On Sat, 11 Jan 1997 JDRPDX@aol.com wrote:
> I've just gotten my TD back from a considerable amount of engine work
> and, among other things, I purchased the gear and the cable that
> connects the back of theeen the generator to the back of the tach. The
> mechanic who helped rebuild the engine since heard the engine running
> and said that the tach must be incorrect in that the revs as shown on
> the tach were considerable higher than the probable actual RPMs of the
> engine.
>
> Is this possible? Is there an adjustment somewhere to bring the TAC
> readings in line with the actual revs of the engine?
It's easy enough to test the accuracy of your tach. Connect an electronic
tach and compare its readings to those of your TD's tach.
It isn't unusual for a generator-driven tach to read high. As the
generator pulley wears, the belt rides deeper in the worn pulley than it
should, in effect reducing the operating diameter of the pulley. That
wouldn't matter if the generator pulley and crankshaft pulley wore at the
same rate, but they seldom do. The generator pulley usually wears faster
than the crankshaft pulley, upsetting the original drive ratio. This
makes the generator spin faster than normal relative to engine speed, and
so the tach reads high.
A replacement generator pulley is the solution, if one is available, or
have the tach recalibrated to give a true reading with the worn pulley.
Of course, a mis-calibrated or worn tach could also be the root ofd the
problem.
-----------------------------------------------------------------------
Chip Old 1948 M.G. TC TC6710 NEMGTR #2271
Cub Hill, Maryland 1962 Triumph TR4 CT3154LO (daily driver)
fold@mail.bcpl.lib.md.us
If cars had evolved as fast as computers have, by now they'd cost a
quarter, run for a year on a half-gallon of gas, and explode once a day.
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