What caused this engine damage

[joetiii]

So I am tearing down a 3.0 to rebuild. The engine had bad compression in one cylinder and leak down on another was out of whack. When I pulled off the exhaust I noticed one of the valve guide ends had cracked and broken off. Does this happen often?



I had my fingers crossed that the missing piece just dropped down into the exhaust though I didn't hear anything rattling around in the headers.

I pulled a plug on another cylinder and noticed some half baked molasses on the tip.




I just pulled the cylinder off said piston and this is what I found......




The cylinder walls were not scored at all. Question is what do you suppose caused this? Metal fatigue?

[Dave 86 930 Fl]

Turbo motor?

[blucille]

impact from a fall at speed?

[joetiii]

Its a 3.0 NA engine with 60k on a rebuild.

[joetiii]

Originally Posted by sonett43

impact from a fall at speed?

Lew.... wrong engine.

If this project does not get complete before May, my rock solid, twice hardened engine mount bolts are resting peacefully awaiting 5 mountain passes.

[blucille]

Originally Posted by joetiii

Lew.... wrong engine.

If this project does not get complete before May, my rock solid, twice hardened engine mount bolts are resting peacefully awaiting 5 mountain passes.

I knew...that's why I gave you a smilie.

[rsscotty]

Looks to be detonation. Do you recall what your ignition timing is set to at full advance?

What is the heat range number on your spark plugs?

What type of fuel have you been using?

[scarceller]

Stress cracks from mild detonation? Pistons and rings are often damaged in those areas from detonation.

You sure your ignition timing is correct? Your distributor may be over advancing timing during WOT.

Also looks like engine is tired and pulling in oil, those piston tops look like oil is burning during power stroke.

[Kevin Stewart]

looks like a piece of valve guide broke off and went through the motor any marks on the head, Kevin

[Flat6pac]

And 24 dilivar studs...?
Bruce

[cgarr]

That guide should have been blown out the exhaust. Only time I have seen cracked guides is when a valve gets hit and bent.

Looking a it again, check your other heads exhaust valves. I have seen some when the guide is seated rather deep as yours kind of looks like the bulb where the valve starts to taper out at the stem can hit against the guide and split it out.

[Steve@Rennsport]

Originally Posted by rsscotty

Looks to be detonation. Do you recall what your ignition timing is set to at full advance?

What is the heat range number on your spark plugs?

What type of fuel have you been using?

Detonation, for certain,....

Those OEM cast pistons don't take that for long.

Scotty asks a bunch of good questions that may lead to why this happened. I'd be wondering about AFR's, too.

With 60K on the rebuild, I'd also be wondering about how much deck height that engine had,...........

[joetiii]

Looks to be detonation. Do you recall what your ignition timing is set to at full advance?



What is the heat range number on your spark plugs?



What type of fuel have you been using?

Unfortunately, I was not running this engine before it was dropped so I have no idea what the timing was set at or what gas was used. Claims were that it might have euro P&Cs with higher compression.

[joetiii]

And 24 dilivar studs...?

Bruce

Yeah that's what I thought.....the magnet sticks to all of em.

[psalt]

joetiii,

BA has photos of 3.0 pistons with the same damage in Excellence technical notes. Guess what, Euro 9.8's..... The guess was broken rings from detonation, broken lands from running with broken rings.

CIS, especially with vacuum leaks, runs lean under load and the later SC's ran very retarded timing, low 20's BTDC, to prevent this kind of thing. Push up the compression with pistons designed for 98 RON fuel and bump up the timing and there you go. Especially with the later small port and small runner engines that boost low speed VE. Same thing with turbo kit SCs, there is a reason the factory went to forged pistons in the turbo.

If the engine was rebuilt, my guess on the valve guides is that someone drove an O/S guide into the wrong press fit at the wrong temperature. I would take them all out .

[SCOTITUDE]

pics from my first rebuild. dizzy came loose screwing the timing. Detonation damage. look familiar?

[Walt Fricke]

If the heads were refaced as part of the rebuild, and that was not compensated for by increasing the thickness of the cylinder base sealing copper ring, that would increase the CR. Could be a problem, especially if combined with higher CR Euro pistons. I assume you don't have evidence of the piston hitting the head, but the CR might have gotten even higher than expected due to that.

If you have access to a burette, measuring the CR during a rebuild turns out to be pretty easy. You can skip measuring the various parts, and just measure the volume at TDC while you are reassembling the motor. Just takes installing one piston, cylinder, and head after you have completed the short block. That way you can measure, make a change, measure again. You already know the displacement, so with the TDC volume you have all you need.

[joetiii]

Originally Posted by Walt Fricke

If the heads were refaced as part of the rebuild, and that was not compensated for by increasing the thickness of the cylinder base sealing copper ring, that would increase the CR. Could be a problem, especially if combined with higher CR Euro pistons. I assume you don't have evidence of the piston hitting the head, but the CR might have gotten even higher than expected due to that.

If you have access to a burette, measuring the CR during a rebuild turns out to be pretty easy. You can skip measuring the various parts, and just measure the volume at TDC while you are reassembling the motor. Just takes installing one piston, cylinder, and head after you have completed the short block. That way you can measure, make a change, measure again. You already know the displacement, so with the TDC volume you have all you need.

Yup Walt, you bring up a task I was was already planning during the rebuild .

Since I've got the case opened up, its a little too late to go back and get a deck height measurement like Steve suggests. Though I am curious if my machine shop should be measuring something in particular?

Wayne's book only gives part #s for complete P&C sets. Is there anyway to cross reference the casting numbers on the pistons to see if in fact they're Euro P&C's?

i can read 95L67 on one side and c021 on the other side of each piston