Still need Tachometer help{interchangeability}

Will a Tach from a 4cyl 4-stroke Mercruiser work on a 2cyl 2-stroke OMC outboard? Seems like the number of pulses per crankshaft rev would be the same, but don't know if there are other considerations. What about Tachs from a 4cyl and 6 cyl 2-stroke? Have these "spares, and don't want to buy a new tach for my 2 cyl OB if I can make one of these work.

Re: Still need Tachometer help{interchangeability}

A Mercruiser use the same ignition type as does a car and the pulse is derived every time the coil generates a pulse. This means on one coil units there is a pulse every other cycle per cyl. You are right about the numnber of pulses being the same. However, the outboard uses the stator for the pulses and is a different source though the same number of pulses. The tach lead on the OMC outboard on the rectifier assembly which is the same as one of the yellow stator leads may be used for the pulse lead and most probably will work. To help locate this lead locate the two yellow leads comming out under the flywheel. Notice this goes to a rectifier with a red lead going to the battery and the two leads I am talking about. One of the two yellow leads will have another wire connected to it. This is the pulse or tach lead appearing here and going up to the controls. Go ahead try it. The tach needs 12V and grnd and this pulse lead.

Re: Still need Tachometer help{interchangeability}

Thanks Ron Davis. Makes sense to me.

Re: Still need Tachometer help{interchangeability}

Just to add so you will know. Mercrusier uses DC voltages and two strokes use AC voltages to run the tach.