Flywheel Theory	www.virtualindian.org
		Home / Archives / Flywheel Theory 1 / 5

From: "Moen" <moen@get2net.dk>
Hi Keith; Is there really significant torsional vibration in an Indian flywheel assembly? You may well be right, but it seems quite short to me compared to car crankshafts.

From: Keith <Packardv8@aol.com>
It's relative; Mostly to strength of material than to length. NOTE, that HD in certain big inch engines used a wide heavier flywheel on the rite side and a skinnier lighter wheel on the left side (primaryside).  I do not know for sure why they did that, but my guess is that they were trying to compensate for the load between the drive shaft and pinion shaft.

From: "Cotten" <Liberty@npoint.net>
Keith! According the Herbert Wagner's ' "H-D,'30-'41" history, the Davidson boys tried to head west out of St. Louis to the west coast to promote their new '30 VL's. About 500 miles later they telegraphed for help, and the factory issued an  upgrade of a big left wheel and a left case to match. The problem was a lack of torque to pull hacks, and the massive left wheel remained in big twins until Evo's.

From: Guy <guyiii@home.com>
Does the crankpin twist? Sure - a verrry little....but if it's too much the wheels will be non-axial & the bottom end will bust I don't think (merely MHO) that its a factor....Ummm, on my HD the heavy wheel was the driveside...to conteract the torsion you described....but S&S & T&O wheels are equal wt....and an old timey HD mod was using 2 right hand wheels for quicker acceleration...

From: Keith <Packardv8@aol.com>
What I am refering to is a twisting of the ENTIRE assembly, not just the crankpin.  I think we can all agree that there is a greater amount of load one the left (primary) side of the crankpin, left flywheel and drive shaft as opposed to any components on the right side. NOTE:  I stand corrected on the wide and narrow flywheel positionaing as you mentioned.  BUT, now that leads me to believe that the heavier wheel was used on the drive side most likely for strength.  But I still really dont know for sure.

From: "Rohan Bradney" <rohanb@primus.com.au>
guyiii@home.com wrote:
>the flywheels are massively more resistant to deformation than the
>shafts....effectively the wheels don't deform....even a verrrrry little..."

I dunno, people say "as solid as the ground I walk on" - until they see an earthquake....The wheels might deform less than the shafts, but only in proportion to their relative sizes. English bikes at one stage, as revs and power outputs rose, went to a better grade of iron (meehanite) because the wheels were deforming sufficiently to explode !!!  Steel cranks have been common in racing for many years, for precisely the same reason. The bit that matters is the connection between the crankpin and the drive-side output shaft, and because of the counter-balancing this is pecisely where most crankwheels are the skimpiest.
And as recently as twenty years ago engines went to "superblend" type roller bearings because the crank was flexing sufficiently to make the ends of the rollers "dig in" and destroy themselves. Superblend rollers have a slight taper on the end of the roller, so that when the crank flexes the taper bit takes the load. I think Harley some engines currently use these, and they were the salvation of the Norton performance engines of the 1970s.