Hey guys. let me put some input here.
First of all-any polishing or massaging on crank will not give anything at all. if you think that after polishing edges your engine went up in power-it just in our heads.
For off road engines I will sugest as follow-check and/or aler induction timing to open @ 38 ABDC and close @ 52-53 ATDC, second thing is check transfer and exhaust timings-transfer should be somewhere between 120-124 and exhaust 156-158. Never ever put piston or liner to any metall working machine as lathe or mill. To fix them secure you will need apply a lot of force and it will defenetly bent out of original geometry-then it will be paper weight. I can sugest to change anglr on transfer ports (use only dremel and your stay hand) to more steep angle, let's say originaly most of engines is about 15 degree, if you can do it to 20 will be very good result. One more thing-it will be very helpfull prepare engine before first time start-I mean piston needs to be lap in to certain size. Usualy it is head button deepnes + 1.5 mm. It will save a lot of tiem and fuel for brak in and it will make your racing life of engine about 30% longer. This thing can be done by using lapping tool and lapping compaund ( which I know it will be hard to get) or by using very fine sand paper (2000 grid) and lap piston to desired size (which will be very hard to do and don't scrw up piston). Any way if samobody will try to do that, please remmeber-first clean piston and sleeve and make sure there is no oil at all. then put piston to the sleeve and push it till stops on the top. Mesure the distance from top edge of sleeve. Ddeterminate what size you will need (mesure head button part which goes insdie sleeve ). Next step is cut piece of sand paper wide as lenght of piston, wrap ones around the piston as clamp and with slight pressure turn piston arround 2-3 times, clean it very well and put piston to sleeve again and mesure-do it till you got piston to size you want to. It sound that it is easy to screw up with sand paper, but not really. First of all I can assure you i did many many times for over 25 years I am in hobby, second is that real size will decreas just by couple of microns on diameter. It doesn't mean that it is impossible to scew up-there is great chance it might happened, but if to be very carefull, prepare yourseld very well (never be rush work on motors), try first on dead pistons.
if you have any more questions please fill free to ask and I will be happy help.
Oh one more thing-please to mean people don't start bushing my english-I am not native born american and english is my second language.
Edward