TeriAnn,
you are right. Dampers needs to be designed for purpose and not use because
it fits.
A wrong damper can make it worse and rise the swing at worst case.
Chris
-----Urspr|ngliche Nachricht-----
Von: fot-bounces@autox.team.net [mailto:fot-bounces@autox.team.net] Im
Auftrag von TeriAnn J. Wakeman
Gesendet: Freitag, 6. Dezember 2013 18:53
An: fot@autox.team.net
Betreff: Re: [Fot] aftermarket crank dampeners and pullies for TR4's
On 12/6/13, 7:54 AM, John Hasty wrote:
> For what it is worth, we got 10 race weekends on our last rebuild
> running a damper from BFE. The crank broke between # 1 rod and front
> main on last race, last lap, last turn while running 1st. in EP. I
> regularly turned 6500 in 2nd, 3rd, 4th and 6200 in OD. The motor
> always ran smooth with no vibration I could feel even with the front
> engine plate bolted directly to the frame.
>
There is a nasty harmonic a little over 6000 RPM that affects the crank
towards the middle. It is probably the one that took out your crank.
The commonly sold harmonic dampener was picked to tame the harmonic at
around 5200 RPM that tends to break the crank at the flywheel mounting
flange. Which is why the stock engine is red lined at 5000 RPM and a number
of people have added harmonic dampeners to rev higher.
The story I once heard was that some folks had access to British Leland's
crank test sheets that included harmonic testing. They compared other
cranks to the TR3/4 crank to find one with the closest harmonic match. They
choose the harmonic dampener for that crank to use on TR crank to tame the
5200 RPM harmonic. The harmonic dampener that is commonly sold for the
TR3/4 crank was specifically chosen because it had the correct
characteristics to tame that harmonic.
That leaves me wondering if the other harmonic dampeners have been harmonic
tested with the stock TR crank to see what it does to the harmonics? I'm
assuming that different weight and diameter dampeners affect harmonics
differently. Just wondering
TeriAnn
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