These are low compression JE pistons connected to eagle rods. Can anyone tell me what this damage is from?

There is cavitation located on the top of the piston shown in the picture below. My guess is detonation.... has anyone seen this before and what most likely went wrong?

I believe that is caused by some form of high heat...
You'd know if it was detonation if you heard some type of spray can rattling noise during load.

I wouldn't worry about that as much as I would worry about the blackdeath you are getting on the side of the piston...

Means the piston was getting very hot, and scuffing the sides of the cylinders.

Ignore me if Im wrong, I'm only guessing cause it looks and seems similar to what happend to my stock piston after running a badly tuned fuel map.

do you have a EGT gauge? if so, whats your readings like?

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It could be detonation. What did the spark plugs look like?

Joe
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It looks more like debri than detionation. This is what detionation looks like (My old Pistons)




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That was from running 23lbs of boost with the hahn portfueler and with a 30% mixture of xylene. The xylene ran out and i continued to boost around 20lbs. I didn't have an EGT gauge (gettng one now), but the AFR were around low 10's. Also no timing adjustments were made... let this be a lesson.. but i pretty much already knew that already... 20lbs cannot be run at 93 octane without timing adjustments and keeping an eye on the egt's. Maybe an egt gauge would be helpful in a portfueler setup seeing that it runs 1100

I'm not a turbo guy but I have built and broken down many engines. I have seen detonation of many kinds (even to the point of burning thru the piston). I have also seen multiple cases of some piece of debris inside the chamber. Either you hit the piston with a pointed steel hammer to get it out or you had debris in the chamber some how. I know of no event that I have seen or heard about that will cause the sharp dents in your pistons. Remember, they call it burnt piston for a reason. Pre-detonation will give a smooth burn effect (usually white like exteme97nt's). Sharp raised edge pits can only be from a piece going into the metal and causing a crater. How does the rest of your chamber look? Do you have scratches on the sides of your cylinder? May not depending on the material but it did look like one of those rode the cylinder.
Good luck,
MB

Originally posted by extreme97nt
It looks more like debri than detionation. best time so far 14.3 @ 101.1mph(no traction) www.cnnmotorsports.com

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You could also look at the head, if you see similar marks then more than likely it's some kind of debris.

afr was low 10's
isnt that very rich
i thought detonation came from going too lean

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detenation can also be found from too rich mixtures also.. and 20psi is quit a bit too much on stock timing. We start to knock at around 15-16psi on the stock timing map. If i was you i would pull your boost down to about 15psi until you get a good way to control your ignition timing.

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Looks more like you lost a sparkplug electrode and it assed off on that piston. That's not detonation.

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Greg

'19 Genesis G70 3.3t AWD
'88 Chrysler Conquest TSI

Its not from any form of detonation at all.

It's a foreign object/debris that not only smashed up the tops of the pistons, but got lodged between the piston and the cylinder, which probably destroyed your block (or gouged it nicely) too.

It's most likely spark plug electrode, chunk of ring, wrist pin retainer, or something that broke off the head, possibly a valve chunk.

The only role detonation or EGT plays in all this is possibly CAUSING whatever broke off to break. The damage is a direct result of metal chunks bouncing around in the engine.

Thanks guys for the info.... I will have to look at the bottom of the head to see if i can see anything..... I had low compression in that cylinder #1 with it being 80lbs and the rest being close to 150. can't see any visible damage on the cylinder walls. i will inspect them more closely and report back. When you had depris, did you have to change the valves?

How did the rings look when you pulled the engine apart? If it had low compression in the cylindar and you had debris in the chamber, I'd be willing to bet that the top ring was shattered. But thats experience with N/A engines (name any) not neccesarily a turbo'd 420a.

EDIT: Back in high school my buddies Datsun went ass-crazy so we pulled the head and found to very tiny metal balls that turned out to be leftover springs from a botched carburator rebuild.

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Also look at the wheel on the turbo. If the motor did ingest something, and it's not mashed into the bottom of the cylinder head, you may very well have some damage to the hot side of the turbo as the chunk of stuff passed through.

Greg

'19 Genesis G70 3.3t AWD
'88 Chrysler Conquest TSI

Looking at the rings, there is no visible damage to the top one or the bottom one. I am sending my pistons out to the machine shop today for closer inspection...

I already threw out my old plugs because i changed them thinking that the bad idle was plug related, i did not inspect them too closely, but when it was idling, we yanked off the spark plug wire to that cylinder and the sound of the bad idle didn't change as opposed to when we yanked off the other cylinder wires and the idle sound changed dramatically.... so maybe it was debris from a spark plug.

I have to check on the valves from under the head on the weekend and possibly yank out the valves, should i have a machine shop take the valves out, or is this inside the scope for someone that has never changed valves before, but has a copy of the service manual and 2gnt?

hey how much do new keepers, cost, i doubt i'm the only person here to lose one, i guess they only come in like a pack of 32 or somethin

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They have been run lean and had serious detonation. They were close to seizing judging by the skirts. If you measure the piston diameter 1 inch above the bottom of the skirt I think you will find it undersize from being rocked severly in the cylinder.

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Um Gary, I don't disagree that those pistons saw some detonation.... But that's not what caused so much damage that they had to be pulled.

Picture #4 of 5 (middle pic) shows three distinct types of damage

1) Thrust face (perpendicular to wristpin) wear. Caused by either incorrect clearancing, or detonation.

2) Deep skirt scratches near wristpin. Caused by either bad rod bearings, bad wristpin, bad piston, or foreign object.

3) Piston face pitting. Caused by foreign object.

Detonation is simply not strong and localized enough to cause damage #2 or #3. Damage #1 is present on ALL used JE pistons to some extent.

Extreme97NT posted some other pictures of 4 pistons that were detonated to death. Maybe that's what you were referring to?

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Hehe your picture is a perfect example of what I'm saying.

The skirt and top of your piston shattered, thats the foreign object that caused the pitting in your case. You had chunks of piston and rings smacking around in there.

Same with the skirt damage in your pic, it wasn't caused by the detonation rattling the piston around so much that it scraped against the walls. Yours clearly blew up, chunks bounced around in the cylinder, and then ate their way down the cylinder.

In the original posters pics, you see no piston chunks missing, so the foreign object was something else, but whatever it was, it ground its way through the side (not the thrust face) of the piston.

Detonation melts things up to a point, then the metal fails and simply breaks apart. The original poster's pistons did not melt or fail, something else did, probably due to detonation, and whatever it was that broke apart took the pistons with it through mechanical damage. Pits in piston tops come from broken pieces of metal, not the detonation itself. Detonation just helps the pieces GET there.

Detonation makes BIG holes, not little bitty ones. The little bitty ones are from shrapnel.

Figured I'd post this since we're on the subject.

http://www.streetrodstuff.com/Articles/Engine/Detonation/


Brian

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I picked a picture of detonation at the extreme. None of the damage was caused by the ring, as all the ring was still present. I broke the last peice off before the photo.

I need to find other pictures from other pistons over the years. Detonation does not take big chuncks. I have seen detonation look like you sand blasted on part of the piston causing a divot.

I know exactly what caused the damage on my piston, I was all detonation. One of the most important things you need to learn is failure analysis when looking at an engine failure. You need to look past the effects, and look to the cause.

I have had guys tell me a rod broke. I can't honestly remember seeing an engine with a broken rod that the rod was the cause. Every one I saw it was the effect, the cause was usually a bearing failure or oil starvation.

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