Bearing Clearances

[fast377]

So, I'm building a forged 1.8 for my car and I'm having some trouble with my bearing clearances. Based on the specs in the bentley, I'm out of spec. However, I've seen guys post some rather large clearances used when doing forged engines. So, what's considered out of spec? Old rule of thumb is 0.001 per inch of journal diameter, but that doesn't jive with what's in the bentley.

And why does the bentley say to not do the extra 90 degree turn on the main bolts when checking clearance? If you don't do that extra turn, you don't get the full clamping force, resulting in an incorrect reading (0.0015" difference in my case).

I'm just kind of curious what others are doing.

[PreciseD]

You don't do the 1/4 turn as that will stretch the new (must be new) bolts. The 1/4 turn will not compress the bearing area further. It's to set the torque to yield or stretch of the bolt.

[fast377]

That makes sense. I'm using my old bolts to check the clearance because I didn't want to ruin the new ones. So I since I did the extra 90, will the bearings be bad? I'll back them off and recheck them.

[KHARDa4]

That makes sense. I'm using my old bolts to check the clearance because I didn't want to ruin the new ones. So I since I did the extra 90, will the bearings be bad? I'll back them off and recheck them.

No the spec is 45 ft lbs and a quarter turn. Going the extra quarter turn will not make the clearance tighter. It would in fact stretch the new bolts and backing them off at that point would require new main bolts.

Use your new main bolts and do 45 ft lbs in the right tightening sequence then back them off and check your clearance.

[PreciseD]

That makes sense. I'm using my old bolts to check the clearance because I didn't want to ruin the new ones. So I since I did the extra 90, will the bearings be bad? I'll back them off and recheck them.

Check them without the 1/4 turn. You may just need oversize bearings. It's not uncommon.

[fast377]

Using old pre stretched bolts it will absolutely make the clearance tighter. I measured both ways. 0.0015" difference.

Why would you torque then back off to check? You want to torque it down to spec and measure at that spec. I was just unclear on the extra 90.

Having used old bolts and done the extra 90, has that damaged the bearings? It's the equivalent of over torquing, which can lead to the sides cupping in.


And what's an acceptable clearance? Oem audi or larger?

[diagnosticator]

Crankshaft and rod bearings should be sized for stock factory clearances. The bearings have not been damaged using used bolts tightened to the +90 degrees specification.

[fast377]

Crankshaft and rod bearings should be sized for stock factory clearances. The bearings have not been damaged using used bolts tightened to the +90 degrees specification.

Good to know the bearings are okay. I may have to get the crank turned and get some oversized bearings...I'm slightly larger than factory spec.

[Seerlah]

You are doing it right with using your old bolts, torqued to spec. Once clearances check, then torque your new bolts to spec. I personally use arp assembly lube (not to be mistaken for engine assembly lube).

What bearings are you running? Have a part number too? Quite possibly incorrect spec bearings. I notice there is a lot of wrong parts listed for cars on the internet. You might have fell victim. Or...you picked up cheap bearings. I am a Glyco fan. Same company as Goetze, along with a few other brands.

[diagnosticator]

Good to know the bearings are okay. I may have to get the crank turned and get some oversized bearings...I'm slightly larger than factory spec.

If the clearances are over the max reuse specification, then getting a set of 1st under size bearings and having the crankshaft ground to fit is one option, or you if you can find a crank in excellent condition that is standard size, you could use that instead of the original crank.

[fast377]

You are doing it right with using your old bolts, torqued to spec. Once clearances check, then torque your new bolts to spec. I personally use arp assembly lube (not to be mistaken for engine assembly lube).

What bearings are you running? Have a part number too? Quite possibly incorrect spec bearings. I notice there is a lot of wrong parts listed for cars on the internet. You might have fell victim. Or...you picked up cheap bearings. I am a Glyco fan. Same company as Goetze, along with a few other brands.

They are Kolbenschmidt bearings. That's the oem bearing that IE sells. I'll have to dig the boxes out of my trash box in the garage to get the part numbers.

If the clearances are over the max reuse specification, then getting a set of 1st under size bearings and having the crankshaft ground to fit is one option, or you if you can find a crank in excellent condition that is standard size, you could use that instead of the original crank.

I've been thinking about doing this too. I see them on ebay for cheap, but it would be nice to find one local. That way I could bring my micrometers and measure the journals before I buy.

[Kevin C]

What are you getting for clearance and how are you measuring? My experience is that bearing crush does effect clearance, the shell and the housing elastically deform. However, the amount of change you're getting seems high. Getting housing flanges fully seated is important, oversize OD bearings would make that tough. Any chance that you have shells that are sized for a larger housing and are getting too much crush?

I think Bentley says not to tighten to the final setting so you don't use up your new bolts, the most accurate measurements would be made using final torque values with new fasteners that you then throw away. Also, TTY fasteners typically increase in clamping force from the setting torque as you rotate them to final position. If you look at the stress strain curves for effective load, its increasing up top to the point of necking with a tiny dip. My understanding is that the setting torque is typically at about at about 80% of the linear section. If you're past the yield point but before the necking point, then increasing the torque angles, increases the clamping force. Non standard thread lube changes the torque to clamping force and probably requires a different tightening instructio to get to the desired preload.

Fun fact, Young's Modulus is typically independent of the materials heat treat and the same for un heat treated vs hardened steel. When you put in higher grade bolts, what does changes in the location of the yield point the slope of the rise and the run section is the same (within 10%).



Where I got the photo:

http://sustainabilityworkshop.autode...sics-mechanics

[Kevin C]

Also, an oversized bearing housing will increase clearance.

https://books.google.com/books?id=Ny...torque&f=false

[diagnosticator]

Another advantage of getting a second crank to use, you will be able to select a forged steel crankshaft instead of cast iron.

[PreciseD]

One advantage of getting a second crank to use, you will be able to make sure the crank selected is forged steel instead of cast iron.

That is what I did.

[Kevin C]

Another advantage of getting a second crank to use, you will be able to select a forged steel crankshaft instead of cast iron.

Not a bad upgrade.... Although, I would mike the existing crank first, just to make sure another crank is going to solve the problem.

[fast377]

Not a bad upgrade.... Although, I would mike the existing crank first, just to make sure another crank is going to solve the problem.

I measured it. It's in spec, but barely. It's on the low end of accetable. I've already had this crank polished and balanced, so if I can make it work, I would like to. I'm only running a little efr 6258, so i can get by without a forged crank.

I'll double check the bearing prt numbers to see if they are correct. I imagine they are, as I got them from IE.

[Kevin C]

My understanding is, the factory uses select fit upper bearings to optimize the clearance. That might be enough to get your engine in spec.

[Seerlah]

As long as it's in spec you will be fine. Barely is still in spec and will only make a real difference in oil pressure...which too would be so small to even matter.

[fast377]

It's frustrating there aren't many bearing options for these engines. I built a 403 stroker for a z06 back in the summer, and I had tons of options for bearings. I was able to get the exact clearance I wanted.

[Kevin C]

It's frustrating there aren't many bearing options for these engines. I built a 403 stroker for a z06 back in the summer, and I had tons of options for bearings. I was able to get the exact clearance I wanted.

Looking at ECS tuning's choices for mains, I see three choices for select fit bearings. Unfortunately, I can't find a chart that says what size each bearing is. Basicly, the factory select fitted the upper mains to optimize the clearance, but dumbed it down to just replacing the color bearing you had with the same one that came out. I would consider buying one of each color to see if it helps. They show Blue, Red and Black. I think black is standard blue red and yellow will reduce clearance. I would love to find a chart with some numbers.

It sounds you're not just trying to meet spec, but within nominal. Personal preference is to hit around .0014", I totally understand what you're shooting for a good build, not i got kind of close, should be OK. On the engine I built for my truck , I had the opposite problem, ( another turbo motor), I ended up sending the crank back for polishing to take it down to bit the clearances where I wanted them. I had the crank cut and polished and sent it out for Ion Nitriding. It was a learning experience and the first crank I ever sent out for heat treating. It turns out the the nitriding process grows the OD of the crank a few tenths (per side), that got my bearings clearances out of spec. The deeper the hardening goes, the more it adds. I ended up gaining about .0008". An extra polishing got me back to where I needed to be. The block had been line honed and the bores were to the tight side of spec. When the tolerance stackups all go one way, you can have problems.

BTW, the crank looked amazing when it was done, I had never seen as shiny bearing journals, with a super hard surface that was a lot tougher and scratch resistant. The machine shop I used was impressed and started sending their cranks to out to the same nitrider. The results was very different than the cranks that were salt bath nitrided. that and the risk of warping is a lot lower. I'm not sure if the VW part is hardened from the factory or not. On my Mitsubishi, it was an option but the factory hardened cranks were no longer available, so I ended up making my own. On that engine, I intentionally set the mains to the low side of spec. It was also on a motor that's know to have oiling problems with the rods so I was being extra careful on my bearing setup. Ten years of hard running and no issues.

I picked up that crank used and had it cut undersized so I could get the journals where to match up with availible bearings.

One thing that I have always struggled with is getting good measurements. Personal experience is that my Mitutoyo dial bore gauge has a bit too much spring pressure for measuring bearing inserts. The contact balls indent the bearing slightly and causes the gauge to indicate that you have more clearance than you actually do. I have had better, more consistent results using snap gauges and a set of mikes. The upside with that method, is its a comparative measurement and not affected by the temperature of your shop or the calibration of your micrometers. Despite have a nice set of bore gauges and micrometers, I still double check with Plastigauge. The bore gauges are great on the cylinders and the bearing housings ( no inserts, good to verify if the big ends of your rods are still round).

Funny thing, if you look at ARPs instructions for using their stud kit with the 1.8t motor, the mention that the increased clamping force of their stud kit will distort the bearing housing, and that it should be verified and probably line honed when converting to studs. That seems to say that you want to have the actual clamping force the motor is going to run with when making your measurements.

http://arpinstructions.com/instructions/204-5402.pdf

http://arp-bolts.com/kits/ARPkit-det...?RecordID=1190

EDIT: See Matt's post below, the stud kit needed is a different part number. :)

[Matt Devo]

Funny thing, if you look at ARPs instructions for using their stud kit with the 1.8t motor, the mention that the increased clamping force of their stud kit will distort the bearing housing, and that it should be verified and probably line honed when converting to studs. That seems to say that you want to have the actual clamping force the motor is going to run with when making your measurements.

http://arpinstructions.com/instructions/204-5402.pdf

http://arp-bolts.com/kits/ARPkit-det...?RecordID=1190

FYI, the 'VW water-cooled' kit #204-5402 is not the correct main stud kit for the 1.8T - the studs are about 10mm too short (ask me how I know). The correct kit is 201-5401 (Nissan L20) per ARP, and what I'm running. My machine shop was adamant about align honing the main journals when using studs (vs factory bolts).