Sorry about bombing, but maybe some one has the answer. Checking out
Lazarus' new 4.30 rear end showed up a nasty non-linearity in the
tachometer reading. It's close, but reads a bit low at sub-1000rpm, is
very close at 2000, reads 3500 at a true 3000, says about 4700 at a true
4000. (I quit there, that's fast enough for the statistics).
The non-linearity makes me feel quite certain that it's not a wrong
ratio in the tach-drive gearbox. I opened it up last night and
cleaned/degreased it. Stability improved, but not the error. When I had
it apart I noticed that there is a bridge across the framework at the
area where the face is attached by the two screws. The bridge consists
of two pieces separated by a small gap with a hole concentric with the
needle shaft. A small brass screw joins the two pieces. I'm guessing
that this screw could function as a calibration tool. Anyone out there
have any ideas on this?
The non-linearity makes me wonder about the spring. I do recall
from freshman physics that f=kx for linear springs. What's the function
for quasi-planar springs? is the torque a linear function of the angular
displacement? The pre-load on the spring can be varied by attaching the
needle after different amounts of rotation. If I had a spare tachometer
I'd start playing around, but right now I've got to make up for seven
weeks of not having my lbc fix.
Any and all help, advice, or sympathy will be welcome. (Even TS will be
accepted.)
Bud Krueger
52 TD "on the Road Again"
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