Replacing the rear seal so I thought I would check front main and the 2nd . The front and rear mains show some polished rings and I can't feel any groves . The 2nd one back is perfectly smooth but the bottom part of the of the bearing is kind of a gold color where the rest is silver . What does this mean if anything . Engine rebuilt 12yrs ago ,20000 miles .

 

Take a look at this, should help you out.

http://engineparts.com/publications/CL77-3-402.pdf


Scott

 

Thanks Scott

The closest one to what I am seeing is the normal one , the only difference is the gold discoloring

Thanks Rob

 

The 'gold' coloring sound like that initial wear layer of the bearing is just strarting to get worn through (thin coating of lead/tin for break-in). If so, there's no need to do anything but put a smear of lube on the bearing in those caps and install them just as they were (same journal...same orientation).

 

Looks like you've worn through the first of the 3 layers on the conventional tri-metal bearing shell.

If it would ease your mind, you could check the clearance using Plastigage.

We don't know if you did this or not, but marking a bearing cap--whether it be for engine mains, con rods, or differentials--before disassembly with a series of punch marks or an actual number stamp guarantees that it will go back in its correct position, which is vital.

 

A picture speaks 1,000 words - but there should be no color other than silver showing. The initial sacrificial coating is a light, dull zinc. You're into the bronze/copper backing of the bearing, and that's a serious problem

If it's just in the center, that's a clear indication the machine shop didn't do their job as main bearing bore isn't round. Is the bearing significantly less shiny at the parting line - the ends of the bearings where the two halves meet?

I'd say that before you do anything, get a picture and post it. This seems pretty clear, but as the solution is a teardown I sure wouldn't go that far until folks here have seen exactly what you're seeing.

 

Sealed Power says:

"Federal Mogul CP-Series rod bearings feature classic tri metal construction and are a good choice for either street or moderate competition use. They have rugged 1010 steel backings covered by Federal Mogul's H-24 copper-lead alloy. On top of this is a nickel barrier, followed by the tri metal lead-tin-copper overplate that gives these bearings their strength and fatigue resistance. The bearings are then entirely covered with a flash coating of tin."

If the OP's bearings are the same construction, I would say only a partial wearing of that flash coating of tin has occurred. If the clearance is still within spec, he's good to go.

 

Regardless of where he's at in the bearing - and we disagree on that - the fact that the wear is occurring in a band vs. across the bearing indicates that the main bearing bore is not round - and that is a problem.

A picture would be a big help

 

That 'band of wear' in the middle of the bearing is merely showing where the higher load are on that bearing. No surprise....it's in the UP/DOWN direction, so the most wear (but very small wear as it is only through the lead/tin 'initial break-in' layer) is in the middle of the bearing. Not a problem.

 

My experience has been when blocks/rods are true as in honed or line bored and balanced then my bearing surfaces have even wear accross the face of the bearings. Copper has always, to me, indicated a wear issue especially if it is in one particular spot. OP's engine might continue to run for some extended period of time but I'd op for safe vs sorry. Of course, how used makes a big difference. Just my 2 cents.

 

Have you ever actually seen a used main bearing in a GEN I 350? There is no "up and down" movement - the crank rides in a "bearing" of oil that is evenly distributed around the bearing. There is usually a slight lesser wear pattern at the parting line - but otherwise wear is distributed across the bearing...if the proper bearing crush was achieved and the bore was round. This is how bearings work...

If the wear isn't even across the face - in either direction - it's indicative of a main bore that isn't the right size, or isn't aligned.

These are rod bearings I removed from a GEN I 350 with about 80K miles that had blown a head gasket but was driven until main bearing failure. Ignoring the pitting that is endemic to that type of failure - does anyone see an uneven wear pattern?

 

Thanks for all your info and input . I have taken the main and connecting rod bearing to a local engine shop . At this point of having the motor torn apart with the questionable bearings I can see myself putting an easy $600 into motor. I think I will let the boys at the engine shop do a full rebuild and have every thing fresh .

 

Let us know what the machine shop thinks of the bearings - is it the same shop that did the rebuild 20K miles ago??

 

If you have any doubt at all you should plastigage them Any indication/suggestion that you are through the top layer warrants a confirmation of the clearance.

I can't count the number of bearing shells I've seen in my lifetime. I've never seen bearings worn "evenly". The bottom shell will almost always be worn out and the top one probably reuseable. The load is downward and creates a wear band at the lowest point across the shell (front to back). The band is wider in a 90 degree v8 than you would see in an inline engine because the load is angled and coming from both sides, but I've never seen the load climb the sides then change directions. If the band is tapered, gets narrow at either the front or the back, that is a sign of uneven loading. If it's a con rod, likely culprit is a bent rod. Very unusual to have it happen on a main brg but if it did I would first suspect a bent crank. Main bearing bores don't go out of alignment that easily.

An interesting exception was aluminum Cadillac engines, the pushrod engines prior to the Northstar. Notorious for crankshaft problems, specifically worn mains. There you would see tapered wear patterns and it is alleged that it was caused by twisting of the aluminum block. I suspect that was the case because the next gen engine, the Northstar, has a split crankcase like a snowmobile engine (or an LT5). An extremely rigid design.

Steve g

 

Goodness, Steve - this isn't a pissing match...you're simply incorrect

I've done over 300 GEN I SBC overhauls, not including all the weird stuff along the way.

This is where the discussion gets interesting, as it appears some folks don't understand how a bearing works. The load in a bearing of this type is distributed around the bearing bore by the oil film. Just for fun, I Googled some pics - and I'll go out and dig in my scrap bin tomorrow for some pics myself. The links are included with the pics - please point out the band you refer to in any of these.

http://restorecarsfast.com/enginerebuild/



http://www.pro-touring.com/showthrea...I-gotta-fix-it (Boy...and those upper shells sure don't look "reuseable" to me...)



http://www.chevelles.com/forums/showthread.php?t=261918 This one's a bit interesting in that the clearances were clearly far too tight...yet I still don't see a "band".



And here's a Ferd just for fun
http://www.autotraderclassics.com/ca...ld-81413.xhtml





I guess this could go on and on - but the OP has what they need to make a good decision

 

No, the problem is that some people here do know how a bearing and oil film works. How do you know how much wear is on them? You miked the pic?

Instead of showing us pictures of old brgs, explain the physics to us, you know how the downward load bounces off the oil film and in it's shattered state spreads out in a uniform circular pattern because of the crush of the shell.

Just curious, out of 300, did any of them turn out?

Steve g

 

Here you go.
http://www.hadmac.com/technical_info.htm

Note the pics of the distorted crankcase. Notice how the tops brgs show no appreciable wear and the bottoms are wiped out.

Pay particular attention to the instructions on how to tell. Progressive wear results in tapered wear pattern front to back.

Also states wear to be 2/3's of the shell. They only show the lower, assuming you are bright enough to know that's what you're supposed to be looking at.

Steve g

Edit,
Refers to diesel engine, but illustrations are the same as you see in every text book and every case of similar failures that I have ever seen, regardless of make, model. There is nothing in an old sb that makes it any different than anything else out there.

 

Gosh, Steve - I wrote a long post and then just edited it all out. But please don't put ideas out of thin air into my posts and try to pass off as mine - I'm quite clear on what crush is - and what an oil film is in a radial bearing.

The post you made with the bearing guide is pretty funny - there's no "band" of wear but as noted the wear is evenly spread across the bearing with a lessening at the parting line - exactly what I said. This isn't due to the "downward" pressure of the crank - it's simply that the bearing is thinner there. Any 35 year Journeyman has a bearing mic - go measure one Or, better yet - actually take a look at some real bearings that have been removed

The purpose of the bearing crush diagram you posted is to be clear on the importance of sizing and roundness of the bearing bore to ensure the bearing is round when installed - and ensures a consistent clearance all the way around the bearing. This is where the oil film lives - and oil is only so compressable. The crank rides in this oil film - not on the bearing.

 

The 'open' forum concept is there to allow folks to contribute what they 'know' or what that 'believe'. It is then up to the OP to decide what is best for him/her after digesting all the posted information.

IMO, the open forum concept is NOT there for disagreeing (or disagreeable) folks to take exception or 'pot shots' at other posters. {which does happen on regular occasion} If someone wants to present opposing information, data....great! But, for just blasting someone else because it doesn't agree with their thinking.....NOT!!!

I say, folks should present their position in their post and be done with it. Internet arguing or taking issue with a specific poster is in very bad taste.

 

Crush built into the bearing? If the proper bearing bore ID isn't established, proper bearing crush won't be achieved. Sadly happens all the time with poor machine work.

If the bore ID is too small, the bearing will ovate and the top and bottom will press inward reducing clearance at the top and bottom of the bearing while increasing clearance and often disturbing the oild film at the parting line - all of which gives a failure indication as the OP noted. If the bore ID is too large, then the bearing presses in at the parting line - which is usually immediately fatal.

I think that perhaps all that time as a line mechanic didn't expose you to the high performance world where there are issues that arise from poor or improper machine work. This isn't to disparage that experience, but the high performance world is different - quite different - and requires development of new skills.

Steve, it is possible to disagree without being disagreeable. I try hard to take that approach, but there are always those where open, personal, combat seems to be the default mode. And those birds of a feather tend to flock together. It's a disturbing trend, and I agree there's a growing list of them.