Change gearing in generator vs changing tach 1960
11-27-2011, 11:01 AM
#1
Change gearing in generator vs changing tach 1960
Could this be done?
I really don’t feel like taking out the cluster again. Especially after I repainted the cluster and steering bell. Although the rebuilder has agreed to send me another tach I am not looking to take the cluster out.
Last winter I had the tach rebuilt for a generator, and the readings are not close. Before the tach was rebuilt I made sure that it was for a generator.
Could the gearing in the generator be changed to compensate for a tach not reading right? Are there different size generator gears?
Enclosed are the readings from the tach. The tach readings are almost double of the digital readouts.
Digital timing - Tach
Light
830 1500
1000 1700
1400 2500
1800 3400
2000 3700
2200 3800
2400 4600
I really don’t feel like taking out the cluster again. Especially after I repainted the cluster and steering bell. Although the rebuilder has agreed to send me another tach I am not looking to take the cluster out.
Last winter I had the tach rebuilt for a generator, and the readings are not close. Before the tach was rebuilt I made sure that it was for a generator.
Could the gearing in the generator be changed to compensate for a tach not reading right? Are there different size generator gears?
Enclosed are the readings from the tach. The tach readings are almost double of the digital readouts.
Digital timing - Tach
Light
830 1500
1000 1700
1400 2500
1800 3400
2000 3700
2200 3800
2400 4600
Last edited by stratplus; 11-28-2011 at 01:20 AM.
11-27-2011, 11:54 AM
#3
Race Director
You can have an inline ratio adaptor built by a speedo shop and mount it behind the generator. probably cost you about $100.
Doug
Doug
11-27-2011, 02:36 PM
#4
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You either have a tach head for a distributor drive, or a WAY wrong (much too small) generator pulley; your pulley should be 3-3/4" in diameter. 
11-27-2011, 04:47 PM
#5
Melting Slicks
I seriously doubt he is successfully running a 1.9" generator pulley...........
Or a 14" balancer pulley.
Did the tach every work at all before it was sent off???????
From what I understand there are no different parts, just different calibration for the two styles. And the dist tachs are marked something like half speed.
Looking forward to finding out the answer!
11-27-2011, 04:50 PM
#6
11-27-2011, 04:54 PM
#7
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11-27-2011, 08:08 PM
#9
Melting Slicks
11-27-2011, 08:30 PM
#10
Le Mans Master
Jim
11-27-2011, 10:53 PM
#11
Le Mans Master
The 3 3/8 pulley will spin the Generator a bit faster (good for charging) but this only translates in about 100 RPM greater reading at the Tach than the correct 3 5/8 pulley. I ran a bunch of tests last year when I was playing with voltage regulators, Generators and had the Tach repaired. I agree with John Z, your Tach was likely calibrated for a distributor rather than a Generator. If you want it fixed correctly, it has to come out. 
Pilot Dan
Pilot Dan
Last edited by Pilot Dan; 11-27-2011 at 10:55 PM.
11-28-2011, 07:36 AM
#12
Melting Slicks
Believe the appropriate term here is "effective diameter". John Z is again on the mark. It is akin to the average diameter of the belt on the pulley.
My 60 tach ran about 10% high for 30 years, even after a rebuild. Turns out it had a 3" pulley on it which must have gotten put on during a rebuild 30 years ago. I located a 3.4" pulley at a generator rebuild shop going out of business, it works fine.
Good news is that this all happened when I swapped out a 3.36 rear for the original 3.70 posi unit, and the speedo had always been 10% low. So after all that time I finally got my tach and speedo back correct again.
My 60 tach ran about 10% high for 30 years, even after a rebuild. Turns out it had a 3" pulley on it which must have gotten put on during a rebuild 30 years ago. I located a 3.4" pulley at a generator rebuild shop going out of business, it works fine.
Good news is that this all happened when I swapped out a 3.36 rear for the original 3.70 posi unit, and the speedo had always been 10% low. So after all that time I finally got my tach and speedo back correct again.
Last edited by toms silver 60; 11-28-2011 at 07:43 AM.
11-28-2011, 08:43 PM
#14
Melting Slicks
one more thing
I would disconnect the cable until you get situation corrected. You might damage something internally when you rev it up and needle goes way beyond normal travel.
11-28-2011, 10:44 PM
#15
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The way I fixed that problem with my car was to put a 4in pulley on the generator.
Another plus is that the generator charges fine, AND, it keeps gen rpm down.
The 4in pulley came on some hi-perf engines (such as FI) as well as some truck generators. The reason some trucks got the 4in pulley is because they had very low geared rearends which kept the rpm's high on truck engines, so a 4in pulley kept gen rpm's slightly lowered.
Tom Parsons
Another plus is that the generator charges fine, AND, it keeps gen rpm down.
The 4in pulley came on some hi-perf engines (such as FI) as well as some truck generators. The reason some trucks got the 4in pulley is because they had very low geared rearends which kept the rpm's high on truck engines, so a 4in pulley kept gen rpm's slightly lowered.
Tom Parsons
Last edited by DZAUTO; 11-28-2011 at 10:54 PM.
