Crank pin "fretting"?

[David Murany]

Check the clearance between the backside of the crank and the bearing. I have had to shim the outer bearing to pull the crank back in a lot of my motors due to it running too close to the drum side of the engine.

 

[Rick Doane]

Hello Terry:

I have seen this many times. It absolutely is NOT an oil issue. It absolutely IS a misalignment issue. The rod is not running in the center of the bore. Careful measurements of the case bearing cups is required in order to place the crankshaft in the correct position and to calculate the shim thickness required. Incorrect thickness can also be a disaster. One still has to have end play in the crankshaft after assembly.

Regards....Rick

 

[Joe Warren]

Run STOCK CMB Needles the Correct Length. Not Aftermarket Needles that is too long & effect crank end play. The length of the needles Does Effect CrankShaft end play.....

 

[Terry Keeley]

Run STOCK CMB Needles the Correct Length. Not Aftermarket Needles that is too long & effect crank end play. The length of the needles Does Effect CrankShaft end play.....

They were stock needles.

 

[Tom Foley]

Might just be a bad crank . I've never seen that on any MAC or CMB crank from
45.- 91 . I have been beating my VAC .91 s like circus animals for years !

 

[Terry Keeley]

Might just be a bad crank . I've never seen that on any MAC or CMB crank from
45.- 91 . I have been beating my VAC .91 s like circus animals for years !

I think it was a worn out rod that ruined three cranks unfortunately...

 

[Wasted wages]

Terry, I find it hard to believe that as meticulous as you are with your motors, (measurements etc) .. that something like this would escape your eyes!! I still think you are dealing with a lubrication issue of some type.

After the second crank, I'm pretty sure that a bad rod would have shown up in other ways that you would have caught. No?

Scoring, burn marks, bluing, out of round, bending, thrust loading marks elsewhere in the motor...it's hard to believe that other parts associated with the damage showing up on the crank haven't been seen on themselves... like the needles, rod big end issues etc...

 

[Terry Keeley]

Terry, I find it hard to believe that as meticulous as you are with your motors, (measurements etc) .. that something like this would escape your eyes!! I still think you are dealing with a lubrication issue of some type.

After the second crank, I'm pretty sure that a bad rod would have shown up in other ways that you would have caught. No?

Scoring, burn marks, bluing, out of round, bending, thrust loading marks elsewhere in the motor...it's hard to believe that other parts associated with the damage showing up on the crank haven't been seen on themselves... like the needles, rod big end issues etc...

Ya, it was a sneaky one, as mentioned when it went together it felt good because the side of the rod closest the crank was only worn 0.001" in diameter (5 tenths/side) but with the other side worn 0.0025" I think the needles were allowed to skew at that end causing the brinelling on the crank pin.

When I mic'd the needles in the middle they were good, I should check them near the end that was at the rotor side.

 

[Wasted wages]

And the needles show no flat spotting or metal transfer at all ? Or marks in the big end bore ?

Weird.