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Old 02-03-2011, 07:53 PM
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Chevy 350 bottom end knock

I got a 5.7 liter Vortec engine that had a bottom end knock....I pulled it out & took the oil pan off & found that 1 of the rods had spun a bearing. I then checked the other rods & although the bearings were not spent, they were worn down. Of course the crank isn't perfect but it doesnt have any deep nicks in it either. I was wondering if I could go back w/ stock bearings or if I should use oversize bearings to maintain the correct oil pressure. Can someone please help poor peety???

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Old 02-03-2011, 08:39 PM
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Once it has spun a bearing, you can't just put new bearings back in, the journal that has spun will be ruined to the point of tearing up any new bearing you put in there.

The rod is trashed also, at the very least the big end is no longer round and of the correct diameter. The rod may be able to be saved by a machine shop if it isn't too bad, they will resize it to correct tolerances, or if it is too bad it will have to be replaced.

The crank may or may not be savable depending on how bad it is, the crank will have to be reground to the undersize the fully cleans up the surface on the spun journal. Only measurement will determine this, and the correct bearing size.
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Old 02-03-2011, 08:50 PM
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Thanks for the reply.....will I be able to tell w/ the naked eye that the rod is thrashed??? B/c this doesn't look that bad
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Old 02-03-2011, 09:45 PM
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There's also a good chance all the bearings aren't the same on all journals, I've heard the factory will mix uppers and lowers, in small size increments to achieve clearances due to variances in manufacturing.
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Old 02-04-2011, 01:19 AM
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Quote:
Originally Posted by peetyweet
Thanks for the reply.....will I be able to tell w/ the naked eye that the rod is thrashed??? B/c this doesn't look that bad
When you say "spun bearing" I take that to mean that the bearing shell has turned(maybe many times) in the rod big end bore. If that has happened you won't be able to tell rod bore size or bore hole roundness by looking at it. A couple thousandths of an inch is all it takes to mess things up. Same with the crank.

Any honest machine shop will tell you that when a bearing spins there is no easy fix. Parts have to be carefully measured(dial bore guage and micrometers good to .0001") and scored parts reworked as necessary.
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Old 02-04-2011, 04:58 AM
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Quote:
Originally Posted by peetyweet
I got a 5.7 liter Vortec engine that had a bottom end knock....I pulled it out & took the oil pan off & found that 1 of the rods had spun a bearing. I then checked the other rods & although the bearings were not spent, they were worn down. Of course the crank isn't perfect but it doesnt have any deep nicks in it either. I was wondering if I could go back w/ stock bearings or if I should use oversize bearings to maintain the correct oil pressure. Can someone please help poor peety???
I tried that once on a 283. Used some emory cloth, worked the crank and put new same size bearings in it. It only lasted a few months and spun a bearing again. Quick fix is a short time fix.
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