Do these pistons look ok? (Detonation)

[Hmh800]

Hi guys-
I’m starting to put my motor back together after timing belt slipped. Had heads rebuilt and replaced 6 valves. I’m just cleaning up the tops of the pistons and noticed these pits in cylinders 3,5, and 6. Others look fine (aside from marks from valve collision). I hadn’t noticed them before, and wasn’t going to tear the bottom end of the motor apart. It’s really clean internally.
What are your thoughts? Is this a red flag to assemble motor as is? Car had an apr tube and has about 160k mi. Cylinder bores all look good with crosshatch still showing. I am going stage 3 with k04 turbos…
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[LJS]

FWIW-
If this was my motor I would do the following--
1. Remove all the pistons and insure all the rings move EASILY(rotation) to insure there's no land damage(collapse...)
2. Inspect the rod bearings for abnormal wear
If ok I would smooth down all sharp edged on the piston crowns(from the valve contact) button her up and run it
PS- if the rod bearing look suspect then go after the mains-inspect the bearings and crank

[Silverex]

^+2

My pistons looked very similar and all the rings were beyond caked up to point they wouldn’t spin

[Hmh800]

So I pulled the #5 piston which showed the most pitting on top and here’s what the bearings and rings look like. Whadya think? Rings are not stuck and spin freely. Crank journal is spotless. The only area I question is top half of bearing.

[LJS]

The piston looks good
Pull the other 5 and compare---
My opinion---I would consider a mild rebuild--replace those bearings at the very least.

[RMode]

Bearings look fine for 160k. Since you’ll have it apart, fresh ones, at whatever clearance those are, and you should be good! And get a good torque wrench, do your assembly in a clean room with some sort of exhaust fan if you can, and not humid. At K04s you don’t need rods, but while you’re there…


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[Hmh800]

Remode, it’s a slippery slope! Trying to stem the bleeding but not cut corners.

[Hmh800]

Anyone know what the rod bearing clearance spec is?

[RMode]

I think I can speak for everyone when I tell you “I understand”. Even the proper ones done on a budget have big numbers associated with them


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[CELison]

Anyone know what the rod bearing clearance spec is?

https://www.audizine.com/forum/showt...links-document

[Hmh800]

Thanks cel, I can’t seem to download it on my iPad but I’ll try at home with a real computer.

[Silverex]

Honestly since everything looks good enough I’d just slap it back together as is (reusing rings/bearings) or go down that slippery slope.

When I was in your shoes I did a full rebuild with rods and I’m really happy I went that route 35k/3yrs later. All said and done it wasn’t that expensive…I had a machine shop deck heads/valve job, and balance rotating assembly. Everything else I did myself, probably had about 800$ at machine shop, $450 on rods, and about $500 for new rings, bearings, bolts etc. So let’s say 2k all said and done.

I also replace all the seals/Orings/gaskets/timing parts but didn’t add that in since you’ll probably be doing that either way.

If you end up rebuilding lmk and I’ll give you all the specs I used.

[Tightmopedman9]

Out of curiosity, what tune was on the car that caused that much detonation? ME7 does a good job of applying pre-emptive/adaptive ignition retard, fuel enrichment and boost reduction to reduce knock. My guess is that there were some safety features disabled in the tune...

[Hmh800]

It was an APR tune that was installed before I got the car. I can't say that it was the tune that caused the detonation.

One issue that I was never able to resolve before the engine was damaged from the timing belt was that at WOT in third gear or higher (think getting on the freeway) the car would stutter hard like the ignition was cutting out. I think it was ignition vs fueling or something else because it was so sharp. I don't know if this was related to or causing the pitting on the piston tops; I am replacing the coils and ICM's as part of the rebuild. I hope this resolves the issue. It never threw a code for ignition. Anyone have any ideas on this?

The other part that seems odd to me is that there was a fair amount of carbon deposits on the tops of the pistons, which to me would indicate running rich. I've thought that detonation was more prevalent in a lean condition. Is my thinking correct on this?

Anyways, I'm now waiting on new rod bearings (big ends) and bolts then I'm ready for assembly! I've got everything cleaned and ready. I'm looking forward to the clean part of the build and obviously the end result!

Thanks to all you guys for the help. This forum is great!