Here is the thing, polishing a crank journal is what the machinist does as the last step in machining a fresh crank. The machinist drops the rotating flex belt on the journal and gives it a little touch. It’s not minutes on the polishing belt, it’s seconds. For a crank that has been sitting a bit and has a little surface rust, it’s essentially the same deal, even with the shoestring method. It’s a few cycles of the abrasive cloth. If the journal won’t clean up with a few cycles, it has to be recut.
On a crank that is in really good shape, say a standard size crank that is in near perfect shape, yes, a touch up with the polishing belt may be all that is necessary. Any more then a touch up you are changing the size of the journals and thus what you really need is a full cut and polish to the next size. Look at the photo below. That is the best crank I have ever had. A 56 235. When the machinist mic’d the crank he said it was standard and that the only thing I would do is have it polished. It got a couple of seconds on the belt and that was it. Look at the journal, it’s not perfect but it’s pretty close and it started out pretty close.
Hours of polishing? I suppose it’s possible but you would need to be polishing to a measurement certain matching each journal just to get to the right size bearing, .001, 002 and for that you need a mic and full access to the crank journal. Really what you are doing is cutting the crank using Emory paper.
If you are just looking to get this motor running, take out a crank bearing and a rod bearing shell and look on the back for the size. Order replacement bearings. Give the crank journals a quick polish with the Emory and string. If you have a mic, mic the journals and the bearings (installed) and see what your clearance is. If no mic or you don’t have the skill set to do those kinds of measurements, Put it together and use some plasticguage and see if you can discern a general clearance. If the clearance is not too great, run it. You might very well get some mileage out of it.
If you want to do a better job, have the crank cut and polished to an available bearing size, .010, .020 whatever, and put it back together and eliminate the risk of having to do the job over again.
