Tachometer calibration????
11-14-2008, 08:12 PM
#21
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The fine tuning , by moving the regulator, affects the tension of the hair spring and this of course will position the pointer higher or lower. If for example, you are reading 200 rpm high at say 3500 rpm, you can move the regulator to make it read where it should be. Problem is, now with more spring tension, it will read low at the bottom end. The regulator is only meant to fine tune after the proper procedure of magnetizing and demagnetizing are completed. Again, I would leave it alone.
11-14-2008, 08:14 PM
#22
Le Mans Master
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The fine tuning , by moving the regulator, affects the tension of the hair spring and this of course will position the pointer higher or lower. If for example, you are reading 200 rpm high at say 3500 rpm, you can move the regulator to make it read where it should be. Problem is, now with more spring tension, it will read low at the bottom end. The regulator is only meant to fine tune after the proper procedure of magnetizing and demagnetizing are completed. Again, I would leave it alone.
11-14-2008, 11:18 PM
#23
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St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I agree too, it's way to close to worry about taking it out!
Willcox
Willcox
Last edited by Willcox Corvette; 11-15-2008 at 11:15 AM.
07-09-2021, 04:36 PM
#24
I have the instrument cluster out of my '64. I've calibrated the spedo and figured I would check the tach calibration. Does anyone know the correct tach cable RPM to tach needle reading?
07-09-2021, 08:51 PM
#25
Instructor
Why would you test a tachometer with math instead of another tachometer? Too many variables to accurately determine with math. Tire size +/-, gear ratio +/-, speedometer gear +/-, correct reading on tachometer dial +/-, clutch slippage, etc. Your tachometer could be dead on right now, but the accuracy of your other inputs and decimal point rounding could give you a false answer.
07-09-2021, 09:25 PM
#26
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Count the teeth on the dist shaft gear and the driven gear. Provide this information to an experienced speedometer shop and they should be able to provide a calibration table. From there you can decide whether to make corrections to the head's magnetic flux.
It can be tough to get the tach dead on at all speeds due to some combinations of offset and gain error, but my recommendation is to get it as accurate as possible at the top of the rev range and don't worry about idle speed accuracy. When doing maintenance work that requires accurate idle speed use a good test tach.
Duke
It can be tough to get the tach dead on at all speeds due to some combinations of offset and gain error, but my recommendation is to get it as accurate as possible at the top of the rev range and don't worry about idle speed accuracy. When doing maintenance work that requires accurate idle speed use a good test tach.
Duke
Last edited by SWCDuke; 07-09-2021 at 09:28 PM.
07-11-2021, 09:03 AM
#27
I found the answer. Since the distributor spins at half the engine RPM, you multiply the cable RPM times 2. Or, tach reading = cable RPM x 2.
Luckily mine was dead on at 4000 RPM and a little off higher and lower than that. I can live with that.
Luckily mine was dead on at 4000 RPM and a little off higher and lower than that. I can live with that.
