they are still in the block.. i'll rotate the crank and get a picture of the crown now thanks.

 

added these photos to first post. is that some pitting i see in head bowl cyl 1?

P1








P4





H1

 

Valve guides cannot be the cause of the leakdown.Leakdown is performed on the compression stroke and the valves are sealed if they aren't bent that is and no air should reach the ports.

Detonation was induced from the oil that was introduced to the cylinder.
Sounds to me like the oil was dripping off the exh guides because it was being pushed out on the exh stroke from the cylinder.

 

Looks like detonation to me. I feel though that more than likely the oil usage is from ring seal.

 

thanks for the comments. couple of questions.

are you saying the dripping valve guides are not significant enough to cause the majority of the oil burning issue?

what evidence are you looking at that confirms det to you?

 

2 pistons form two engines suffering similar fate.
pic1= exhaust side of pistons
pic2= intake side
pic3= top of piston.

important notes. exhaust side of piston looks great. top of pistons look great. a/f looks plenty rich at 10.8/1. Skirts look great indicating sufficient wall clearance.

Intake side of pistons above top ring land is where detonation starts. the mahle piston on top suffered less detonation. looks like it was sand blasted . bottom piston is one step farther and piston has started melting. Bottom piston would have cylinder wall that looks like pics in post #1

 

Good pictures and good explanation, Nothing to add there.

Mark

 

[QUOTE=94AWDcoupe]2 pistons form two engines suffering similar fate.

important notes. exhaust side of piston looks great. top of pistons look great. a/f looks plenty rich at 10.8/1. Skirts look great indicating sufficient wall clearance.

Intake side of pistons above top ring land is where detonation starts. the mahle piston on top suffered less detonation. looks like it was sand blasted . bottom piston is one step farther and piston has started melting. Bottom piston would have cylinder wall that looks like pics in post #1


thanks for those pics and explanation. probably see the same thing once my pistons are out.

so about the chicken and egg. detonation lead to poor seal, then oil and more detonation. or leaky valve guides introduced oil causing detonation and poor seal adding more oil. probably can't be determined.

 

You asked me to comment, so here is mine:

Unless there is an obvious problem with a valve (and there does not appear to be so), the leakdown issue is almost certainly caused by poor ring seal.

As for the root cause, the answer may not be apparent until/unless the piston assembly in question is removed and inspected, and all clearances and such are carefully checked.

What we do know is that poor oil control due to a ring issue will pass oil into the cc, and oil fouling will create a preignition issue as certain as death and taxes.

 

[QUOTE=Ted B]You asked me to comment, so here is mine:
QUOTE]
thanks for the comment, and i hope you weren't forced .. hopefully we will find out in a month when i get back to tearing the rest of that motor apart.

 

If you want to tell exactly where the compression is leaking from, do a leakdown test.

All of those problems can stem from excessive heat in that cylinder. That causes the piston to expand more which will wear the cylinder walls and rings. The heat will also cause the guides to wear, then the extra clearance when the engine is cold will pull oil past the seals (which are probably worn) and into the cylinder. That combined with the worn rings is where your oil consumption is coming from. Heat and oil in the chamber will lead to more detonation.

 

With lower compression in a cyl (or one too high), oil can also be pumped through PVC into combustion assisting existing oil induced autoignition.

 

*****FIND PART TWO OF THIS THREAD HERE https://www.evolutionm.net/forums/ev...e-pistons.html ************