spun bearing on $500 '48 cub

Mon Jun 28, 2004 8:57 am

Okay, guys I took your advice and picked up the $500 dollar cub. Got it on Friday and drove it off the rollback into the barn. Serial number shows it is a 1948. I removed plug wires till I isolated the knock to the back cylinder. I pulled the oil pan. In the pan was some old gasket material. There was one or two minute pieces of backing from a bearing. I removed the number four rod cap, closest to rear wheels. The bearing had spun. To visual and finger inspection the journal appears smooth. I mic'd it with calipers this morning at around 4 am in the dark. From what I could tell I was getting a measurement between 1.485 and 1.490 at several points. So I am thinking maybe some .010 bearings and some light journal buffing with a piece of emery cloth? I am thinking the failure may have been due to the gasket material in the oil pan. I haven't checked the timing or to see if there is any crossfire on cylinders yet. What is the best way to check the rod for concentricity? Do I need to remove the piston and bolt the cap up, or do I measure the cap and the rod end seperately? Is it possible that the spun bearing removed material from the cap and rod, which would warrant a higher udnersize or is the rod and cap material harder than the backside of the bearing?

Mon Jun 28, 2004 11:17 am

Crank rod journals should be 1.498 - 1.499 inches.
It would be best to take the crank and rods to a machine shop and have them checked.
The rod should be checked with the cap on and tightened to spec.
Usually their will be some visual damage to the rod or crank, the bearing material is much softer than the crank and rod.
You do need to make sure they are not out of round from being hammered.