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Author Topic: Tach calabration  (Read 708 times)
Gordie Allen
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« on: March 08, 2013, 05:47:19 PM »

I want to calabrate my electronic tach running of the alternator.  I read a DIY article on how to use a handheld fluorescent bulb and white tape on the crank pulley to determine rpm.  The fluorescent pulses at 120 Hz, so the tape should appear as 4 stationary points on the pulley at 1800 rpm.  My problem is I can't get a direct face-on look at the crank pulley.  I can; however, get a face-on of the pulley on the generator shaft that now runs the alternator.  Does anybody know how fast it turns in relation to the crank?
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Augusta, MI
1956 4104
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lostagain
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« Reply #1 on: March 08, 2013, 06:12:38 PM »

The best would be to get a hand held tachometer. They can be had fairly cheap now at stores like Harbor Freight. You will also use it to calibrate the idle speed and the governed high speed at tune up time. So a good tool to have.

JC
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JC
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« Reply #2 on: March 08, 2013, 06:22:32 PM »

On a DDC, V type, depends where the alternator drive is driven from, off end of cam, same as engine rpm, if off the blower drive, same speed as the fuel pump, is a goofy ratio, can be different ratios, for get that one. as mentoned, a strobe tach or a mechanical tach, but tuff, keeping eye on watch and readout.
Go with the simple hand held using th strip of take on the damper pully.
Easier than it sounds.
Dave M
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Gordie Allen
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« Reply #3 on: March 08, 2013, 07:12:32 PM »

lostagain,
Thanks, I didn't realized a hand held tach was so cheap.  Going to Harbor Freight tomorrow.
Gordie
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Augusta, MI
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luvrbus
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« Reply #4 on: March 08, 2013, 07:19:14 PM »

The H/F cheapo is a contact tach be sure you can reach where ever you are going to read from
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Lin
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« Reply #5 on: March 09, 2013, 07:38:47 PM »

I assume that you are talking about a photo tachometer.  I believe that one I have was around $20.
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luvrbus
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« Reply #6 on: March 10, 2013, 07:46:43 AM »

Those are about the same as the contact type Lin they are not good for over 8 inches from the tape depending on the light sometimes 1-1/2 inches
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Lin
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« Reply #7 on: March 10, 2013, 08:54:43 AM »

Thanks for the info Clifford.  I do not remember how far from the tape we took the reading, but it was not so close as 1.5 inches. I'm pretty shy of getting close to that belt.
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« Reply #8 on: March 10, 2013, 09:18:47 AM »

That is 2 of us Lin those belts love shirt sleeves BTDT 
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