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?

Originally posted by rhui
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.

shit mine always sounds like that under load... only its 100 spray can rattles... oh wait your talking from the engine, mine comes from the exhaust... :shrug

lol sorry... how long have you been running those pistons?

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

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




best time so far 14.3 @ 101.1mph(no traction)
www.cnnmotorsports.com

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 bullettdsm
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

exactly right ........I had that happen to 2 sets of pistons on a v-8 not running a air cleaner for long periods of time.Strange things can happen though during a rebuild.Maybe some debris in the intake-mani, did you have any work done to it or the head that might of left some shavings in there? What about your intake pipe? did you have to cut it? was there and shavings or an edge left from cutting that could of broken off? Was there use of a ring compressor when they were installed lol?

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

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.

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

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

hmm i have a piston that that happened to also.. unfortunately the electrode decided to stick in the cylinder wall and cause some major problems.. wish i woulda taken pics of the walls.

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

My thoughts exactly. I had a center electrode insulator come apart and the damage looked similar, although mine was much worse. You will likely have corresponding marks on the cylinder head. It's definately not detonation.

Originally posted by bullettdsm
Pre-detonation will give a smooth burn effect (usually white like exteme97nt's).

um.. pre-detonation? theres detonation, and pre-ignition.

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.

Originally posted by grain

Originally posted by bullettdsm Pre-detonation will give a smooth burn effect (usually white like exteme97nt's).

um.. pre-detonation? theres detonation, and pre-ignition.

Yeah, I just put the two together to make a new word lol. Sorry typing too fast. Got ideas mixed up. My sinceeereesttt apologies:bowdown

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?

Originally posted by rs-pssst
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?

Only if the debris got caught between the valve seat and the valve. Depending on the size of the debris (which I doubt it was that big) You have an outside chance of bending a valve (really unlikely). Regardless, you should pull the valves and check. If it is just surface marks on the outside of the valve face, you can just smooth those off. Keep in mind if you did not find any debris it could very well have gone out your exhaust valve and been blown out. The bigger question is where did it come from? Rings? Spark plug? Or just some foreign matter that somehow got caught in the intake and was sucked in to the chamber. With the compression that you are showing, I would be suspicious of it being a piece of ring. It's possible to break off a piece on install and you may not have noticed. Of course that means pulling the piston.
Good luck,
MB

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.

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.

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?

Originally posted by rs-pssst
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?

992gnt makes a good point. Debris could have damaged turbo.

There are a lot of different ways to pop the springs on your valves. The way I do it is make a lever jig of some sort that allows you to compress spring while holding valve in place. The gist of removing the valves is compressing the spring so that you can freely remove the keepers. Then you can just pull out the valve. Unless you have the jig, I don't know if I would recommend you doing it. If you think you can compress the springs while holding the valve closed, then that is your call. Who did the engine work for you? Did you work with a machine shop at all? If so they should be able to quickly pull the valves for you (I would think at no cost).

But the bigger question is what about the compression? you need to find out why the bad compression. Is there something stuck on the valve seat? Are you sure that there is not a small piece out of the end of the rings? How damaged is the cylinder? You need to find out why and fix.

Now, I have seen brand new rebuilt engines that have low compression in one cylinder when there was nothing "wrong" (tolerances in rings and ring galleys, cheaper piston sets etc. You run it for a while and numbers came back up) but that is a pretty drastic % change from cylinder to cylinder (almost 50%).

Good luck
MB

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

Originally posted by rs-pssst
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.

HAHA um I'm an idiot... I missed this earlier, and I think just about everyone else did too.

You had a spark plug electrode go through your piston. Problem solved.

Edit- FWIW, detonation probably broke the spark plug off, or you were using a crappy brand of plugs.

Originally posted by bullettdsm
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

I agree with you: I've pulled many a motor down and that is not detonation..at least not the kind I'm familiar with... :).
It looks to me like trash is coming thru and hitting the piston....unless he used a punch to install the pistons!!
I suspect trash (no air cleaner?)in the intake manifold and/or head coming thru...boosted! But then, I'm just an old Top Fueler fart...whadda I know??

Originally posted by rs-pssst
20lbs cannot be run at 93 octane without timing adjustments and keeping an eye on the egt's.

Sorry, but thats not right. Ive run up to 23lbs of boost on my car without a problem on pump gas and without timing adjustment.

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.

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?

Originally posted by thedawg
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?

It very easily could have been caused by detonations.


Right threy is a piston out of my drag car that detonated at 25 psi of boost at the Mopar Nationals.

You can see the same pock marks on the reverse side of the piston. The pock marks on the near side when to the next level when it melted through.

The deep scratchs are the cause of the bits of aluminum from the top, that missing aluminum from the pock marks had to go somewhere, and it left those grooves. It also doesn't help that the extreme heat from the detonation causes the piston to grow taking up the clearance. This engine was blue printed and the clearances where correct, the extreme heat made the piston grow to much and the bits of aluminum from the top couldn't fit through the gap.

No foriegn object went through this piston, the clearences where correct. This is pure detonation damage, and what would have happened had he continued to run it.

The damage on this piston was purely my fault, and a result of tuning when we were playing. It is pure detonation damage in the extreme.

Gary

PS I reused the rod and bearing, as they were fine.

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

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.