Hi Group, I am doing the M20 500cc to M21 600cc conversion on my WD M20. Can anyone advise a reasonable Balance Factor for the M21 F/wheel, Rod, Piston etc assembly before I have to split the wheels to weigh the big end assembly? Greg
You shouldn't really need to do anything to it, just assemble it and true it. The closer you can get it to zero run out the better and smoother it will be
I think Ian covered this before If my memory serves me right (without searching the forum) it is 60% please Ian correct me if I'm wrong! If you are using a standard M21 piston (or equivalent)you don't need to do anything as the M21 flywheels already have this balance factor built in
The piston weights should be nearly identical for the M20 and M21 , the only difference is that the gudgeon pin is set lower in the piston, so there may be just a little difference in the 2 pistons because of the extra metal involved in bracing the pin a little lower down
Standard balance factor is 58%...I generally use a 60% figure. If the difference in weight between a standard piston assembly and your new one exceeds 1 1/2 ozs. you should rebalance the crank assembly.
Normal production tolerances used when the cranks were made can vary and I have found some engines can be improved by rebalancing even with standard components...it's really down to how far you want to go...Ian