why would a main bearing chew itself up like this?
12-10-2007, 10:27 PM
#1
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why would a main bearing chew itself up like this?
after putting it off for a year I finally pulled my stock LT1 out of the car. The engine seized just shy of a year ago after I put it back in, replacing my blown 383. I couldn't turn over the crank so I could only get two pistons out tonight, then I popped all the main caps off. some things I noticed:
The two pistons I removed, the top rings broke on each of those. Im assuming its because I wasn't exactly kind to them while removing. the engine did have some blow by before I pulled it out a few years ago to put the 383 in. Could this have been the cause or would broken piston rings cause a much more serious problem?
On each of the pistons, the wrist pins are VERY tight. it takes some force to move the piston on the rod. Is this because they are press fit? my 383 rods/pistons weren't like this, because they were floating pins?
With the exception of the #5 main all the journals of the rods/mains I took off looked OK. bearings showed quite a bit of wear but no damage was done.
The #5 main bearing seems to have chewed up its inner edge. the rest of the bearing is fine. what could have caused it to do this? I never had the engine apart although I did replace the rear main seal while it was out. Could I have harmed something while doing this?
any tips for getting the crank to turn so I can get the other pistons out? lol
I really don't know why it did this. it didn't leak or burn oil for the little bit it ran after I put it back in.
Oh well, I got the pieces off that I needed for the new engine... heads, oil pump, etc. just wanted to figure out why it blew.
on to the pictures!
#5 main journal all torn up.
130,000 mile stock heads.
two pistons still in the block (they're oddly colored because I'm shining a flashlight on them.)
mess
The two pistons I removed, the top rings broke on each of those. Im assuming its because I wasn't exactly kind to them while removing. the engine did have some blow by before I pulled it out a few years ago to put the 383 in. Could this have been the cause or would broken piston rings cause a much more serious problem?
On each of the pistons, the wrist pins are VERY tight. it takes some force to move the piston on the rod. Is this because they are press fit? my 383 rods/pistons weren't like this, because they were floating pins?
With the exception of the #5 main all the journals of the rods/mains I took off looked OK. bearings showed quite a bit of wear but no damage was done.
The #5 main bearing seems to have chewed up its inner edge. the rest of the bearing is fine. what could have caused it to do this? I never had the engine apart although I did replace the rear main seal while it was out. Could I have harmed something while doing this?
any tips for getting the crank to turn so I can get the other pistons out? lol
I really don't know why it did this. it didn't leak or burn oil for the little bit it ran after I put it back in.
Oh well, I got the pieces off that I needed for the new engine... heads, oil pump, etc. just wanted to figure out why it blew.
on to the pictures!
#5 main journal all torn up.
130,000 mile stock heads.
two pistons still in the block (they're oddly colored because I'm shining a flashlight on them.)
mess
12-11-2007, 06:29 AM
#2
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Location: Lexington Park, Maryland, USA
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Detonation causes all of what you describe.
Detonation probably broke the rings and pounded the bearings.
Piston rings can break and sometimes it's hard to notice, (you'll see blowby).
The pin being tight on the piston is due to detonation. (pounding of the aluminum around the wrist pin).
We've all had motors that look like yours so don't feel too down.
Edit add: I just looked at your thrust bearing and that could be chewed up from a bad torque converter (if you are an A4) or improper instal of the torque converter.
Karl
Detonation probably broke the rings and pounded the bearings.
Piston rings can break and sometimes it's hard to notice, (you'll see blowby).
The pin being tight on the piston is due to detonation. (pounding of the aluminum around the wrist pin).
We've all had motors that look like yours so don't feel too down.
Edit add: I just looked at your thrust bearing and that could be chewed up from a bad torque converter (if you are an A4) or improper instal of the torque converter.
Karl
Last edited by quickSS; 12-11-2007 at 08:37 AM.
12-11-2007, 10:11 AM
#3
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Detonation causes all of what you describe.
Detonation probably broke the rings and pounded the bearings.
Piston rings can break and sometimes it's hard to notice, (you'll see blowby).
The pin being tight on the piston is due to detonation. (pounding of the aluminum around the wrist pin).
Detonation probably broke the rings and pounded the bearings.
Piston rings can break and sometimes it's hard to notice, (you'll see blowby).
The pin being tight on the piston is due to detonation. (pounding of the aluminum around the wrist pin).
How could the converter be installed wrong?
12-12-2007, 08:37 AM
#8
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haha, neither happened! to my knowledge this car has never seen spray, or at least not in the 4 years I have owned it. I guess its a good thing this happened because I would probably tried to stick a cam in this engine and by how it looks now I wouldn't have gotten very far.
12-12-2007, 08:53 AM
#9
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Location: LA (lower Alabama)
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The only way ring lands get broken and wrist pin holes get smashed is through severe detonation. Don't think bad gas would do it as ya probably could have heard it. Maybe ya did hear it and didn't know what it was!!!!!!
Gas may have had water in it too but that would have caused a big miss and no power.
It could have been running with the broken lands for a long time as some do. Then an accumulation of things locked it up.
Spraying may have been why the previous owner got rid of it.
Gas may have had water in it too but that would have caused a big miss and no power.
It could have been running with the broken lands for a long time as some do. Then an accumulation of things locked it up.
Spraying may have been why the previous owner got rid of it.
12-12-2007, 01:13 PM
#10
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I just realized I never cleaned the ridge off the top of the cylinders before I removed the pistons.
I know what detonation sounds like, my '68 bonneville pinged BAD when I had to put 91 octane in it one day
the previous owner was a dealer and before that it was female owned. I highly doubt the car was sprayed. it was bone stock minus a K&N air filter.
I know what detonation sounds like, my '68 bonneville pinged BAD when I had to put 91 octane in it one day
the previous owner was a dealer and before that it was female owned. I highly doubt the car was sprayed. it was bone stock minus a K&N air filter.
12-22-2007, 03:46 PM
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pulled the rest of it apart...
the block is still good. would need some work though to get it usable again. it definitely lost oil pressure, every bearing is spun. not sure why the one piston is scuffed up and all the others are not. oh well, time to send the heads out to see if they're still good and have them freshened up.
the block is still good. would need some work though to get it usable again. it definitely lost oil pressure, every bearing is spun. not sure why the one piston is scuffed up and all the others are not. oh well, time to send the heads out to see if they're still good and have them freshened up.
