Detonation Damage???

[ZZ71s]

Not sure whats causing this. No debris in the chamber. We suspect it could be detonation damage. All the marks in the picture look almost the same up close. Possibly timing issues. This is happening in the 7 the heaviest(7 shown in picture), then in the 6 not as badly, then in the 4 and even less damage. Any ideas or suggestions??

Should we change piston?

[grumpyvette]

Id suggest changing the piston but that looks more like damage from a foreign object,like a bit of valve spring or keeper or a small screw, bits of porcelain, etc. notice how the lowest edge (6-o,clock appears to be damaged where and trapped debris would settle until it exited the exhaust port, between,bouncing around in the engine, that can easily travel up and out of one intake and into another during the overlap period ,that was being compressed between the quench are and the piston
detonation damage tends to be concentrated more on the piston edge, valve notches or other places that are not as easily cooled as the flat surface of the piston, and usually looks like the aluminum's been partly melted or frosted


http://www.streetrodstuff.com/Articles/ ... Page_3.php

http://www.kitcarmag.com/techarticles/e ... index.html

http://www.marinesurveyor.com/boatpoker ... piston.pdf

http://www.madsens1.com/saw%20piston%20fail.htm

[ZZ71s]

We thought that also might be the case. Possibly part of a spark plug. The marks are all pretty much uniform so that makes more sense. But we have yet to find the debris. Thanks.

[grumpyvette]

it could easily have been flush out the exhaust at some point

if the edges of the piston lands look rounded off slightly and FROSTED that's the results of detonation, the rough stuff it micro sized bits of molten piston aluminum , that got transferred to the combustion chamber and exhaust port surfaces


btw heres typical detonation damage, and in this case, resulting from a bit of nitrous, that boosted the pressure, but the results would be similar on a high compression engine subjected to crappy fuel and high loads at high rpms without nitrous, notice the sugary/frosted appearance and rounded edges of the melted areas




damage to the ring lands can be caused by detonation or just the ring gaps set to tightly

[TImAT]

I agree with Grumpy on the possible spource of the damage. The thing that would concern me is the damage right at the 6 o'clock position on the piston. Looks like it may be into the edge- if that's the case, make sure there aren't any sharp edges- good place for a crack to start.

[Indycars]

Welcome to the forum!!

Hope you will check in often now that you have posted....you are just like one of the family now!!!

[grumpyvette]

"OK Grumpy ,what caused this"




Its very difficult to come up with a 100% sure diagnosis without on site detailed examination of all the parts, obviously it helps to measure and know the circumstances that were involved,I wish I could examine all the components like heads, head gasket, and the block, bearings etc.
but just looking at the pictures, it might be detonation related but looking carefully , Id say the ring gap was minimal or there was a good deal of crud behind the rings and that might have restricted movement and cooling, a leaking head gasket letting coolant into the combustion chamber and the in ability to compress liquids being at least a factor, it looks like the ring ends touched locking the piston in the bore for an instant resulting in a busted ring land in the piston, OR you got into a hydraulic lock, condition as coolant got in past the head gasket , heat or detonation damaged.

RELATED INFO

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[grumpyvette]

detonation in an engine is only occasionally audible , to the cars operator, many people wrongly assume if they can,t hear a ping or knock theres no detonation occurring.
yet detonation will still raise temperature in the combustion chamber ,to the point that it starts a cascade effect,and can still significantly raise the combustion temperatures and weaken the rigidity of the aluminum alloy used in a piston. as little a a few seconds running time under high loads and high rpms can result in detonation damage to a piston and rings.
http://www.angelfire.com/pa3/lyzcoinc/detonation.html
Detonation is the unwanted burning of fuel in the combustion chamber during firing. The fuel is ignited by something other than the spark plug. This is very bad for an engine. It will usually damage the head gasket and blow it out. However it does put more stress on the cylinder head also.
Causes of detonation:
1. Low Octane Gas.
2. Timing incorrect.
3. Too much boost.
4. High engine temperature.
5. Oil entering the intake tract or cylinders.
6. Spark plugs too hot or gapped too wide.
7. Weak ignition system.
8. Carbon buildup in the combustion chamber.
9. Air charge is too hot.



related info and links

http://www.progl.com/General/detonation.htm

http://performancetrends.com/Engine-Analyzer-Pro.htm

http://kb-silvolite.com/article.php?action=read&A_id=38

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