[TR] TR4A crankshaft extension

[Randall]

---- john-marie at sbcglobal.net wrote: 
> In my
> pedestrian mind, seems like less mass in front of the pulley is better. 

As I understand it, the issue is that the crankshaft has a resonant frequency (actually several of them), much like a bell does.  At just the right rpm, the pulses from the cylinder firings match the resonant frequency and cause the crankshaft to "ring" and twist/flex farther than it would normally.  Keep that up for long enough, and the metal fatigues and breaks.

The damper works much like holding your hand on a bell, and eliminates the ringing.  If someone had been touching the Liberty bell, it might not have broken <g>

That said, I've covered over 200,000 miles without a fan or damper; and never broken a crankshaft.  I have seen broken crankshafts, but always in racing motors that made considerably more than the stock 100 bhp and turned more than 5000 rpm.  Perhaps it's more of an additive problem.  Or maybe I've just never run for long enough at a "problem" rpm.  I've heard it said that the first problem is around 5200 rpm, and I don't drive up there very much :)

Randall