SB main bearing failure - Chevelle Tech
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  #1  
Old Jan 21st, 08, 11:56 AM
glennslanaker glennslanaker is offline
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Default SB main bearing failure

pulled my SB on a hunch something was wrong. i was running about 10psi oil pressure on an idle of around 700rpm's, but about 45 at 2500. this was with mobil 15-50 synth. anyway, two of the main bearings were nearly gone, worn to the copper and deeply grooved. this engine was completely rebuilt about 5 years ago and has been driven maybe 7-8k miles. i don't beat on it as a rule, it's never been hot, and so on.
the engine is a .030 over, 4 bolt, forged crank, '70 block. nothing else was too unusual except i also found the harmonic balancer had separated into two pieces. also i had for a couple years had coolant coming into two cylinders because of a cracked head. timing chain was fairly loose. it also seemed that there was gunk in the pan, black like oil, but more the consistancy of hot syrup. i have never used an additive, only mobil synth after break in.

question is, what could have caused this?
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  #2  
Old Jan 21st, 08, 12:00 PM
N20 GO N20 GO is offline
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Default Re: SB main bearing failure

Quote:
Originally Posted by glennslanaker View Post
pulled my SB on a hunch something was wrong. i was running about 10psi oil pressure on an idle of around 700rpm's, but about 45 at 2500. this was with mobil 15-50 synth. anyway, two of the main bearings were nearly gone, worn to the copper and deeply grooved. this engine was completely rebuilt about 5 years ago and has been driven maybe 7-8k miles. i don't beat on it as a rule, it's never been hot, and so on.
the engine is a .030 over, 4 bolt, forged crank, '70 block. nothing else was too unusual except i also found the harmonic balancer had separated into two pieces. also i had for a couple years had coolant coming into two cylinders because of a cracked head. timing chain was fairly loose. it also seemed that there was gunk in the pan, black like oil, but more the consistancy of hot syrup. i have never used an additive, only mobil synth after break in.

question is, what could have caused this?
Well a broken or bad balancer will take out the mains in a heart beat.
Your anti-freeze in the oil is very bad also.
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  #3  
Old Jan 21st, 08, 12:01 PM
pdq67 pdq67 is offline
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Default Re: SB main bearing failure

Donno??

There is a possibility that the damper going south coulda created some vibrations that mighta went down the crank to those two mains?

Maybe Mike or Carl as well as some of the other guy's will chime in. Bill...

Sorry, not much help...

pdq67
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  #4  
Old Jan 21st, 08, 2:03 PM
trmnatr trmnatr is offline
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Default Re: SB main bearing failure

Anit-freeze will eat the bearings up, THATS WHERE YOUR PROBLEMS STARTED
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  #5  
Old Jan 21st, 08, 2:36 PM
engineguy engineguy is offline
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Default Re: SB main bearing failure

As pointed out in previous posts, your problem was caused by coolant/antifreeze getting into the crankcase. Even small amounts of antifreeze will render any oil as totally useless. It is my guess that the main bearings that were most affected were at, or close to, the front of the engine (furthest from the oil pump).
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  #6  
Old Jan 21st, 08, 3:18 PM
RB69SS396Conv RB69SS396Conv is offline
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Default Re: SB main bearing failure

Also, very possible that there was debris left in the oil passages from some prior bearing failure; the passages weren't cleaned with a rifle brush or similar; and the debris eventually worked its way loose and found its way to the only place it can go.... right straight into the mains. Which is of course, consistent with "deeply grooved" (but not so much with antifreeze contamination): deep grooving is the hallmark of metal shavings.
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  #7  
Old Jan 21st, 08, 4:05 PM
Eric68 Eric68 is offline
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Default Re: SB main bearing failure

Quote:
Originally Posted by RB69SS396Conv View Post
deep grooving is the hallmark of metal shavings.
That's what I was thinking too.
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  #8  
Old Jan 21st, 08, 4:27 PM
glennslanaker glennslanaker is offline
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Default Re: SB main bearing failure

thanks for the replies, i think the metal shavings is as likely as anything. your saying that possibly the crank wasn't cleaned up well after machining?
i don't believe that a lot of coolant was getting into the oil, mostly it was vaporizing and going out the exhaust. i know the balancer was not helping matters, but i don't see how it would do the grooving in the crank/ bearings.
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  #9  
Old Jan 21st, 08, 5:05 PM
RB69SS396Conv RB69SS396Conv is offline
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Default Re: SB main bearing failure

No; I think the BLOCK wasn't cleaned up as thoroughly as it should have been.

I always pick up my block from the machine shop after they've been vatted and machined, but before cam bearings or ANY plugs have been put in; and I take it to the quarter car wash on a sunny day in the morning, along with a couple of cans of engine degreaser and a set of gun cleaning brushes. I run the rifle/piston/shotgun brushes through EVERY hole and passage to get rid of loose casting sand, debris from previous blow-ups that happened in the block, machining chips, etc. etc. etc., with plenty of degreaser to help disslodge anything lodged in oil build-up and varnish that might be left over; and let it sit out in the sun and dry all day. Then I paint it, put the cam bearings and plugs in, and oil the cyls, lifter bores, main saddles, etc. to prevent rust.

Coolant would have affected all 5 main bearings, and all 8 rods, equally, and would have made them ALL look like it was run without oil; heating, pitting, metal flaking off the bearings, etc. since antifreeze turns oil into something that doesn't lubricate. It doesn't produce gouges. A few bearings with deep scoring, and no generalized evidence in the rest of the motor of lack of lube, is evidence that the vertical oil feed passages to those particular mains, or the groove behind those cam bearings, had trash in them.
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  #10  
Old Jan 21st, 08, 6:46 PM
Troy70SS Troy70SS is offline
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Default Re: SB main bearing failure

I agree. The passages from the galley into those mains probably had trash in them and it's been doing damage since the day it was first started. I'll bet you will find all the bearings have minor damage from trash migrating but those mains started it and it migrated to the adjacent rods.

I've seen it before. The other stuff was all bad but not the smoking gun.

Had a buddy get his motor back from the machinist. When I stopped into his shop, he had the crank in it and all the pplugs in the motor. I say " Did you clean that thing already?" He says, "the machine shop washed it out for me and put in the freeze and galley plugs." I said - It's your money and your motor but I would pull all those galley plugs and clean it again. He chose not to. It didn't make it through CAM break-in before his oil pressure went to crap. I helped him tear it down and low and behold, he had one main bearing destroyed. The deep groove was in line and about the same width as the oil feed hole. The damage got less as you moved away from that bearing. It was ground zero. It also trashed the brand new stroker crank. I did the old "Hope you learned a lesson". I will never assemble a motor unless I clean it myself or trust the person who did with my life.

I was told years ago by a guy that had been doing this stuff longer than I had been alive. "You only get 1 chance to clean your parts" Some of the best advice I've ever received!

Sorry to hear about your issues. Good luck.
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  #11  
Old Jan 21st, 08, 6:56 PM
Wooderson Wooderson is offline
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Default Re: SB main bearing failure

A guy brought his engine to me to assemble, and I got almost a handful of crud out of the three oil galleys above the cam. If you don't run a wire brush through those long holes, you are asking for trouble. He had the block cleaned at a shop and it was supposed to be ready for assembly.
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  #12  
Old Jan 21st, 08, 7:20 PM
RB69SS396Conv RB69SS396Conv is offline
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Default Re: SB main bearing failure

Yup... the vat can't dissolve metal shavings. Just the tank by itself, is no guarantee.
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  #13  
Old Jan 21st, 08, 8:13 PM
BillK BillK is offline
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Default Re: SB main bearing failure

Glenn,
How about a few more details ? Which mains were worn ? A real bad out of balance situation show up a lot of times on # 2 and 4 mains. Most of the antifreeze damage I have seen looks like chunks coming out of the bearings, not wear down to the copper like you describe. How about some pictures ? I think you have something else going on that contributed to the problem.
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  #14  
Old Jan 21st, 08, 8:20 PM
HPseeker HPseeker is offline
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Default Re: SB main bearing failure

The oil filter bypass is blocked ?
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  #15  
Old Jan 22nd, 08, 1:27 AM
kirkwoodken kirkwoodken is offline
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Default Re: SB main bearing failure

Was your engine running very rich? Gas in the oil will thicken it up and it will stop pumping. How long since you checked or changed it? Just because it is not going out the tailpipe or running on the floor doesn't mean it can't disappear.
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