothing more then my time and material. I have the equipment to make it, already spent the money on education, and my family owns a machine shop.. besides, I love a good challenge...

Sent from the S4 with a Tap!!!

[Hooblah]

Is there no other coating that can be applied to the block other than alusil/nikasil? It's been almost 15 years since the first S4 was produced, surely there must be some new tech in that time? I remember nikasil going back to the 90s. In fact I've just googled it and wikipedia says nikasil was developed by Mahle in 1967. Near enough 50 years ago!

And what about coating the pistons and rings instead of the cylinders with coatings such as Nitron CA and Diamolith DLC?

Another approach could be oversize pistons. What's that likely to cost versus getting it recoated?

Here's an interesting article:
http://www.mmsonline.com/articles/automotive-cylinder-coating-for-high-production-applications

[chain_slappins4]

Is there no other coating that can be applied to the block other than alusil/nikasil? It's been almost 15 years since the first S4 was produced, surely there must be some new tech in that time? I remember nikasil going back to the 90s. In fact I've just googled it and wikipedia says nikasil was developed by Mahle in 1967. Near enough 50 years ago!

And what about coating the pistons and rings instead of the cylinders with coatings such as Nitron CA and Diamolith DLC?

Another approach could be oversize pistons. What's that likely to cost versus getting it recoated?

Here's an interesting article:
http://www.mmsonline.com/articles/automotive-cylinder-coating-for-high-production-applications
further up its been said that there really isn't enough material for a bore and oversize pistons, I thought that would be an option also.. but looks like that one is a no go

Sent from the S4 with a Tap!!!

[ZimbutheMonkey]

Is there no other coating that can be applied to the block other than alusil/nikasil? It's been almost 15 years since the first S4 was produced, surely there must be some new tech in that time? I remember nikasil going back to the 90s. In fact I've just googled it and wikipedia says nikasil was developed by Mahle in 1967. Near enough 50 years ago!

And what about coating the pistons and rings instead of the cylinders with coatings such as Nitron CA and Diamolith DLC?

Another approach could be oversize pistons. What's that likely to cost versus getting it recoated?

Here's an interesting article:
http://www.mmsonline.com/articles/automotive-cylinder-coating-for-high-production-applications

Technically, Alusil isn't a coating, the entire block casting is the same material throughout. After reading up on it and giving it some thought, I've actually realized that it's probably the best way of making an Aluminium block as it can technically be bored oversize and re-honed just like cast Iron.

Where the problem lies is that in order to shoehorn the block into the B6 frame, Audi made the space between the cylinder walls paper thin. If there was another 3-5 mm of material, you could just re-bore a severely scored block it, get it re-honed and put a set of oversized pistons in.

[Hooblah]

Hmm. Just how badly do the cylinders get scored? I can't see it being and deeper than 1mm, even 1mm is pushing it. And what exactly causes the scoring in the first place?

[emcaha]

I was discussing with another member here about making all the guides out of steel or forged aluminum, even if just for myself. I think if I could get my hands on a clean set, blueprint it, then I could modify it, and essentially take that weak link out of the equation. the other members seems to think it would be dangerous given the fact that steel or aluminum does not give, but if it's designed correctly, or redesigned better, you don't need to worry about give.. just would need to do an analysis to see which material would be best suited to this application.

"but the JHM timing kits still use plastic parts, correct? when you mix plastic with chains moving at what ever speed, and plus you have a metal cam that moves these plastic guides in and out, flexing the plastic back and forth how ever many cycles, nah.. I'd rather make them out of something a bit more durable then plastic.. it'll cost me nothing more then my time and material. I have the equipment to make it, already spent the money on education, and my family owns a machine shop.. besides, I love a good challenge...


Sent from the S4 with a Tap!!!

Yes, the JHM kit uses the OEM plastic components except the one updated RS4 metal guide. I agree if you have the means to do something like this easily then go for it. Have a machine shop at the place I work at as well and have built a few small pieces instead of buying before but nothing I deem as a critical component. A big factor in material selection is going to be the different hardnesses of interacting parts and what will inevitably become the "wear" item. Making the guides out of a harder material such as steel could transfer the wear to the chain itself which could becomes just as (if not more) detrimental. The same thought process would be applicable to the cams actuating the guides, more weight of guides or more required pressure from metal on metal could cause the cams themselves to fail.

Not knocking your thought process at all but it's definitely something to consider. Honestly, can't believe I'm even sounding like I'm defending the plastic guides but in the grand scheme of things if I had to choose a wear item out of the timing system, I think the guides are the proper choice (and I'd be willing to bet Audi had a similar thought process). It's inevitable that parts are going to wear, trying to figure out what the wear item will be or how to tailor it to the part you want to wear is the challenge.

I'd really like to see metal guides with possibly a plastic wear plate for the chains to ride on. Think there is a few components of the timing system which have this. That way if the wear plate was to fail/break you'd have the metal guide to fall back on and keep enough tension on the chain so you won't skip timing.

My .02 on the matter.

[q_dubz]

Let's be clear here. The guides will still wear. They are plastic covered. Otherwise it would be bad. They are NOT supposed to break.

[chain_slappins4]

Yes, the JHM kit uses the OEM plastic components except the one updated RS4 metal guide. I agree if you have the means to do something like this easily then go for it. Have a machine shop at the place I work at as well and have built a few small pieces instead of buying before but nothing I deem as a critical component. A big factor in material selection is going to be the different hardnesses of interacting parts and what will inevitably become the "wear" item. Making the guides out of a harder material such as steel could transfer the wear to the chain itself which could becomes just as (if not more) detrimental. The same thought process would be applicable to the cams actuating the guides, more weight of guides or more required pressure from metal on metal could cause the cams themselves to fail.

Not knocking your thought process at all but it's definitely something to consider. Honestly, can't believe I'm even sounding like I'm defending the plastic guides but in the grand scheme of things if I had to choose a wear item out of the timing system, I think the guides are the proper choice (and I'd be willing to bet Audi had a similar thought process). It's inevitable that parts are going to wear, trying to figure out what the wear item will be or how to tailor it to the part you want to wear is the challenge.

I'd really like to see metal guides with possibly a plastic wear plate for the chains to ride on. Think there is a few components of the timing system which have this. That way if the wear plate was to fail/break you'd have the metal guide to fall back on and keep enough tension on the chain so you won't skip timing.

My .02 on the matter.
that was another option I was looking at, but how to reliably fasten/attach the Delrin to the steel core... if they made these parts like this for the RS, is there maybe a way to modify it to fit the BHF blocks?

Sent from the S4 with a Tap!!!

[chain_slappins4]

Let's be clear here. The guides will still wear. They are plastic covered. Otherwise it would be bad. They are NOT supposed to break.
yes they will. anytime you have steel moving over plastic, the end result will be the softer material being worn away. on the issue of breaking... maybe a better idea would be to reinforce the plastic guides with steel or aluminum inserts around the known breaking points..

Sent from the S4 with a Tap!!!

[emcaha]

Let's be clear here. The guides will still wear. They are plastic covered. Otherwise it would be bad. They are NOT supposed to break.

100%. I am in no way defending or trying to justify the breaking of guides or the plastic guides themselves. And yes, the guides will still wear. It's a question of if other parts will begin to wear more with a change of materials.

Chain Sappin: You'd have to figure out some type of snap feature or something similar to not have to rely on screws, bolts, adhesive, etc. Ideally you'd overmold the plastic onto the guide and add some internal retention features but not very applicable in a one-off. The plastic on top of metal timing components I was referring to are in BHF engine already.

[q_dubz]

yes they will. anytime you have steel moving over plastic, the end result will be the softer material being worn away. on the issue of breaking... maybe a better idea would be to reinforce the plastic guides with steel or aluminum inserts around the known breaking points..

Sent from the S4 with a Tap!!!

that's exactly what the updated RS4 ones are...

[chain_slappins4]

that's exactly what the updated RS4 ones are...

only in the RS4 ones.. correct?

[q_dubz]

They swap over to s4

[chain_slappins4]

well shit.. then there is no need for any more talk on that subject

Sent from the S4 with a Tap!!!

[chain_slappins4]

I'm still learning about these motors, so you'll have to forgive my ignorance in regards to them, but if someone would have just said that earlier... I wouldn't have wasted mine or anyone else's time about these stupid guides

Sent from the S4 with a Tap!!!

[josh_avant]

On the resurfacing front, I wonder if Plasma Transferred Wire Arc resurfacing is / will ever be a reasonable option for BHFs? Definitely not an area that I know much, but from a naive high level it seems like a good fit.

[chain_slappins4]

what about hard chroming the cylinder walls?

edit... the rings would never seat... NM

Sent from the S4 with a Tap!!!

[2004B6S4]

I'm still learning about these motors, so you'll have to forgive my ignorance in regards to them, but if someone would have just said that earlier... I wouldn't have wasted mine or anyone else's time about these stupid guides

Sent from the S4 with a Tap!!!


There is only 1 metal guide that swaps over from the rs4. the s4 already has a couple metal guides from the factory, the problem is that there are several others that are all plastic. only 1 of the all-plastic guides can be replaced with a metal one from the rs4, but there are still others and they will break eventually.

[chain_slappins4]

There is only 1 metal guide that swaps over from the rs4. the s4 already has a couple metal guides from the factory, the problem is that there are several others that are all plastic. only 1 of the all-plastic guides can be replaced with a metal one from the rs4, but there are still others and they will break eventually.
so then what are all these "updated" guides that everyone is taking about?

Sent from the S4 with a Tap!!!

[q_dubz]

Gents start a separate topic about valve guides please.

[emilio]

yes, to get this back on track...

i'm pretty skeptical of this for reducing oil consumption. one, the scoring would have to be deep enough to be a problem, yet shallow enough to not need oversized rings. it's a shot in the dark since no one seems to know any actual dimensions for how deep their scoring is, let alone how it relates to consumption. two, i cringe a little at doing precision high-compression bore honing with the intent to remove significant material just using a hand drill. i would really want something to ensure alignment to the block.

- emilio

[ZimbutheMonkey]

yes, to get this back on track...

i'm pretty skeptical of this for reducing oil consumption. one, the scoring would have to be deep enough to be a problem, yet shallow enough to not need oversized rings. it's a shot in the dark since no one seems to know any actual dimensions for how deep their scoring is, let alone how it relates to consumption. two, i cringe a little at doing precision high-compression bore honing with the intent to remove significant material just using a hand drill. i would really want something to ensure alignment to the block.

- emilio

As far as I can tell, as long as you can't catch your fingernail on the scoring, then the hone will make a difference on those areas.

However, even if you had a few deep gouges, re's bound to be some more minor ones that the hone will still take out which ought to help compression. In addition to that, it will refresh the remainder of the bore which, as most sliding surfaces, will have likely had some wear over time.

The other assumption that people seem to make (which I disagree with to some extent) is that the oil consumption on a block with mild scoring is all due to the scoring itself. That assumption ignores the possibility that the remainder of the bore has also been worn (due to the same conditions that resulted in the scoring) and is contributing to the oil consumption.

Put otherwise, let's say you have an oil consuming/low compression bore that has a few gouges that a hone won't take out. While a hone won't restore 100% of the ring seal. There's a good chance that a hone and re-ring will restore a significant portion of the lost seal. Yes, you'll still have a tiny bit of compression leak past the deeper gouges, but if you could restore the bulk of the compression for $1000, it's a much better alternative than having to source a used block that may have more unseen wear (i.e. worn bore and rings) than a lightly scored block with a refinished bore and new rings.

Finally, I wouldn't be to concerned about alignment to the block (i.e needing a machine). If you have a look at the technical documents, you're not taking any significant portion of the material out, it's literally just removing about a hundred microns worth of material. As long as you're not completely careless with your hone, you'll be fine. As the threads I linked to indicate, Porsche guys have been doing this themselves for a while and haven't ran into issues.

[q_dubz]

^^^^thank you! Drives me nuts people think that.

[Sphawkins007]

So could you expect an improvement from just replacing the rings and doing nothing else?

[q_dubz]

So could you expect an improvement from just replacing the rings and doing nothing else?

i would say no. You need the silicon exposed to wear the rings.

[ZimbutheMonkey]

So could you expect an improvement from just replacing the rings and doing nothing else?

Agreed with Q-Dubz. That said, why not do the hone? It's only $150 of materials.

Plus, if you read the literature, apparently, the honing process is essentially self limiting in terms of how much material gets taken out.

Not to say that you can't mess it up, but just follow the directions, 150 rpm speed, the lightest pressure you can put against the bore and go up and down with the hone for 90 seconds per bore until you get a dull matte finish. Doesn't get much more straightforward than that...

[neilpaku]

I'm going to hone and re-ring mine. But before I do, I was curious if anyone had first-hand experience with the technique that a Porsche owner had where he just cleaned the cylinders with dishwashing liquid and re-ringed. He did not hone. I think it was implied that he went from burning oil to not burning much oil and/or improved compression. I don't really want to pull the whole block apart just for a quick hone although I guess at this stage, the only moving part left would be the crank...

[q_dubz]

Best to do it right the first time and hone it. You have to pull the pistons anyway. Just cover the crank journals and get it done. Then spray it down with starter fluid or brake clean. I've done many engines this way.

[IslandHydro]

I'd like to hear the folks at JHM chime in on this discussion (honing / rings)? Have you guys tried this? Anything to add to the discussion?

[Hooblah]

What exactly causes the bore scoring?

[q_dubz]

What exactly causes the bore scoring?

Carbon buildup on the ring lands supposedly from a faulty PCV letting oil in that eventually seeps down into the cylinders. A routine oil treatment *should* mitigate this.

[SprintBlueWorld]

I recently heard it said Audi hasn't made a proper PCV. When I did my intake spacers I replaced the OEM with an aftermarket PCV. I think Slow4 also suggested bad air filtration in his Hello thread.

[2004B6S4]

What exactly causes the bore scoring?

I've heard multiple theories on that including excess heat from the precats, and pushing the engine too hard before warmup, and now the 2 suggestions above which are both new to me. None of those theories seem any more credible or verifiable than the others, to me. I wish there was a more definitive answer to that question because I'd love to know what it is!

[pwest15]

I've heard multiple theories on that including excess heat from the precats, and pushing the engine too hard before warmup, and now the 2 suggestions above which are both new to me. None of those theories seem any more credible or verifiable than the others, to me. I wish there was a more definitive answer to that question because I'd love to know what it is!

I understand that it might not be convenient to just have one problem going on in the motor caused by one thing that could have a single solution but the fact of the matter is that these are exceedingly complex pieces of engineering and unfortunately, there are some complex faults in a design here or a material there.

However, the easiest thing to do is look at someone who's gotten their motor in this car to a very high mileage and still seems content. What have they done? Well they probably do very regular oil changes, they've probably changed the pcv once or twice because it's cheap and easy, they've almost certainly replaced at least the single plastic guide timing system in the motor that is known to crack, they might have gutted precats or some other form of aftermarket exhaust, and they probably take it real easy on the car before they decide to romp on it. If you noticed, these are direct solutions to some possible listed causes that people have come up with for the cylinder scoring problem. I'm not saying it's all of them but I'm also not saying that these aren't impossible to do. What I'm trying to say is that it doesn't matter if the theories are credible or directly verifiable so long as they're relatively sensible and people who are getting more life out of their motors are utilizing the solutions as well.

[komseh]

I recently heard it said Audi hasn't made a proper PCV. When I did my intake spacers I replaced the OEM with an aftermarket PCV. I think Slow4 also suggested bad air filtration in his Hello thread.

What aftermarket unit did you go with?

[neilpaku]

I decided to deglaze and "expose" it, as the Sunnen guide says. The Porsche owners appear to give a quick deglaze with a Scotchbrite attached to the 3-finger hand-held hone, then expose with the Sunnen AN-30 paste. There's apparently a new Sunnen stone kit that supercedes the AN-30 technique but I'm going to stick with the AN-30 paste as it appears forgiving of shade-tree use.
Another question that might seem silly to some but it's worth some (constructive) feedback. I'm curious on folks' thoughts on whether to the replace the rings. Reason I ask is the following:
- those rings are very hard and I've seen some mention that there's really not a lot of wear, even when the bores are worn.
- oil consumption seems to depend more on the condition of the bore than the rings (assuming the rings are not broken or stuck with carbon/gum)
- they are already bedded in, admittedly on what will be a different surface at least to begin with. Assuming they're not worn and the gap hasn't changed out of spec, what measurable benefit would come from replacing them. Some folks have gone the route of honing and new rings and have not been successful in having them bed in. Could be many variables of course...
Before anyone flames, if there is some intelligent insight, I'm all ears : )
In any case, I'll pull them out, clean them, and then measure the gap. Would someone have the gap range for (I assume) OEM rings?

[emilio]

The other assumption that people seem to make (which I disagree with to some extent) is that the oil consumption on a block with mild scoring is all due to the scoring itself. That assumption ignores the possibility that the remainder of the bore has also been worn (due to the same conditions that resulted in the scoring) and is contributing to the oil consumption.

Put otherwise, let's say you have an oil consuming/low compression bore that has a few gouges that a hone won't take out. While a hone won't restore 100% of the ring seal. There's a good chance that a hone and re-ring will restore a significant portion of the lost seal. Yes, you'll still have a tiny bit of compression leak past the deeper gouges, but if you could restore the bulk of the compression for $1000, it's a much better alternative than having to source a used block that may have more unseen wear (i.e. worn bore and rings) than a lightly scored block with a refinished bore and new rings.

yes, i think the exact mechanism of oil loss and cylinder wall scoring is not well understood. if Audi knows, they aren't telling.

it's my understanding of the Alusil process that leaves me skeptical that a single-step process could do anything significant, especially without new rings (or even oversized ones). note that the OP's Porsche forum link is for a guy that also put new rings in. it may just be the rings that really fixed his compression issues, while the honing was just proper prep for new rings.

from what i've read (Sunnen docs, Porsche forums) making an Alusil block is a three-step process:


bore the cylinder as normal
hone with a compound that just removes aluminum, leaving microscopically sharp silicon (oxide? carbide?) sticking out of the cylinder wall and creating a gap for oil to dwell
hone the silicon crystals so they form nodular profiles, smoothing their surface for piston rings to glide over


any cylinder scoring will be removing both aluminum and silicon from the walls, creating a microscopically out-of-round cylinder. removing those without keeping the rest of the cylinder round may be beyond the ability of existing (or new) rings to fill. the one saving grace is that the final Alusil step is with a silicon grinding compound, which will definitely remove the aluminum as well. so, if your cylinder walls happen to be within a pretty narrow range of scoring depth and piston ring wear then you might be able to improve the conditions without new piston rings by keeping the whole thing round (i.e. pushing the cylinder walls back to the depth of the scoring).

i would be very happy if this worked for someone with well-documented oil consumption, because i might consider doing it, too (1qt/1000mi for me). i'm not going to pop off my heads just to see, though.

- emilio

[neilpaku]

yes, i think the exact mechanism of oil loss and cylinder wall scoring is not well understood. if Audi knows, they aren't telling.

it's my understanding of the Alusil process that leaves me skeptical that a single-step process could do anything significant, especially without new rings (or even oversized ones). note that the OP's Porsche forum link is for a guy that also put new rings in. it may just be the rings that really fixed his compression issues, while the honing was just proper prep for new rings.

from what i've read (Sunnen docs, Porsche forums) making an Alusil block is a three-step process:


bore the cylinder as normal
hone with a compound that just removes aluminum, leaving microscopically sharp silicon (oxide? carbide?) sticking out of the cylinder wall and creating a gap for oil to dwell
hone the silicon crystals so they form nodular profiles, smoothing their surface for piston rings to glide over


any cylinder scoring will be removing both aluminum and silicon from the walls, creating a microscopically out-of-round cylinder. removing those without keeping the rest of the cylinder round may be beyond the ability of existing (or new) rings to fill. the one saving grace is that the final Alusil step is with a silicon grinding compound, which will definitely remove the aluminum as well. so, if your cylinder walls happen to be within a pretty narrow range of scoring depth and piston ring wear then you might be able to improve the conditions without new piston rings by keeping the whole thing round (i.e. pushing the cylinder walls back to the depth of the scoring).

i would be very happy if this worked for someone with well-documented oil consumption, because i might consider doing it, too (1qt/1000mi for me). i'm not going to pop off my heads just to see, though.

- emilio
Sunnen calls that second step the "exposure" step, to expose the silicon nodules. My (wife's) car used a quart per gas tank, smoked on deceleration (valve guides), and a blue haze while under power (leaking past rings). It had no significant oil leaks. The intake runners were caked, both oily and carbonized, the valve guide seals were burnt and hard, I'm not sure of the status of the PCV and EGR system but will check that out, the compression ranged 150 to 180. After removing the heads, there was quite a lot of "wiped" oil residue at the top of each cylinder. The cylinders are very shiny, like the "before" photo in the exposure technique. One of the manual cam adjusters had the internal pin boss smashed out so was dysfunctional, the other one was barely worn. The two usual chain guides were broken and mashed up into plastic mush, and the inside of the engine has that brown tinge of "haven't changed the oil enough".
Things I've done include new valve guides and seals, new valley gasket and check valves/jet (although my existing ones held oil for the past 12 months so I guess they're in good shape : ). I'm about to pull the pistons to inspect and likely clean the rings and piston crown.
I suspect that apart from losing oil via the guides, my rings are either stuck or choked, and/or the oil ring is not sufficiently wiping due to glaze. So the next step is to deglaze and re-expose. I suppose it's possible that I could end up using more oil afterwards but I feel like I was already at the extreme end of the oil consumption bell curve. After examining the rings and gap I'll decide whether the rings are still serviceable. The car has done 120k (40k with me) but I suspect that the engine in it may not be the original - if so, I would have no idea how many miles it has done. It has plenty of hallmarks of being apart before with kludges left and right. However after this effort I'll know exactly how it was reassembled.

[badger.]

little discussion here, bout 2/3 down:
http://www.eng-tips.com/viewthread.cfm?qid=82031

[neilpaku]

Update on the reconditioning process (taken a while but I'm in no hurry). Reassembled the engine including new piston rings after the Sunnen paste hone and new valve guides/seals. Some pictures including one of the lower right chain guide on the main (center) timing chain. The plastic insert split at the lower/left end and was loose. Replaced that along with the usual other two guides (plus for grins did the PTO guide and all chains because I forgot to label which way round they ran before removing them....). Sixth picture is for the guy that couldn't tighten up the cam bolts - have to use a wrench on the other end of the camshaft to hold it. I kept the timing bars in the slots, not to hold it, but to help me keep position while I held the cam wrench in one hand, and the torque wrench and break bar in the other.

http://www.audizine.com/gallery/data/500/IMG_3506.jpg

http://www.audizine.com/gallery/data/500/IMG_3507.jpg

http://www.audizine.com/gallery/data/500/IMG_3508.jpg

http://www.audizine.com/gallery/data/500/IMG_3509.jpg

http://www.audizine.com/gallery/data/500/IMG_3505.jpg

http://www.audizine.com/gallery/data/500/IMG_35121.jpg

http://www.audizine.com/gallery/data/500/IMG_35181.jpg

http://www.audizine.com/gallery/data/500/IMG_3519.jpg

[BCsniper]

No before/after pictures of the cylinders using the sunned paste?

[Cygnets]

No before/after pictures of the cylinders using the sunned paste?

Would like to see that too

[2004B6S4]

Me three. And compression test results before/after would be awesome if you have those. I'm not sure if you mentioned it but did you have any significant scoring or oil consumption before doing the hone? TY for contributing this, I've been looking forward to the results

[neilpaku]

I did post some but couldn't find the danged thread (it's obviously not this one : ) - that thread is in here somewhere. The upshot is that the bores were shiny like chrome before, and then after a light scrubbing with pot cleaners, and then the paste, they came out a dull matte. Didn't make any difference that I could tell to the scoring so #1 and 2 will still chew a bit more oil than the others.
Oil consumption was about a quart per tank of gas, and compression was 135 to 180 (I wrote 150 to 180 originally but that was incorrect). Got about 17-18mpg and ran along in a cloud of constant blue smoke. I'm looking forward to much better results : ) but won't be surprised if the oil consumption is still high. What will make the big difference though is having the camshafts correctly timed. I doubt the right cylinder bank contributed anything to making the car move.

[neilpaku]

I found the old photos so am posting them here. In no particular order:
- fitting new rings to pistons
- broken cam adjuster - this was what the engine was running on
- three-arm hone with felt pads (from Joann home craft store) and Sunnen AN-30 paste. Ran this on my drill's slowest speed - prob. 60-100 rpm
- using painter's tape to cover all holes downwards of the cylinder being worked. Start at the top and peel them off as you work down
- The bottom cut out of a plastic ice cream pail and pushed to the bottom of the bore to stop paste going into the crankshaft cavity. Lots of paper towels to clean up the mess before/after honing
- Bore after honing - matte finish. Before, it was shiny enough to see my reflection.

http://www.audizine.com/gallery/data/500/IMG_3361.jpg

http://www.audizine.com/gallery/data/500/IMG_2355.jpg

http://www.audizine.com/gallery/data/500/IMG_32561.jpg

http://www.audizine.com/gallery/data/500/IMG_32551.jpg

http://www.audizine.com/gallery/data/500/IMG_3260.jpg

http://www.audizine.com/gallery/data/500/IMG_3261.jpg

[q_dubz]

this makes me excited to get started on my spare block :)

[BCsniper]

The fact that this didn't seem to affect the score marks makes it seem less promising

[q_dubz]

The fact that this didn't seem to affect the score marks makes it seem less promising

Those don't even remotely count as score marks. Furthermore a picture doesn't tell us much of anything in this case. Hell the carbon at the top of the cylinder is more pronounced than those lines which aren't even on the piston riding surface of the cylinder (left and right sides, think of rod/piston angle)

People keep blaming it all on cylinder scoring, and while that might attribute to SOME oil consumption, the main cause is in the block alloy itself. Silicon is extremely abrasive and in such it cause the rings to wear in and eventually wear out very quickly furthermore once the cylinders glaze over, the seal is pretty much gone.

[neilpaku]

: ) That's not the scored cylinder; that's one of the good ones. I checked the old rings and they were pretty close on the ring gap so I don't think they were very worn (or the block wasn't very worn) but I'm not experienced with alusil bores so don't have a good feel for what impacts consumption. I definitely agree with you though that in general, a deglaze should help a lot. I'd wager most of the oil was going out #1 and 2 (after the guides - they were REALLY worn. Surprised at how bad this engine was but then I suspect it's not the original). If I really wanted to know, I'd have tested like this:
- clean old rings, refit, and test oil consumption (they were pretty sticky in there)
- then hone cylinders, refit old rings, and test oil consumption
- then fit new rings and test consumption.
That would have a good chance at identifying which items were most responsible for consumption, although it's always hard to control all variables. In my case, if the consumption goes down (to one quart every two gas tanks), I'll be happy - I'll have halved my consumption!. Replacing rings and honing/boring cylinders go together naturally in a teardown so I'm ok with that. It's all just dollars at the end of the day : )

(Update - in the second to last photo you can see how glazed that cylinder was - that was after wiping it down with shop rags)

[ZimbutheMonkey]

: ) I'd wager most of the oil was going out #1 and 2 (after the guides - they were REALLY worn.)

In addition to everything QDub just said, neilpaku identified another issue that I think a lot of people forget when assessing the condition of the block is that bad guides and stem seals can account for a ton of oil consumption, especially during log periods of vacuum like highway driving.

As I understand it, bad rings will cause oil consumption on hard acceleration, but oil loss under vacuum is more of an indication of wear in the valvetrain seals.

In fact, a buddy of mine who has his own shop had an S4 which was consuming a lot of oil, turns out that the heat from the cats had basically melted the valve stem seals. Changed them out and bang, no more oil consumption.

Anyway, just something to think about before condemning a bottom end.

[kevinye77137]

I second zimbuthemonkey's post. A lot gotta do with stem seals and not always scored cylinders. I pulled my intake manifold out recently and found a small puddle of oil on my valves and the bottom of my IM. There should be a stem seal valve DIY if anyone has the knowledge and time to post it on forums. It's really sad how people just trash their motor because of oil consumption and assuming cylinder scoring is the main cause of the consumption when really the stem seals should be the first thing to suspect since it's way cheaper and easier to change. Someone make a valve step seal DIY please!

[neilpaku]

I had the shop do the guides so they did the seals at the same time, but before I dropped the heads in to them, I checked a couple of seals and they were hard, like hard plastic. The stems were covered in oil, and the intake runners were soaked in oil and carbon. I can't imagine that the seals were functional at the end. With the timing being so retarded on the right bank due to the broken adjuster, I'd guess that the compression stroke was blowing the leaking oil back up into the intake manifold.
I'm going to open up the intake manifold this week to check it over and will check to see how oily it is.

[emilio]

i thought leaky valve stems would be evident because they cause smoke on shifting and such. would our numerous cats conceal that? i definitely get sludgy runners and oil in my IM, but i've never heard anyone mention smoke out of my tailpipes.

- emilio

[neilpaku]

Best non-disassembling way I know of to check for leaky guide seals is to throttle off from high rpm, and then throttle on again - you should see an excellent cloud of mosquito-choking blue smoke

[Armagon]

Bringing back and old thread, I see that there was a lot of discusions about re-sleeving or polishing the cylinders walls with AN30

But no one ever talked about reboring a minimum to make scorings disappear and applying a nikasil coating.

That would be the cheapest way to effectively fix the scoring problem, to my opinion.

[VinnysS4]

Bringing back and old thread, I see that there was a lot of discusions about re-sleeving or polishing the cylinders walls with AN30

But no one ever talked about reboring a minimum to make scorings disappear and applying a nikasil coating.

That would be the cheapest way to effectively fix the scoring problem, to my opinion.

I have personally took the special honing stones and honed just a tiny bit amount a way to get rid of the scratches. I then used a 3-stage honing process with the paste and felt pads. I did not have the cylinders coated after the process as they were never coated with that from the factory. Plus getting that done is not exactly cheap.
I replaced the piston rings and valve seals while I was inside the engine. The car in question has not had oil consumption issues since the honing was done. Compression numbers were very close to factory when everything was said and done.

All that being said, I am not an expert nor do I own a machine shop.

Sent from my SM-N920V using Tapatalk

[DevenReilly]

I have personally took the special honing stones and honed just a tiny bit amount a way to get rid of the scratches. I then used a 3-stage honing process with the paste and felt pads. I did not have the cylinders coated after the process as they were never coated with that from the factory. Plus getting that done is not exactly cheap.
I replaced the piston rings and valve seals while I was inside the engine. The car in question has not had oil consumption issues since the honing was done. Compression numbers were very close to factory when everything was said and done.

All that being said, I am not an expert nor do I own a machine shop.

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I'm pulling my motor for the timing chain service. Thinking about doing the whole 9 while its out. How are your results holding up? Mind sharing the process you used?

[VinnysS4]

I'm pulling my motor for the timing chain service. Thinking about doing the whole 9 while its out. How are your results holding up? Mind sharing the process you used?

I did this on a fellow forum members car several years ago. He went from low compression on a few cylinders to excellent compression. I’d have to dig for the numbers, but if I remember correctly, he went from 110ish up to 150-160 and his oil consumption went from a quart every couple hundred miles to not needing to add any oil in between oil changes. Haven’t heard a single complaint over the last 3 years.
I ordered some of the sunnen alusil honing stones in 2 grit types and I also did a felt hone at the end. I used honing oil during the honing process and then switched to the felt pads and the sunnen paste to do the final honing process. The idea isn’t to remove much material, just enough to take the scratches down so they no longer catch on the finger nail. Also to remove any glazing and piston chafing caused by side loading. Over time, aluminum and small bits of carbon get trapped in the pores of the alusil. The felt honing process removes the aluminum and leaves the microscopic pores empty to allow oil to sit in them. The felt honing process is self limiting so you technically can’t over-do it. The felt and paste are less abrasive than the silicone so you won’t change the bore shape/size. You’ll just remove some of the aluminum that sits in with the silicone. This gives the rings a nice smooth layer to ride on.
I had a friend modify a cheaper hone and also modify the stones to use the sunnen honing stones. The hone they sell specifically for their stones (they don’t fit other hones) is kind of pricey if you don’t plan on doing it more than once or twice. That’s why I went this route.
I also re ringed the engine as the old rings were coked with oil and whatnot. I also did a valve job and threw new valve seals into it. I’m sure this helped with compression and oil consumption as well.


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[DevenReilly]

I did this on a fellow forum members car several years ago. He went from low compression on a few cylinders to excellent compression. I’d have to dig for the numbers, but if I remember correctly, he went from 110ish up to 150-160 and his oil consumption went from a quart every couple hundred miles to not needing to add any oil in between oil changes. Haven’t heard a single complaint over the last 3 years.
I ordered some of the sunnen alusil honing stones in 2 grit types and I also did a felt hone at the end. I used honing oil during the honing process and then switched to the felt pads and the sunnen paste to do the final honing process. The idea isn’t to remove much material, just enough to take the scratches down so they no longer catch on the finger nail. Also to remove any glazing and piston chafing caused by side loading. Over time, aluminum and small bits of carbon get trapped in the pores of the alusil. The felt honing process removes the aluminum and leaves the microscopic pores empty to allow oil to sit in them. The felt honing process is self limiting so you technically can’t over-do it. The felt and paste are less abrasive than the silicone so you won’t change the bore shape/size. You’ll just remove some of the aluminum that sits in with the silicone. This gives the rings a nice smooth layer to ride on.
I had a friend modify a cheaper hone and also modify the stones to use the sunnen honing stones. The hone they sell specifically for their stones (they don’t fit other hones) is kind of pricey if you don’t plan on doing it more than once or twice. That’s why I went this route.
I also re ringed the engine as the old rings were coked with oil and whatnot. I also did a valve job and threw new valve seals into it. I’m sure this helped with compression and oil consumption as well.


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Awesome thanks for the info. I've been doing a lot of digging around on the forums here seeing that some people have completely failed to get the piston rings to seat after the cylinder bore resurface. Did you use conventional oil for the break-in? There seems to be a lot of conflicting information on here about whether to use the stones or just do the felt pads + AN-30.

I didn't do a compression test before I started the engine removal process however I did see some light scoring on the walls of cylinder 4 through my bore scope cam, doesn't look like anything too deep but I guess I'll find out once the heads are off. The car has been blowing blue smoke out the back on startup so the valve seals are definitely getting replaced while I'm in there.

[neilpaku]

Coming back to this thread after seven years and 130k miles. Recapping, in 2016 engine failed with broken camshaft adjusters and guides. At that time I also did the felt hone and new rings. Oil consumption dropped from a quart every tank or two down to a quart maybe every 3k and it stayed there. Now in 2023, "something" happened to the passenger side timing chain assembly leaving the lower metal guide broken and evidence of valve to piston contact which could have only happened if the intake valves started opening earlier which I can't find an explanation for. I'll be putting new diamond washers on just in case but those cam bolts were torqued on there solidly from last time.
Anyway, cylinder #2 has a finger-nail catching scratch so I'm contemplating the Sunnen honing stones to knock it down a bit followed by the felt hone, and a new set of pistons and rings - the current pistons have 220k on them and a fairly hard life so time for a changeout. Heads have been revalved and guided same as last time. Engine wasn't using much oil after 130k. Bores aren't that shiny but I'll give it a hone anyway.

[q_dubz]

hmm interesting doesn't make sense...maybe rocker arm tappets?