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Posted by D. Sherman [24.32.202.83] on Tuesday, January 19, 2010 at 01:21:46 :
In Reply to: Yes but.... posted by Chriscase [76.201.17.246] on Tuesday, January 19, 2010 at 00:14:20 :
Tachs don't usually hook up to a spark plug wire. They hook up between the coil and the points, thus they see 1 pulse per spark.
Now, the really fun way to measure an engine's RPM is with a strobotach. You turn the dial until crankshaft pulley appears to stand still, then read the RPMs of off the dial. The reason it's fun is that by adjusting the strobe rate to be just slightly off from the "stand-still" speed, you can make it look like everything is turning very slowly. Where it even gets better is if there's a vibration somewhere -- you can tune it until you can watch the vibration slowly moving back and forth. Fan belts, for example, always "flop", and with a strobotach, you can see just how much flop there is, and where. They're not all that accurate for absolute speed measurements but they're great for getting close quickly without having to connect anything to the machine, and they're great for visualizing exactly what is going on.
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