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Main Bearings

2K views 6 replies 4 participants last post by  94MSP9C1 
#1 ·
Earlier this year I changed the rod bearings in my motor(92k miles). The bearings did show some wear, but were probably serviceable. What was worrying me was that my oil pressure was way too low at idle and at high RPM, so that is why I changed the rod bearings and the pump.

Now move 100 miles after the bearing change. The pressure at idle was 28~30psi and while at higher RPMs 55~60psi.
So I figured lets go do a shake down run before nationals. I made three autocross runs without any incident. At the end of my fourth run, the oil pressure was zero. I immediately shut down the motor.

I pulled the motor and examined the rod bearings. All were fine except having some embedded particles.
Then I opened the mains. The three center mains spun. A significant amount of damage to the crank and burned oil on the bearings. The groove that is normally in the bearings was filled with "welded" metal. The oil filter was full of metal shavings. Mot just small glitter, but long slices of bearing material.

What causes this to happen? The rods get oil last, so why just the mains?






The bearing in this next photo is one of the rod bearings i.e. the bearing that is not black to the left.
 
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#3 ·
I was thinking lack of oil, but why did the rod bearings survive when the rod bearings are the last in line to get oil.

Is it a possibility that the mains were already damaged when I changed the rod bearings and it was just time?

The front and rear main looked just fine with minimal wear. The rod bearings just had embedded particles and did not look burned.

The new motor is being built by Ellwein Engines. I am going to get the upgraded oil pan from Stefs.
 
#6 ·
I did not touch any of the mains when I changed the rod bearings. I changed the rod bearings with the motor in the car.

I only checked the mains after I had no oil pressure and pulled the motor.

I did have the stock windage tray installed.
 
#7 ·
I did not touch any of the mains when I changed the rod bearings. I changed the rod bearings with the motor in the car.

I only checked the mains after I had no oil pressure and pulled the motor.
Well there is your answer! How you thought you could change bad rod bearings and not even check the mains is a costly mistake that you surely will never make again. Once metal gets in the bearings it gets in them all. Would not be surprised to hear that you most likely will find metal in your cam bearings as well.

Mike--94MSP9C1
 
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