Tachometer - switching from sensor to alternator driven?

[Chachere]

Having ongoing issues with a dodgy tachometer on our Yanmar 4JH3-TE. Unfortunately, the flywheel sensor (which I think is the source of the problem, or the connections to it) is located in a spot on our Catalina Morgan 440 that is beyond horrible to access. Thinking perhaps we could get a different tachometer and drive it off the stator tap of the alternator (we have a Balmar series 60 and a Balmar 618 regulator, which appear to be set up for this). Would this work (assuming I can calibrate properly with a laser tach)? Any downsides?
T.I.A.

[FPNC]

The only downside would be that the MC618 regulator can shut off the alternator under certain conditions. When the alternator is shut off, the tach signal from the stator windings will disappear.

There is a device manufactured that is called a 'Tiny Tach' that can create a steady tach signal by reading the pulses of a single fuel injection line. This will give you a nice tach signal that is separate from the alternator output.

[cram]

Great answer above. The only thing I can add is that cleaning the flywheel sensor is an annual maintenance task on Yanmars that have one fitted...

How do you clean the exhaust elbow annually if you can't reach the back of the engine ?

The other possible source is the wiring harness starting to break down. The wiring is plain copper (not tinned). It tends to get stiff and brittle and may have been subject to corrosion. Check all the connectors and condition of wiring sheats/insulation.

[Chachere]

Originally Posted by cram

The only thing I can add is that cleaning the flywheel sensor is an annual maintenance task on Yanmars that have one fitted...

How do you clean the exhaust elbow annually if you can't reach the back of the engine ?

Thanks for responding. What do you use to clean the sensor?

(P. S. The engine is under the salon floor. I can reach the rear of the engine fine, it's the port side that's hard to get at, even with additional access ports I added)

[cram]

I remove it, clean off the dust/debris with a rag and then reinstall.

Can you reach that part from behind (same access as servicing the exhaust elbow)?...... 1st world problems! LOL