Hello -
I would like to measure the RPM of my type 4 engine, but I don't have a tachometer.
I do however have a digital multimeter which can measure frequency. In this mode it displays the frequency of an incoming signal in Hertz.
I am assuming that I can measure RPM with this meter as follows. I connect the frequency counter to the LT side of the ignition coil. When the engine is running, the frequency displayed is the frequency at which the coil is being energised. This is exactly four times the frequency at which the engine is completing a full revolution, since there are four spark plugs each firing once per engine revolution. To calculate the RPM I would therefore first divide the frequency by 4 and then multiply by 60 to give the rotations per minute of the engine.
Did I get that right?
Leo