Amici-
Thank you for the enquiries - briefly, we suffered a major failure on a new
steel crank after only 4 hrs track time, several years ago, and decided that
something needed done.
After some research, we found that there is a problematic 3rd harmonic
torsional vibration on pretty much any inline 6-cylinder motor. The 6-cylinder
Triumph motor is especially susceptible since the crank has hardly any overlap
on the journals, hence is "floppy", for want of a better term. At 7200 rpm,
the crank is twisting itself into a frenzy; the original elastomer damper
cannot cope with the forces, so something has to give way. The first victim is
the flywheel, normally as a result of an early downshift, leading to failure
of the flywheel fasteners. So we go 8 bolts, dowels & so on. The flywheel then
stays on. Then the rotor arm fails. Then the cam drive falls to bits in
various ways - cam sprocket drops off with the snout of the cam, or, in
extremis, the chain breaks - seen it , it's true!. The tensioner smashes, and
even valve springs start to fail. I've seen one motor where the engine
backplate decided to part company with the engine.
OK - it's ad break time - my kit allows either original or billet cranks to
rev through the critical rev point without risk of destruction. It's easy to
fit, but the motor needs to go backward in the frame by around 10mm, and
there's some adjustment of pulley offsets to do. If you're unlucky, you got a
long drive shaft, which'll need shortening by a bit. Most are OK. Kit costs
#525 - I will be able to reduce this to FOT if we get a few orders. Steel
crank = $3000 minimum - I think it's worth it, due to lack of collateral
damage...
Final puff- the TR-6 I drove at Mid-Ohio, which set fastest lap of the week
(with a fat rusty old tub behind the wheel), has a standard, unlightened crank
in it, wearing said kit. The telltale said 7*00..
Please e-mail or whatever - I already posted the flywheel bolt specs & so on
a while back.
Roll on VIR!!
Jon Wood
|