LB7: Main bearing damage

[dirtydmax]

Motor is out for some upgrades and was really curious how the mains held up after a summer of abuse.This motor was bought last winter with the understending it needed bearings and an oil pump but discovered it had 3 spun center mains,The crank,cam were damaged to badly to salvage but we managed to save the block after new caps,Main bore,crank and cam.I pulled the caps and was suprised to find almost the same damage on the center mains.Im starting to think there is something really wrong with this block but I thought I'd get some opinions.

 

[PureHybrid]

Was it a good shop that line honed it?

 

[dirtydmax]

Was it a good shop that line honed it?

Very well known shop did the mains and installed the crank with h bearings.makes no sense the same 3 are damaged for s second time after 2500 kms.Not gona lie...I was not easy on this motor with many 100 psi pulls.

 

[S Phinney]

There is a problem. They did the assembling as well? What clearances were used?

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[DewDewMax]

X2 what were the main clearances? Shitty to hear man! Definately something going on there!

 

[Chevy1925]

Ouch! That is not pretty

 

[malibu795]

Shit the mains from breaking my crankshaft looked better then that!!
What did the top size of center 3 mains look like?

 

[dirtydmax]

Shit the mains from breaking my crankshaft looked better then that!!
What did the top size of center 3 mains look like?

Top bearings have normal wear on the 3 centers.Im not sure on clearance.once the crank was installed I didin't check.

 

[onebaddmaxxx]

Top bearings have normal wear on the 3 centers.Im not sure on clearance.once the crank was installed I didin't check.

So you installed without checking clearances? Eek

 

[dirtydmax]

So you installed without checking clearances? Eek

Machine shop installed the crank after a main bore.saw no need to check as they are a reputable shop.The question is why the 3 center bottom bearings are fukerd but the tops are ok?

 

[ikeG]

We just dealt with this on our old motor that we sold. I know Broviak has been dealing with this this summer, he may have found a fix. Talk to him.

 

[PureHybrid]

Very well known shop did the mains and installed the crank with h bearings.makes no sense the same 3 are damaged for s second time after 2500 kms.Not gona lie...I was not easy on this motor with many 100 psi pulls.

Even the two good ones look like there was some contamination. If running that much power/boost is trashing mains, your upper rod bearings should be shot also. The reason I ask is because usually when only the center ones are toast, something isn't lined up or straight. Whether it be the block or the crank.

Call me crazy, but I wouldn't let a machine shop build my motor unless there was a warranty.

 

[dirtydmax]

We just dealt with this on our old motor that we sold. I know Broviak has been dealing with this this summer, he may have found a fix. Talk to him.

I give him a call tonight.thanks

 

[Fingers]

Oil. That is, lack of it.

 

[duramaxzak]

Out of curiosity, what oil were you using?

 

[dirtydmax]

Out of curiosity, what oil were you using?

Rotella 15 40.always had great oil pressure.

 

[S Phinney]

Check the upper rod bearings to see how they look. If they look good then you definitely have a bore issue. If they look terrible as well then you have a tuning issue with to much timing. Those are the surface areas that carry the load from cylinder pressure.

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[dirtydmax]

Check the upper rod bearings to see how they look. If they look good then you definitely have a bore issue. If they look terrible as well then you have a tuning issue with to much timing. Those are the surface areas that carry the load from cylinder pressure.

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Could the block be flexing or distorting that much to be taking the bearings out?The 3 bottom bearings were also squished inward.The damage on 1 and 5 I think we're from the bearing material from 2-4.Thought I'd ask those with more experience than I. Starting the new build with a fresh stock bore block so will looking for a set of used slugs if anyone has some.

 

[S Phinney]

That is not likely. Either the alignment of the bore is off and/ or they were too tight.

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[Yellow Jacket]

Or crank deflection under load, pushes the oil off to the sides and top... Good oil and oil pressure and proper clearance allows the crank to float while rotating... Along with a good line bore.

First Duramax I built for myself, wiped out the center 3 bearings the most (copper showing) and crank failed mag check... That engine also vibrated the most at certain rpm ranges, but was much smoother at idle than any stock Dmax I've been around. It was factory (externally) balanced and normal firing order, in the last season of use, we could see hot oil temp (coming off track) oil pressure starting to drop over time. Had ~13,000 street miles and 60+ hooks with s366/s480 twins, and 40+ hooks in ODL truck the first season.

Went internally balanced next go round, and kept same clearances and same timing, bigger injectors with less duration... Made it 2 more seasons ODL, balancer was wobbling after Scheid 2nd hook that year. All bearings looked better than prior engine, literally just a few scuffs in #2 main from crank wobbling...

So went with Altered Firing order camshaft same clearances, more timing, and more fuel... And bearings have been beautiful ever since...