Quote:
Originally Posted by Ken MA
Trying to track down a thumping noise on this motor accelerating under load.
Motor was rebuilt 2 years ago and driven 2000 miles.Pulled the pan and made some measurements
Reground Crank .020
Rebored with new pistons .060
Re-babbited mains .0015-.002
new babbit rods .002
Crank end play .009
There is a lot of side to side wear on the rod bearings .010-.024 between the thrust end of the rod bearing and the crank . Thrust surface on rear facing #2 bearing is worn thin. What is an acceptable end play clearance on rods? Is #2 pounding against the crankshaft causing the noise, or is the .009 crank end play causing the problem? Before this block was rebuilt most of the babbit on the original rods was worn away . Any ideas on the cause or fixes is appreciated!
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.009 end play is wore out. We set from .003 to .003-50, on the rear main.
The center main should have About the same amount of clearance, on either side of the crank, when the crank is set.
Pictures would help!
Rods have to be checked for Twist, Bend, and Offset, and most builders don't, thinking their rod machine, or mill will bore them straight, or they are using wore out machinery. The same goes for the Rod alignment machines, either wore, or the cast has moved, as in Wilson Rod Aligners. The babbitt should close to equal, on both sides. But still the most important thing, is Alignment.
The side play in a Model A Rod should not be over .012 thousandths, Never under .003. We set the clearance at .005 or .006. Some cranks when reground, the standard has been opened up, on the width.
Herm.