BALANCING YOUR BIKE MOTOR
by: DIYMark MBc Member (MotoredBikes.com: Motorized Bicycle Forum - Powered by vBulletin
edited by: JW
1) First decide on your balance percentage. The recommended is 55%.
2) Now you will need to weigh the total piston assembly - piston, rings, gudgeon pin, and record it.
3) Now weight each end of the rod with the corresponding bearing inserted into its race. Weight each end with the rod in a horizontal position. 2 accurate scales are ideal, but using one will work too and record it.
4) Add the piston assembly weight to the little end weight and times his amount by the balance percentage (keep in mined 55% equals 0.55) then add the big end weight to this number and you have balance mass.
BalanceMass = [( PistonAssym + RodLittleEnd) X 0.55 ] + RodBigEnd
5) Now make up a BalanceMass that weighs exactly as calculated above. You can make it from anything
such as nuts/bolts taped together or be fancy and machine a collar.
6) Inspect and re-machine the crankshaft counterbalances, if required, to obtain concentric components.
7) Fix the BalanceMass to the crank pin, press together, true, and mount your crank on 2 knife edge bearings that are level to the ground and parallel (2 steel rods will work).
8) You have to remove enough metal from the crank throws symmetrically (left/right) so that with the balance mass attached to the crank pin, you can turn the crank along the knife edges and no-matter what position you leave it at, it won't roll over to the heavier side. If the BalanceMass itself is too heavy, it will require removing an amount of metal from the BalanceMass and then removing amount/0.55 from the piston assembly. This requires careful thought. Although not necessary, if you want to be precise, use the density of steel/aluminum to calculate possible diameter holes and their depth to equal the desired weight to be drilled.
9) Once you are satisfied with the balance, dissemble the crank, clean and oil all components, press together, and true the crankshaft.
Although you cannot balance a single cylinder, this might get you a little closer so it doesn't give yer mits "lawnmower" effect at 8500 RPM. I'll give it a shot soon.
Oh, yea, please make corrections or give feedback so others can use this or other balancing techniques to balance their motors. It might be a good idea to keep it at the "shade tree mechanic" level (because I'm one), to make it possible. If you can get a good balance, share the tech info with us as to where to drill holes, what epoxy you filled the holes with and so-on.
