VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Lapping sticks and polishing grits.

I have had cranks polished at a machine shop.They use a leather strap and th journals look like chrome when they are done.

Johnny,600 sounds a little coarse for polishing.I think tha t I would start with 1000 and finish with crocus cloth.If you are using shimmed rods the good thing is that you can adjust to fit.Either way you really can't take that much off.On the ones that I had polished on was a new crank that had a bit of surface rust and the other was well used but not worn and just wanted to be good to it. both worked out well.

I'm NOT an expert on cranks, but I use 1000 to 1200 and up to wet sand paint, which can be repaired if I screw up. Since the crank is harder to repair, I think I would start too conservative. You can always take more off, its really hard to put it back on. IMHO :eek: :eek:

I grind Cranks for a living so I figured I'd put my 2 cents in. What I use is 320 grit BUT before it touches a crank I put an old grinding stone to it to take all roughness off of it. In others word its almost worn out before I use it. I use that to take surface rust or small imperfections then I use a scotch brite belt that removes no material at all( the scotchbrite belt is all I use on a freshly ground crank) but leaves an extremely smooth surface on the crank. Another trick you can use if say someone nicked it with a rod bolt or something like that is to use a small file , like a points file to take the high spot down then polish. The easiest way to ruin a perfectly good crank is to polish it too much. If you try to remove material you will make it out of round and normally it will be low in the middle , the belt will roll up on the edges.

I glad there are people like Scott, JYD, MrMack,etc who have the experience to give good advice, this is one of the great things about this site.

well a couple reasons the first is that's what the guy that taught me told me to do !! I use a new belt to remove heavy rust or bearing material that has stuck to a crank but what it does as it cuts is it makes a low spot in the middle of where the belt rides. By wearing the belt down first it remove much less material therefore you get less of a low spot. Why 320 well thats what most crank polishing belts come in. I have seen cranks that were ground then polished with a new belt that were worse that worn cranks. If you saw a crank that had been polished with a new belt ground it would scare the heck out of you. It usually takes about 5 thousandths to remove the damage.