It is common practice to resurface badly worn irons by lapping. Less than .003" is often the ideal. More requires that gas nitriding be redone to restore hardness to the wear surface. Very early irons were not so hardened, and would show wear in less than 100,000 miles.

 

While grinding can also be done, similar to grinding a cylinder head flat, generally more than.003" would be removed. Then you would lap to get a good looking sealing surface, then re-nitride the irons.

 

When the grinding is done several times as would be more likely on ported racing irons of high value, the engine gets to be a bit shorter with each such event. In some cases, the shorter engine would have the rear main bearing ride up onto the radius on the rear main bearing journal. The cure is easy enough. Just make a gasket of card board (beer carton) that has the same pattern as the flange on the rear stationary gear. If one gasket is not enough thickness, then add a similar gasket under the front stationary gear. In the first case the offending bearing is moved to the rear the thickness of the gasket. In the second case the crank is being moved foward the thickness of the gasket.

 

Since only the wear surface is machined, it would not affect the pump land area or the stationary gear installation depth. I have in some rare casses had to shorten the rear stationary gear even though I was using new irons to build an engine. Last year in fact, on a showroom stock 12A. I was having trouble getting the thrust clearance right (.003") and found that if I loosened the rear gear bolts it was fine, but vanished with the bolts tight. The gear was too long. I cut off .040" on the lathe, and all was well.

 

Another thought on the oil pressure.

 

Some folks remove the balls and springs under the oil squirter jets in the crank. This is done in racers, and the idea is that when you jack up the oil pressure to 100 or 115 PSI, then the stock jets are too big (about .200MM) and a Weber main jet is installed in the bottom of the stock jet holder. I use a 180 main jet.

 

This is fine for racers that idle at 2,200 RPM. No notice of oil pressure above 80 PSI at this speed. If this is done to a street crank and stock idle speed is attempted, 5 to 10 pounds of pressure is more likely.

 

It is a good mod for shifting at 9,600 RPM or more. It is a dismal change for a street engine.

 

The picture is the layout of the thrust assembly.

 

Lynn E. Hanover