Boxerworks.com

Hoping for help...

1978 R80/7 ~30k miles. oil clearance spoec is .0007"


Main bearings were replaced they were RED. Crank is w/in wear specifications. New RED bearings were installed. the oil clearance for the new bearings works out to .0001" to .0002"; the factory specs is .0007"

Checked the old bearings [after they were pulled] the oil clearance worked out to .0004" to .0006".

Obviously, the old bearings had too little clearance.

How do you fix the too small oil clearance?

Hard problem, something must be squirrely in crank to block alignment/fit. Probably only real solution would be to line bore the block, next size over.

buffalotankbob wrote:
How do you fix the too small oil clearance?

Run it without any oil.

Are the two measuring instruments calibrated Bob? Could the discrepancy lie there?

"Run it without any oil. "

Um.... That's how I got my new bearings....

-not.

What I read is you ran without oil...or not enough. Then replaced the bearings.
BUT the old bearings were tighter than the OEM spec allowed anyhow.
I assume you can see the wear on them...and the crank is OK.
SO, either the old bearings weren't REALLY trash, OR how you are measuring them is giving the wrong numbers, OR they are not seated as tightly in the case as they are expected to be.

You are using "Plastigage" or similar stuff to measure the clearance, I trust? (Only possible on the rod big-ends, tho)
My OLD manual specs clearance on the mains and crank journals as 0.029mm to 0.091mm (0.0011 to 0.0036 inches)
Rod big-end specs from the same book are 0.023 to 0.069mm (0.0009 to 0.0027 inches)

There are some errors in many of the manuals.