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.
-----Original Message-----
From: fot-bounces@autox.team.net [mailto:fot-bounces@autox.team.net] On
Behalf Of Michael Porter
Sent: Thursday, December 05, 2013 8:35 PM
To: Randall
Cc: fot@autox.team.net
Subject: Re: [Fot] aftermarket crank dampeners and pullies for TR4's
On 12/5/2013 4:54 PM, Randall wrote:
> ---- toodamnfunky@comcast.net wrote:
>> I second that. If a harmonic balancer isn't needed on the tr4 then
>> why have it?
> The problem is how do you define "needed" ? I've seen the broken
> crankshafts, they do happen. And although the breaks are sudden of
> course, I believe the damage happens over a long time, likely only
> when running at one particular (resonant) rpm. If running a dampener
> (it's not really a balancer since the TRactor motor is already
> balanced without it) will lower the chances of a DNF and lost weekend
> from a broken crank, maybe it's worth sacrificing .01 second off your
> lap time. (Or shaving that much more weight off the flywheel.)
>
Mostly in agreement with Randall on this one. I'm going deep into memory
(so, I may surface with sludge all over me), but weren't there stories of
broken cranks quite a few years ago due to the removal of the long-nose
crank adapters without replacing them with a damper or something of equal
weight?
Beyond that, the wet-sleeve engine is a special case, I think. Fairly large
piston area combined with the cylinder spacing required for wet-sleeves,
along with three bearings, creates rather a large rocking couple, and those
vibrations are very pronounced within the working range of the average race
engine. The engine may be in primary balance, but the amplitude of those
second-order harmonics is pretty large until well beyond the maximum rpm of
the engine.
Anything to dampen those vibrations seems to me to be a good thing. (On that
note, had I the money for some serious experimentation, I'd be thinking
about the crankshaft as two halves separated by the center journal and would
be trying dampers on _both_ ends of the crankshaft....)
Cheers.
--
Michael Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking
distance....
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