Cracked piston...$^*#@!!!
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Good catch, u saved your engine.
Here are some pics. The cracks are just inside the black marker lines.
http://forums.corvetteforum.com/album.php?albumid=25340
http://forums.corvetteforum.com/album.php?albumid=25340
Regardless of your replacement choice u need to match piston weights.
Great effort,
cardo0
Thread Starter
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,210
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Wow, just in time as that engines life was nearly over. A broken piston can turn a block into scrap in a second. Curious though it makes me wonder too if the valves somehow struck the pistons dome or detonation from too hi c.r.. As long as its out now u could try and polish out the cracks to see how deep they are.
Regardless of your replacement choice u need to match piston weights.
Great effort,
cardo0
Regardless of your replacement choice u need to match piston weights.
Great effort,
cardo0
Nope. It was running normal. No oil burning. Car was running strong.
My guy at work couldn't see any telltale signs of detonation which is what I was suspect of to cause the cracks. I think I will contact KB and send them the pics and the piston if they want to analyze it. Warranty is long over but it may help them out if cracking is rare for this type of piston.
Last edited by resdoggie; Apr 10, 2012 at 06:47 PM.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
Thread Starter
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,210
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Update
I emailed KB regarding the (unusual) cracks in the piston. Here is their response:
Mike,
Have not seen a crown crack like this. We may get a better idea if we saw
the piston. You can send it to the address below to my attention. We will
have to cut it into sections to better look at the cracks.
A single may be available. Forward the gram weight for the piston and pin
only, part number and oversize.
Best regards,
Marko
United Engine & Machine - Icon - KB Performance - Silvolite - KB VTwin
Motorcycle
1040 Corbett St.
Carson City, NV 89706
I made it clear to KB that I was not seeking any warranty (17 years later and 15K miles) but just wanted to know if they could determine the cause so I could take steps to prevent this from happening again. I'll have the piston in the mail next week. I'll let you all know the results when KB gets back to me.
Mike,
Have not seen a crown crack like this. We may get a better idea if we saw
the piston. You can send it to the address below to my attention. We will
have to cut it into sections to better look at the cracks.
A single may be available. Forward the gram weight for the piston and pin
only, part number and oversize.
Best regards,
Marko
United Engine & Machine - Icon - KB Performance - Silvolite - KB VTwin
Motorcycle
1040 Corbett St.
Carson City, NV 89706
I made it clear to KB that I was not seeking any warranty (17 years later and 15K miles) but just wanted to know if they could determine the cause so I could take steps to prevent this from happening again. I'll have the piston in the mail next week. I'll let you all know the results when KB gets back to me.
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Drifting
Joined: Aug 2005
Posts: 1,443
Likes: 65
From: Wauconda IL
Wild.. Not at all what I expected to see.
With where the cracks are, it almost looks like on either side of the rod?
If this were a marine engine, I'd say hydro-lock but in a street engine, no clue...
With where the cracks are, it almost looks like on either side of the rod?
If this were a marine engine, I'd say hydro-lock but in a street engine, no clue...
Advanced
Joined: Dec 2006
Posts: 50
Likes: 1
From: So. Cal. CA
What were the results of your tests?
Did they indicate how deep the cracks are? I'm curious because they're relatively parallel -- almost like something was in there and maybe scratched the surface. Did you ever use something to try to find TDC in that cylinder, or stick something else in there? Or maybe they got slightly scratched before installation, and the scratch shows up better after all this time and wear?
Mike
Mike
Thread Starter
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,210
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Did they indicate how deep the cracks are? I'm curious because they're relatively parallel -- almost like something was in there and maybe scratched the surface. Did you ever use something to try to find TDC in that cylinder, or stick something else in there? Or maybe they got slightly scratched before installation, and the scratch shows up better after all this time and wear?
Mike
Mike
J/K. AFAIK the piston was fine when I put it in 17 years ago.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
I emailed KB regarding the (unusual) cracks in the piston. Here is their response:
Mike,
Have not seen a crown crack like this. We may get a better idea if we saw
the piston. You can send it to the address below to my attention. We will
have to cut it into sections to better look at the cracks.
A single may be available. Forward the gram weight for the piston and pin
only, part number and oversize.
Best regards,
Marko
United Engine & Machine - Icon - KB Performance - Silvolite - KB VTwin
Motorcycle
1040 Corbett St.
Carson City, NV 89706
I made it clear to KB that I was not seeking any warranty (17 years later and 15K miles) but just wanted to know if they could determine the cause so I could take steps to prevent this from happening again. I'll have the piston in the mail next week. I'll let you all know the results when KB gets back to me.
Mike,
Have not seen a crown crack like this. We may get a better idea if we saw
the piston. You can send it to the address below to my attention. We will
have to cut it into sections to better look at the cracks.
A single may be available. Forward the gram weight for the piston and pin
only, part number and oversize.
Best regards,
Marko
United Engine & Machine - Icon - KB Performance - Silvolite - KB VTwin
Motorcycle
1040 Corbett St.
Carson City, NV 89706
I made it clear to KB that I was not seeking any warranty (17 years later and 15K miles) but just wanted to know if they could determine the cause so I could take steps to prevent this from happening again. I'll have the piston in the mail next week. I'll let you all know the results when KB gets back to me.
Well i hope to read of results from KB. I think we all need/can use the education here.
Thx for the updates resdoggie,
cardo0
Thread Starter
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,210
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Final update
I took the piston to a local automotive machine shop last week to remove the pressed in pin so I could ship the piston sans rod to KB for their analysis. The local shop inspected the piston and said it was definitely a scratch. They also said that hyper pistons don't crack - they break, period. Alright, so I had a dye penetrant test done. Negative results. It was also put under a microscope and it clearly showed that they were scratches. Well, it sure looked like a crack.
The good news is I can put it back in the engine for another season. Next year I will pull the engine and put in a 383 stroker rotating assembly.
The good news is I can put it back in the engine for another season. Next year I will pull the engine and put in a 383 stroker rotating assembly.
Le Mans Master
Joined: Jan 2006
Posts: 6,503
Likes: 138
From: Butler Pa
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Thatt'a boy Bash.
Wow, do pictures lie or what?
Good news for resdoggie and thx for posting all this.
Just hone, re-ring and brg now?
Man this turned out to be a pretty cool thread on pistons,
cardo0
Good news for resdoggie and thx for posting all this. Just hone, re-ring and brg now?Man this turned out to be a pretty cool thread on pistons,
cardo0
Thread Starter
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,210
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Melting Slicks
Joined: Jul 2006
Posts: 2,275
Likes: 483
From: Salmon Arm, BC
I just went back and looked at your pics again. Now that we know they are only scratches on the piston, I assume you used clay on this piston to check for your piston to valve clearance.....and then sliced the clay down the middle to measure your clearance after peeling half of the clay away.......did I guess right?
Le Mans Master
Joined: Dec 2006
Posts: 5,557
Likes: 9
From: Oquirrh Mountains
St. Jude Donor '09
======================================== =================
Interesting thread.
Thread Starter
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,210
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
I just went back and looked at your pics again. Now that we know they are only scratches on the piston, I assume you used clay on this piston to check for your piston to valve clearance.....and then sliced the clay down the middle to measure your clearance after peeling half of the clay away.......did I guess right?