Charlie,
With 165x15 radial tires and the TD 5.125 rear axle gearing, the
roadspeed should be about 14.4 mph / 1000 rpm, giving you about 50.40 mph
at 3500 rpm if my chart is correct.
Have you checked the actual road speed against a known-good car or on
a measured mile? That will give you one accurate point of reference.
It's not unlikely that both instruments are in error.
A recent article in The Economist reported that in today's market, US
auto speedos are more accurate than EU auto speedos (EU speedos read
higher, it said).
Dwell tachs always have a low-rpm scale, and many have a high rpm
scale that would allow you to check at, say 2000, 2500, 3000, etc. A
fan belt that is too loose for the power requirements of the dynamo will
slip, but this reduces tach readings. A fan belt that is smaller than
the fat belt the engines came with may spin the dynamo faster if it rides
deep in the dynamo pulley and in normal position on crankshaft pulley.
If you don't get the information you need from others, let me know and
I'll measure the pulleys on my engine.
Bob
On Wed, 27 Nov 2002 18:23:45 -0500 Charlie Baldwin <ewsinc@BlazeNet.net>
writes:
> My tach on my TD seems to read high, at least from going through the
> math. At 50 mph indicated the tach says approx. 4000 rpm. The
> numbers
> on the tach reduction gear box on the back of the generator are
> "R.141/AT17 2-25:1". The tach face itself says Jaeger
> X65021/4
> RPM
> X 100
> 2-1
> K.45
> I've looked at another TD tach and it is the same.
>
> The pulleys under the hood/bonnet are 3 3/4" on the crankshaft and 3
> 1/4" on the generator.
>
> Does any of this seem incorrect?
>
> TIA
> Charlie Baldwin
> '52 TD
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