You need a shop manual that gives the specifications for the engine. Compare those to yours. .010" .020" .030" is standard over sized bearings. Most crank grinders will not go over .020". The bearing surface is hardened to take the wear and tear of engine life. Its only so deep in the material and when you go to grinding .030" (.015" per side) off, you risk the chance of getting into softer metal. This measurement, .010" is ten thousands of a inch smaller then what the crank started out as. It was ground down smaller to remove damage. So with a small crank journal, you need bigger bearings to take up the space. Rods journals are the same way. The rod itself can be repaired. The cap is ground off slightly to make the hole oblong, then the rod and cap are bolted back together and honed out back round to the correct size. You can use standard bearings on a repaired rod if the crank is standard size. Go to a online shop manual!
A spun bearing is just what it sounds like. The two tangs that hold it in place in the rod have failed. Most likely the bearing surface of the crank went bad or oil supply was lost to that one journal and the bearing seized to the crank for a moment. When this happens the bearing tangs won't hold and the bearings rotate in the rod. Once they get loose, the problems compound very quickly, till you get where you are now. The rotating and pounding destroy the bearing halves, the rod, and usually the crank. On top of that, all the metal from the bearing is now dispersed in the whole engine. I would bet money, all the bearings are impregnated with bits of metal.
Main bearing measurements can only be done with the caps torqued in place. The outside dimension doesn't mean much, you need to measure where the crank rides while torqued down with proper shims if applicable. You also need to measure in a couple of spots, usually north/south and east/west to get a good ideal of true size.
Joe
Last edited by Joe H; 04/11/2013 11:25 AM.
