Tach Reading

[Kevin S.]

I just rebuilt my 1961 283 dual quad 245hp motor. I now have some minor glitches to clear up.

The tach wasn't working - and I just replaced the internal tech gears in my generator.

The tach is now working after replacing the internal gears - but the tach now reads at roughly twice what I think the RPM's should be at.

I am thinking the generator pulley may be the wrong diameter. What size should the pulley be for a non-fuelie car?

Any other suggestions for me ?

Thanks,
Kevin

[Jim D.]

Re: Tach Reading

The pulley should be 3 5/8" O.D. The tach for a F.I. car, driven by the distributor, reads twice the cable speed. The gen. driven tachs. read the cable speed. Sounds like you have the wrong tach.

[John H.]

Re: Tach Reading

The tach is now working after replacing the internal gears - but the tach now reads at roughly twice what I think the RPM's should be at.

I am thinking the generator pulley may be the wrong diameter. What size should the pulley be for a non-fuelie car?

Any other suggestions for me ?

Thanks,
Kevin

Kevin -

Is there anything ink-stamped on the back of the case on your tach? It should have "Reads cable speed" (for a generator-driven tach) or "Reads twice cable speed" (for a distributor-driven tach). With your setup, the crank pulley drives the generator at twice crankshaft rpm, and the reduction gearbox on the back of the generator drives the tach cable at 1/2-generator rpm, which is back to crankshaft rpm. As Jim noted, it sounds like you have the tach for a distributor-driven setup, which is calibrated to read twice cable rpm instead of cable rpm.

[Kevin S.]

Re: Tach Reading

Thanks for the replies guys. The tachometer is the original low horsepower unit. But the generator was replaced by the previous owner. So I was thinking the problem was from the generator, the gears in the generator, the size of the pulley on the generator or the size of the pulley on the engine block.

What do you think ?

Kevin

[William C.]

Re: Tach Reading

Doubling the rpm is too much of a coincidence for pulley size to come into play, and to my knowledge there is only one set of gears for the gen drive setup. That leaves you with incorrect tach or inproperly calibrated tach.

[Kevin S.]

Re: Tach Reading

yes, thanks. perhaps the tach is on the fritz. it may be time for a new one. thanks for the replies

[Dick W.]

Re: Tach Reading

You can send it to instrument restoration shops such as Joe Ray, a frequent poster here.