First pic of the autopsy

[socal pat]

What the heck could cause this? http://new.photos.yahoo.com/patgrowsit/photo/294928804378648488/0
I have run the motor through a bunch of cycles and can't see anything that could come in contact with that part of the crank!? BTW you are looking at a motor turned upside down, with the #1 piston at the lowest part of it's stroke.

[socal pat]

Here's a side angle though a bit blurry. http://new.photos.yahoo.com/patgrowsit/photo/294928804378648465/1

[Tom @ Fast Forward]

Is that what was causing your knock? Whatever it was, it must have been strong to make that cut?

[bogey]

I think that cut is from balancing the crank at the factory. The engine I tore down has the same machined cuts in a couple places.

[bogey]

The same cuts can be seen clearly here:

http://www.thebogarts.net/imagelib/Engine%20Replacement/DSCF0093.JPG

Such a lovely bearing that has been crushed flat!

[socal pat]

Obviously Bogey answered the question. I was looking all over the bottom end for some sign of wear or cause for my knock, and that was the only irregular thing I could find. So now it's on to the teardown. As soon as I have some good info I'll post again.

[bogey]

Grab the rod journal mounts and see if you can move them. Any movement at all on the crank is where the bad bearing is. Mine when click-clack as the shifted at least 1-2mm.

[Mathrips]

Plastigage each rod journal and main before the parts get moved around?
I want to know how a novice without an inside caliper checks the wrist pin tolerance. I have knocks of my own.

[socal pat]

Well...... no bearing damage. In fact the motor looks very healthy. Even the 110K mile old timing belt looks like new. No water pump leaks, cam seals or idler pulley issues. Just the one broken piston is all.

#1 piston has a chunk missing from the top. It must have spit it out of the exhaust because there is no sign of it anywhere. There is Zero scoring of the cyl. wall as well. The head honcho of the shop wasn't there when I dropped it off, but the guy I spoke with thinks that one cyl. got hot. As the ring swelled it closed its gap and whith no gap it had nowhere to swell and then pushed up to break off the top of the piston.
Where did the heat come from? That's the $64,000 question. I'm waiting for the shop owner to inspect and report what he thinks. I have some guesses, but I'll wait for someone more experienced than I to say.

[Kyp J]

I have heard that (knock, preignition, ping; pick one I never know which is which) causes the edges or chunks to be knocked off the piston. I had heat which scored and blackened all the pistons and cylinder walls but no chunks.

[socal pat]

Ok, the teardown is complete. On two of the pistons you can actually see where the ring ends butted against each other. With nowhere to go they tried pushing upwards and ended up damaging the thinest part of the piston. I was very specific about looking for a cause IE detonation, lean condition etc. No sign of either.
My machinist says he has seen identical damage in GM V8's when aftermarket SC's are installed. Of course it will vary from car to car depending on build tollerances, but if the ring gap is not wide enough to allow for swelling under heat then it is inevitable. He tells me that if I go back to the 105mm pulley I should have no problems. I mentioned the timing retard card and he loves the option. So no problems with the FFSC kit in and of itself. Just be careful when you start upgrading your pulleys. Any sign of ping means either get to a qualified tuner or "Back Off!"

[chuckerants]

Ok, the teardown is complete. On two of the pistons you can actually see where the ring ends butted against each other. With nowhere to go they tried pushing upwards and ended up damaging the thinest part of the piston. I was very specific about looking for a cause IE detonation, lean condition etc. No sign of either.
My machinist says he has seen identical damage in GM V8's when aftermarket SC's are installed. Of course it will vary from car to car depending on build tollerances, but if the ring gap is not wide enough to allow for swelling under heat then it is inevitable. He tells me that if I go back to the 105mm pulley I should have no problems. I mentioned the timing retard card and he loves the option. So no problems with the FFSC kit in and of itself. Just be careful when you start upgrading your pulleys. Any sign of ping means either get to a qualified tuner or "Back Off!"

Can you post a pic? I'm having a tough time visualizing what you're talking about - ring gaps and such.

[socal pat]

Sorry Chuck, but I didn't have my camerea with me when I went in yesterday. He'll be starting with my headwork so maybe I can swing by next week and get some pics for you.

[cmetzner]

. Just be careful when you start upgrading your pulleys. Any sign of ping means either get to a qualified tuner or "Back Off!"


Did you hear any ping or have any other symptoms before the engine let go? If so, was it constant or intermittant?

I ask because I run a 115 pulley. Since I ran some Seafoam through, I do not get any ping. Previously, I had to pull 6* of timing by way of the SS controller to avoid ping.

I still pull 2* just to be conservative but I do not hear any ping with the stock timing.

[socal pat]

I was getting some ping after 3-4 consecutive hard runs from a stop to the middle of 4th gear. Maybe I was getting heat soak? Anyway I was running Toluene to make ~94 oct. I am sure if I could have pulled a couple degrees of timing it would have stopped the ping. My ping was never a knock-type. It sounded like shaking a small metal box with some coarse sand in it. Truth be told I wasn't terribly afraid of going to the edge. I was lusting after some lower compression pistons anyway. Besides it was time to pull the head for a valve job too.