Crankshaft Drag Desired after Engine Rebuild

Posted by Gordon Biggar on March 04, 1998 at 00:18:32

I've been doing this engine rebuild "by the book" (Les Andrews' book, in this case). Les calls for a drag of 35 foot pounds or less on the turning of the crank when the engine has been rebuilt.I'm coming up with 58 foot pounds.

The Model "A" block was re-sleeved, and standard pistons and rings employed.Using Plastigage, all of the main bearing clearances were set at approximately .0015 inches, based on 50 foot pounds of torque (final torque setting was 80 ft. lbs.).After all three main bearing caps were installed, there was not too much drag on the crank (probably 15 foot pounds or so).

Naturally, with each piston and rod added, the drag began to increase.The rod bearing clearances were also set to .0015 inches at 35 foot pounds of torque.Although the pistons appear snug in their sleeves -- as they should -- each one has .009 inches of clearance between the piston and sleeve, measured at the top of the block.(There is no lateral movement of the pistons within their respective sleeves -- at all.)

Is 58 foot pounds of drag too much?Where have I gone wrong?Where did Les obtain his 35 foot-pound figure?Do I go back and increase rod bearing clearances to .002 inches, which would be outside of specifications?

It's a great learning process, but oftentimes frustrating!Thanks for any advice that one may have on the subject.

Gordon Biggar
Houston, Texas


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