What caused this?

[Mike T]

A very small piece of debris could have caused this and something could have easily passed by the throttle blade without damaging it. The thing I have a problem with is that it doesn't seem likely that one piece jumped back and forth between the cylinders. I see what you are saying about the appearance of cylinder 4. Is it pitted in addition to the somewhat scratched look? Are the cylinder walls scored at all ?

 

[87gnturbosix]

Here is a pic of the turbine wheel. I was thinking debris when I first saw it but the TB blade looks good and I don't see any nicks on the turbine wheel. Does the wheel look normal? This turbo has close to 25K miles on it.

 

[87gnturbosix]

A very small piece of debris could have caused this and something could have easily passed by the throttle blade without damaging it. The thing I have a problem with is that it doesn't seem likely that one piece jumped back and forth between the cylinders. I see what you are saying about the appearance of cylinder 4. Is it pitted in addition to the somewhat scratched look? Are the cylinder walls scored at all ?

Cylinder walls look good. I like a good mystery but not when it comes to my motor.

 

[Pittsburghkid]

Have you checked the heads and deck with a straight edge?

 

[haywire4130]

definately looks like damage from foreign body but very unlikely/almost impossible it was one piece that went from cylinder to cylinder. what was the reason for the rebuild/piston replacement in the first place? if it was a blown head gasket, what type of head gaskets were you running before? only reason i ask is cometic or other steel shim gaskets can leave small steel shards behind when they blow apart. also, what do the spark plugs look like, and how long did the motor sit between the time you assembled it and the time you ran it? got any enemies with access to your shop?

 

[Mike T]

This first pic is of #2 piston here is #4 and #6. 6 looks like 2 and 4 looks more like scratches.View attachment 194458View attachment 194459

Cylinder 4 at the 7 o'clock position appears to be eroded. Is that just how it appears in the photos or is it damaged ? Could you get a close up photo of that area on #4 and maybe another close shot of one of the others?

 

[BEATAV8]

Regarding the turbine wheel, you need to look at the leading edge of the blades, in that picture you can only see the tailing edges. Need to look inside and see if there are chips taken out where the exhaust first comes into contact with the turbine wheel. In the volute area. Check each and every blade.

 

[87gnturbosix]

Thanks for all the replys and help!!
I looked at each leading edge and found 1 nick. The rest were intact and one other had what looks like the start of a tear. I don't have much turbo experience but the rest look like normal wear and tear after 25k. The way the pistons look shouldn't there be obvious carnage?
The #4 piston doesn't appear to be damaged at 7oclock. I tried to take a better pic but it didn't turn out any better.
I remember how the scratchs got on #4. I broke the cam in with light springs and putting on the new I dropped a valve in that cylinder. Using a coat hange I was able to get it back into the guide without removing the head.
Reason for rebuild was spun bearing. I went back with stock type gaskets, I think they're calledcomposite. Spark plugs look normal. Motor prolly sat a month or so before I ran it. As far as enemies, sometimes my wife hates the car.

 

[haywire4130]

Hahaha vengeful wife would be a bad scenario! Are you running a cat in this car? If so you could pull it and look in there for evidence.

 

[87gnturbosix]

Hahaha vengeful wife would be a bad scenario! Are you running a cat in this car? If so you could pull it and look in there for evidence.

No cat.

 

[turbofabricator]

Did the machine shop bead blast the cylinder heads? If so, there is your smoking gun. I've seen guys pick up heads ready to bolt on and have glass bead POUR out of a water jacket. Not un common to find shops blasting heads these days.

 

[Pronto]

I bead blast small castings for my work. It's not usual to have residue beads hiding in the castings. I can easily see some getting left behind when blasting heads.

 

[Chuck Leeper]

You glass bead the intake??

What Ken said.....
Guess I was too specific w/ the ?. Cyl heads that were mentioned, WILL do this.
Was involved in a lawsuit w/ this very thing.
The powder coating shop uses bead blast to clean parts. They did an entire BMW engine...it ran about 10 mins.
Suit dismissed...Judge determined the BMW shop was responsible for the cleaning. [We found nearly 3 oz of blast matl in the oil pan.]

My $.02.........That's not detonation.

 

[Pronto]

For us the only way to make sure all the glass beads or aluminum oxide is off the metal is to ultrasonicly clean it. There is always residue left behind in the beaker.

 

[texasturbo]

what do the rings look like. pull the piston and see if the rings began to separate.

 

[dr_frankenstein]

I never never use glass beads for any engine parts...

glass, crushed slag, oxides, sand and just about any other MINERAL based media is way too hard and doesnt break down is a major no no for engine parts.

thats why they make walnut shell, 3M Star Blast or use Advanced Medias plastic engine media. all recomended for internal engine parts.

 

[Pronto]

I had a block that had a bump in the valley. I poked at it and it flaked off. It had some casting sand inside it. Something like that might have happened?

 

[Chuck Leeper]

"I never never use glass beads for any engine parts..."

Absolutely! We "repaired" a set of alum heads that had been glass bead blasted. [Including the titanium valves.]
The glass imbedded in the stems, ate the guides up, locked themselves in the guides, folded the p rods, & a few had the heads pop off.
The customer demanded to know WTF had happened. We sent the valves to the mfgr. They send us a hi mag pic back. The stems looked like a steel shaft that had been charged magnetically, and stuck in the Magnuflux powder!!