Hi Phil,
interesting you are having visible vibrations. My engine doesn't show things
like this.
I guess the rear carb drops from a lack of flow. Maybe fuel supply is not
working properly, valve springs too soft with valve bounce.
Something like that.
To help the crank....making everything as light as possible:
Piston with rod - 1000gr
Flywheel with ring gear - 3500gr
Clutch with plate - 1000gr
Pulley - 400 gr
Seems to work fine. I let balance the crank all 2-3 years.
Cheers
Chris
-----Ursprüngliche Nachricht-----
Von: Fot <fot-bounces@autox.team.net> Im Auftrag von Phil Gott via Fot
Gesendet: Dienstag, 25. August 2020 13:50
An: Friends Of Triumph <fot@autox.team.net>
Betreff: [Fot] Crank Harmonics and Carburetion
Can anyone help with this weird phenomenon? The discussion of the second
harmonic being at 5200 rpm on the TR4 crank got me thinking:
On a chassis dyno we could watch the SU (HS 6) pistons during the dyno Pulls.
We started each pull at 3000 rpm. The pistons went all the way to the top
almost immediately after going to full throttle. The front carb piston stayed
all the way up for the entire run. The piston in the rear carb DROPPED DOWN to
about 3/4 open at around 5300 rpm and stayed there for the rest of the pull.
This repeated consistently.
As these depend on air flow via Bernouliâ??s law, I examined the valve train
thoroughly, fearing a stuck valve, problems with the valve train, a bad lifter
etc. but everything looked fine. No noises from errant valve operation either.
The crank harmonic discussion got me thinking. Could it be something to do with
vibration that would upset the air flow or cause the piston to drop? Note that
the piston was steady when it dropped. No apparent fluttering. Iâ??m stumped.
The car runs very strong nonetheless. You see the results in Daveâ??s latest
video at Thompson. He and I are thinking about putting a go pro camera and a
light under the hood to watch that carb in real life track situations to see
what happens.
Any thoughts as to why the Piston in the rear carb only should drop at about
5300 and above?
Phil Gott
Sent from my iPhone
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