LB7: Main bearing damage

[dirtydmax]

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...

sound like I have the same situation.always had a vibration but always at idle.ran rough until boost came up then it was game on.It made enough power to break the dualls loose at hwy speed. An af cam is going in the new build no q, s asked.

 

[dirtydmax]

I pulled the Pistons and the rod bearings are perfect so I'm leaning towards the block being distorted,that would explain both builds with the same bearing failure.new block and crank headed to the machine shop because I don't think this prob will be easily fixed.Could high cylinder pressure cause this damage or does it look like a misalignment issue?

 

[S Phinney]

I pulled the Pistons and the rod bearings are perfect so I'm leaning towards the block being distorted,that would explain both builds with the same bearing failure.new block and crank headed to the machine shop because I don't think this prob will be easily fixed.Could high cylinder pressure cause this damage or does it look like a misalignment issue?

If the rods bearings look good then it is not cylinder pressure.

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