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Smiths RVI Positive Ground Tachometer Bench Test ?

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... It will need to be checked against a external tach for accuracy and may need further calibration. Another time. At least it works now.

Calibration is a piece of cake. There should be a trimmer pot on the tach's CB--you'll need to drill a hole in the back of the case unless you want to do trial-and-error--and you just have to tweak it to calibrate. I calibrated mine with a Sears passive dwell-tach, and I've confirmed reasonable accuracy over the years using a gear ratio calculator. The gear ratio calculators take gear ratios, RPM and tire diameter and give speed; if you know speed, gear ratios and tire diameter you can solve for RPMs (i.e. you can 'close the loop').
 
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britishrich

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Calibration is a piece of cake. There should be a trimmer pot on the tach's CB--you'll need to drill a hole in the back of the case unless you want to do trial-and-error--and you just have to tweak it to calibrate. I calibrated mine with a Sears passive dwell-tach, and I've confirmed reasonable accuracy over the years using a gear ratio calculator. The gear ratio calculators take gear ratios, RPM and tire diameter and give speed; if you know speed, gear ratios and tire diameter you can solve for RPMs (i.e. you can 'close the loop').

Hi Bob, Thanks for the info. Yes it'll have to be another time as I ran out of that time yesterday, late day, and didn't have a separate tach with me. I have a nice dial-back timing light with digital tach built in but didn't have it with me. I was happy to get the tach finally working as the owner needed the car for Monday AM. Surprisingly, my ears told me the tach was reading pretty darn close to engine RPM. It was great to see that needle finally move.

Yes Mark's document had a nice writeup in there for calibration, and I need to drill a hole in the tach case to easily access the potentiometer(pic below) when I get the car back.

P1030009.jpg

Rich
 
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Also, the state of California thoughtfully places radar speed signs along the roads so that Healey owners can calibrate and cross-check their speedometers and, indirectly, their tachometers.
 
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