Im not trying to start a flame war here, so please dont take it that way.



Isnt the purpose behind the counterweights to offset the weight of the rotors on the lobes of the eccentric shaft? I see a potentialy damaging setup. Especially in an old school 13b their the rotors originally weigh at least one lb more than the FC rotors each.

 

so far if you get 2 rotors let say 86na i should them get the front counter weight as well and flyweel.

 

Put it this way, if im wrong, what did it hurt by using the right counterweight and flywheel. But if im right...

 

From a reality standpoint, you probably wouldnt notice the slight increase in vibration with using mismatched rotors and counterweights. I drove one engine for 20K miles that was a S4 block, but S5 counterweights. Never noticed a problem, until I tore the motor down. The main bearings were worn oblong. They were within spec at one part, but were about .010 out of spec 90 degrees from the first spot. The top and bottom on the bearings were worn down.



From a physics standpoint, the counterweights are there SPECIFICALLY to counteract the imbalance of the rotors relative to the shaft. Remember how the rotor lobes on the ecc are not centered(hence eccentric shaft)? The rotors were about 8 oz diffreent between S4 and S5, while the counterweights are different by about 2 ounces.



Yes its important to have matched rotors and counterweights, but it will not grenade an engine(unless you mismatch the rotors). It will, though, lead to greatly accelerated main bearing wear, and undoubtedly extra stresses on the motor.