Dear Bill-
We're looking at it. The problem is that the damper needs to go ahead of
the crank pulley on the 4-cyls, leading to clearance issues. I hope to have
something sorted out by Christmas - it's just finding the time, and of
course considering the differences between TR-2, TR-4, and TR-4A. It would
probably knock out the ugly thrash throughout the trans at around 4600-4800
rpm with an unsprung clutch plate, which must be wasting power & doing
nothing for the longevity of the trans. I'll post with developments.
----- Original Message -----
From: "Bill Babcock" <BillB@bnj.com>
To: "'A.J.Wood'" <wood@dandrade.freeserve.co.uk>; "friends of triumph"
<fot@autox.team.net>
Cc: <kaskas@cox.net>
Sent: Friday, September 26, 2003 4:59 AM
Subject: RE: 6-Cylinder crank damper
> So did you figure anything similar out for the 4 cylinder cars?
>
> -----Original Message-----
> From: A.J.Wood [mailto:wood@dandrade.freeserve.co.uk]
> Sent: Thursday, September 25, 2003 4:24 PM
> To: friends of triumph
> Cc: kaskas@cox.net
> Subject: 6-Cylinder crank damper
>
>
> 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
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