V-Twin Flywheels
V-Twin Flywheels
(OP)
On V-twins with built up cranks, like Harley, the flywheels, crankpin and output shafts are assembled.Then the assembly is put into a fixture to check for flywheel run out (side to side). If runout is not in spec, you take a lead hammer and whack the flywheels until it is.This has always bothered me.It seems that if you can make the assembly run true with a few whacks of a lead hammer, then it could be easily un-done by the normal operational forces of the engine. What do you guys think?





RE: V-Twin Flywheels
RE: V-Twin Flywheels
Crank welding had best be done by experienced people who are well aware of the problems that welding can create with typical crank steels.
RE: V-Twin Flywheels
Stock Pre evolution HD flywheels were cast iron with mainshafts and crankpin retained with nuts pulling the shafts' deep into fitted tapered joints. Early PH (power side) mainshafts had a drive key too, but that is no defense agaist a loose creeping taper. In the 80s they went to much more secure BIG taper, BIG nut torque, and no key. The crankpin has a small key, but on the RH side to align an oiling hole, not to share some kind of load. At some point The racig XRs had integral mainshafts and flywheels.
Some Japanese multis use crank "flywheels" forged of steel with integral mainshafts.
Drag racers, and VERY abusive street riders could tweak/shock the multi cranks out-of-true with aggressive starts with sticky tires, unless the pressfitted joints are welded at the ends. HD big twin drag racers sometimes brazed the left hand output shaft to the forged steel S&S flywheels.
RE: V-Twin Flywheels
RE: V-Twin Flywheels
Cheers
Greg Locock
RE: V-Twin Flywheels
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: V-Twin Flywheels
I don't think a tilted, but centred, disc has any particular forces on it that are harmful... do you? I can see that the non-existent centrifugal force will tend to straighten it back up, but that's about it.
Cheers
Greg Locock
RE: V-Twin Flywheels
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: V-Twin Flywheels
RE: V-Twin Flywheels
But I still don't see many significant forces trying to knock the thing out of true in the first place.
The only one I can think of is gyroscopic precession due to cornering.
Cheers
Greg Locock
RE: V-Twin Flywheels
Those bending forces in the crank are the reason why a shaft which is statically balanced may not be dynamically balanced. The bending forces rotate with the crank.
Jeff