Re: How to check R.P.M.'s

Posted by Bob M on April 10, 2001 at 06:33:18 from (165.170.128.65):

In Reply to: How to check R.P.M.'s posted by Martin Caldwell on April 09, 2001 at 17:35:44:

Here's a lower-tech solution: Get yourself a so-called "hand tachometer", then stick it on the end of the belt pulley shaft to measure the belt pulley RPM. If you know the crankshaft to belt pulley ratio, simply multiply the belt pulley RPM by the crank to belt pulley ratio - the result will be the engine RPM.

If you don't know the belt pulley ratio, it's easy to figure out: First short the mag so the motor won't start. Then turn the motor with the hand crank; count the number and fraction of crank revolutions required to turn the belt pulley EXACTLY one full revolution. The result is the belt pulley gear ratio.

If you can't borrow a hand tach (most any older farmer who ever owned a combine will have one somewhere), check on EBay. Used hand tachs routinely go for about $20 - $30.

• EBay hand tach listing

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