Radial crankshaft load at flywheel 2

[amorrison]

My understanding is that in automobile engines the back crankshaft bearing will only last "minutes" if the engine power is "taken off" by a chain or belt due to radial forces.

The only engines that have bearings designed for radial loads seen to be snowmobile engines with CVTs.

Can these bearings be "upgraded" or are there other solutions?

Thanks

 

[patprimmer]

Tmoose

A very good point. Typically on V8s Supercharger drives pull directly against the oil hole as the supercharger is normally mounted over the valley.

Most after market high performance V8 top main bearing shells have an oil grove to distribute the oil feed over 180 deg and this would overcome that problem in that case. It is to long since I looked at an OEM bearing shell to remember.

Regards

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[Tmoose]

I think lots of top main shells are often grooved, stock. With a single feed oil to the rod journal that would provide rod oil approximately when it was at BDC +/- 90 degrees. On a generic 4 stroke On the power stroke the "bottom" of the rod oil clearance would be open. On the exhaust stroke decelerating the piston the "bottom" would also be open.

On cranks from badly maintained engines the rod journal wear is primarily on the "underside" of the journal, which is where the rod would be pushing at BDC. My theory is the hydrodynamic oil film starts pretty thick around 90 degrees BTDC when the oil is new and cool, but the film getting thinner and thinner as oil is squeezed out, (and sheared oil warming and getting squeezed out even more)until the oil film is thinner than the abrasive chunks, and if the oil level is too low, then the contact becomes metal to metal, taking the inserts down into the copper without really failing.