Tachometer reading 50%

[Sam Curry]

I have a Yanmar 2GM in my 1983 Hunter 30. It suddenly began reading at 50% of proper reading. Where should I begin to look and what should I look for? Would appreciate help. ( I know I can multiply the reading by 2!!) Also, I have read in the archives about combination tach & engine hour meter. Is this easy to do? What is involved mechanically and parts wise?? Where do I get detailed info on the parts required?Thanks,

 

[steven f.]

alternator wires

First of all let me say I'm no 12 volt expert. I recently had a problem with all my panel guages giving me incorrect readings, the worst was the tach. I was scratching my head on this one and even tried cleaning all the wires and connections behind the panel, nothing. Than one day while doing something unrelated I noticed a ground wire from the back of the alternator was bearly attached to its grounding point. I repaired the ground and all in my world was working like a charm again. Seems like the engine panel guages are dependent on a good ground. Good luck.

 

[red coles]

perhaps

If your tach is driven by the alternator, it is possible you have a def. alt.(open or grounded field). You can remove and take to automotive electrical repair shop and they can test it. As to hr. meter, why not just add one. It's only a digital hr. counter, that is turned on by the ignition sw. Good luck red

 

[William Berson]

been there, done that

Been there a number of times on 2 different boats. Each time tach reads 1/2, then eventually reads 0. Problem was always the sender connection at the engine, which tends to shake loose as the motor vibrates at low RPM, check the connector at the engine end.

 

[Paul]

Tachometers don't use boat electricity

A tachometer is a little generator, and the guage in the cockpit (what we call "the tachometer") is an ammeter. The faster the little generator spins, the more current it creates, which makes the guage needle go higher. The tachometer armature probably has two sets of wires wrapped around, and one of them is fried. Therefore it generates half of the current.However, it could be the guage or it could be a high-resistance connection, who knows? But since you have this exact fractional reading, my money is on the tachometer (sending unit) itself.

 

[J Stage]

Magnet gone

If your Tach has a wheel at bottom of boat, one magnet has probably broken off.