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Old 01-24-2010, 05:36 PM
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Main bearing question

I took apart my Olds 350 after I have drag race it for about 1 ˝ years I found the number 4 main bearing looking eat up and won’t stay in place on the cap or the block the crank had grooves in it also I also found the number 7 piston had a broke ring the top ring the rod bearings for 7+8 also show more wear then the others. Could this broken piston ring cause the bearing problem?
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Old 01-24-2010, 06:29 PM
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Without seeing the bearings, I would think something got into the #4 bearing, grooved the crank and ate up the insert, dropping oil pressure to the other bearings....causing more wear on them.
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Old 01-24-2010, 06:50 PM
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here is a picture of the main bearings.the one on the left is the block side bearing
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Old 01-24-2010, 10:19 PM
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To me it looks like Detonation is the root cause. Detonation will break a ring, causing poor oil control and making the detonation worse, which beats up the rod bearings and the main bearings on either side of the affected piston. The main bearing you pictured shows signs of overheating causing delamination (flaking) of the babbit layer. Detonation will also pound the bearing bores and bearing shells causing the bearing shell to loose its tight fit to the housing bore.

You will need to look at other aspects of the entire engine to piece together the whole puzzle- compression ratio and fuel used, timing curve, engine temps and usage prior to the event.

68NovaSS could also be right, the main bearing overheated or was scored(hard to say which was first) and led to damage at the rod bearings due to the mains oiling the rods.

Are the bearings still tight in the #7 and 8 rod big ends??

Was the engine fresh rebuilt 1 1/2 years ago, bored, rods resized, crank reground, etc?

More you can tell us about the whole engine the better the chances of figuring out what happened first.
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Old 01-25-2010, 12:07 AM
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Quote:
Originally Posted by hotrod688
here is a picture of the main bearings.the one on the left is the block side bearing
Ordinarily you wouldn't expect to see full grooved bearings, w/oil holes in both halves. It looks like a pair of uppers...

You'd expect the damage from detonation to be seen more on the bottom bearing half, but in any event, the bearing has definitely seen some hard use to cause that much surface fatigue.
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Old 01-25-2010, 03:11 AM
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(You will need to look at other aspects of the entire engine to piece together the whole puzzle- compression ratio and fuel used, timing curve, engine temps and usage prior to the event.) Stock piston 8.5 compression, 93 octane, 24 or 25 base timing with 20 degree advance, engine had run hot due to throwing the belt but I did install a electric water pump drive after it did this 5 or 6 times this motor was drag raced only.

(Are the bearings still tight in the #7 and 8 rod big ends??) Yes they are.

(Was the engine fresh rebuilt 1 1/2 years ago, bored, rods resized, crank reground, etc?) Yes cylinder was honed, nothing done to the rods and the crank was a reconditioned one with bearings.
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Old 01-25-2010, 05:05 AM
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If that's not a typo, or includes the vacuum advance, that's too much timing, IMO.
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Old 01-25-2010, 05:07 AM
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bearings

Can you post pictures of the other rod and main bearings

Do you have the clearance of that main recorded some place? or remember what it was??

Cast or steel crank??

IMO i really don't like those timing numbers. That would be 45 degrees total timing and if not verified some how at max RPM could be alot more.

What do the plugs look like, can i see a picture of them??



Keith
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Old 01-25-2010, 07:57 AM
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Timing for an Olds should be 36-38 degrees max.

Looks like detonation, improper clearences, and the posibility that the crank bores arent aligned.

If youre using the original factory pistons and an aftermarket head gasket, and no milling to the head or block, you have much less than 8.5 to 1
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Old 01-25-2010, 10:57 AM
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guys, this is a good friend of mine, this is the only journal with damage. the vacuum advance has been disconnected. the plugs up till he pulled the motor were fine. it has a 750 cfm doubble pumper on it with the jetting close to what the carb came with from the box. its only got a mild cam, from crane.
this engine is out of a 72 olds cutlass and was cherry inside. he had to replace the crank because the origional had spun the old balancer, so the crank is the only unknown source. and came with journals when he bought it.
we did not measure every journal to make sure all was well, and that could very well be the reason theres problems. just looking for other ideas on the possibilities of what it could be.
when he first got the car going and the weather warmed up last year, he did have some overheating going on, and the carb was too rich at the time.
its been jetted down till the plugs quit being wet or sooty.
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Old 01-25-2010, 11:17 AM
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Quote:
Originally Posted by tnsmith10
guys, this is a good friend of mine, this is the only journal with damage. the vacuum advance has been disconnected. the plugs up till he pulled the motor were fine. it has a 750 cfm doubble pumper on it with the jetting close to what the carb came with from the box. its only got a mild cam, from crane.
this engine is out of a 72 olds cutlass and was cherry inside. he had to replace the crank because the origional had spun the old balancer, so the crank is the only unknown source. and came with journals when he bought it.
we did not measure every journal to make sure all was well, and that could very well be the reason theres problems. just looking for other ideas on the possibilities of what it could be.
when he first got the car going and the weather warmed up last year, he did have some overheating going on, and the carb was too rich at the time.
its been jetted down till the plugs quit being wet or sooty.
If the plugs and bearings could be photoed in order, like K-Star suggested, the possibility might be narrowed down- like if the crank wasn't true, or there were journals out of round or tapered, etc. (things that YOU would have picked up on, no doubt), but barring that, the actual cause might never be known w/100% certainty.

But I'd think a rebuild should include a line hone to remove that as a possibility; even if the block was perfect, it might not be now.

A bore hone, maybe fresh rings, good bolts and resizing the rods, a fresh crank (and the roll it takes to make all this happen ) will hopefully have it squared away.
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Old 01-26-2010, 03:51 AM
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at this time, i know hes taken some snap shots (he showed them to me last nite) of the bearings like you asked, but as far as the plugs go, your not going to get a true reading from them as he ran the car for just enough time to get it up the hill and into the garage to pull the motor.
so the plugs are black and sooty from pumping the thing to death to get it to stay running enough to get it into the garage (it sat for over a month without starting and the weather here has been colder than normal and theres no choke on the carb).
1 of the other things that weve considered is that the bearings were not correct for the crank as he went through all the journals and measured them and found them all within specs.
when he and i talked about it last nite, he is going to have the block checked over and the crank as well to be sure that everything is in line, and do what is necassary to correct the issue.

on a side note, this olds engine was fabricated into a 93 camaro with a th350 that i built and was running 8.30's (1/8th mile) late last year, and hes hoping with some flat tops, and some head work and a better stall converter to get down into the 7's, or quick enough to beat a jr. dragster. lol
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Old 01-26-2010, 04:53 AM
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engine

I am not interested in the lean/rich readings of the plugs. I am interested in the detonation reading of the plugs. That is why I asked what they looked like. I am assuming that the engine had some detonation going on. The detonation will show regardless of the lean/rich condition.

IMO, with out all the pre-damage data you are never going to get a 100% reason for the failure. I have been doing this a long, long time and assessing damage is a real art, and rarely diagnosed correct.

The bearings look like they suffered from a loss of oil, caused by to small a clearance, but with out knowing the sizes thats just a stab in the dark.

IMO, not caused by detonation, but again I have seen detonation do some real crazy things inside an engine. if the plug reveal serious detonation, then that might be where the damage came from. The rod bearings should show signs of a beating if it was detonation, also the under side(oil pan side) of the piston tops should be oil burnt looking.

Keith
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Old 01-26-2010, 03:36 PM
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Here is a link to some pictures
http://s242.photobucket.com/albums/f...20Pics%202010/

Last edited by hotrod688; 01-26-2010 at 03:42 PM.
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Old 01-26-2010, 04:13 PM
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Quote:
Originally Posted by hotrod688
Way too hard my link just goes to some generic place, put 'em here so we don't have to spend time hunting.

Question back to the very beginning. The picture shows two inserts with grooves on each. Is this an upper and lower on one bearing, or uppers of two different bearings. If an upper and lower of one bearing which was where.

The reason for this question is that decades ago, when the term "GROOVY" was in style, using grooved inserts top and bottom or grooving the crank was considered the hot set up to insure continuous oiling of the rod bearings. Unfortunately we quickly found it disrupted the oil wedge of the lower main which reduced the bearing's carrying capacity and that proved to be abigger problem than flying rods. The lower is the side that takes the biggest beating with combustion forces and gravity working against the oil wedge and trying to shove the crank out the bottom.

But frankly this looks a lot like a structural failure of the material. Why, is the question? That can range from a manufacturing error, to the oil wedge prying a chunk of the over-plate out. What does the crank journal look like? This doesn't appear to have become hot, nor does it really look like it lost the oil wedge, it looks like the over-plate wasn't sticking to the substrate so it peeled off.

Bogie
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