Tachometer died on Yanmar 2GMF

[Kupe]

Hey gang-

Yesterday the tachometer on our 1984 Tartan 28 stopped working. The engine is a Yanmar 2GMF 13hp.

I didn't have time to do much troubleshooting, but did take a quick look in the lazarette and didn't see anything loose or detached at the rear of the tachometer. And of course I gave the tach a scientific finger tap-tap with the engine running, but it stayed right at zero.

Well- mostly that is. At what I estimate to be around 2,000 rpm, the needle bumps up to indicate maybe 150 rpm or so. The instrument itself is a Nippon Seiki N-2 P=97

So, any thoughts on where best to start my search for the culprit?

Thanks gang!

Kupe

[_andi_]

Most tachs get their signal from the alternator. I'd start with the alternator belt, it slipping could be the problem.

[Kupe]

Originally Posted by _andi_

Most tachs get their signal from the alternator. I'd start with the alternator belt, it slipping could be the problem.

Thanks Andi. What I learned in another thread is that apparently the Yanmar 2GM series engines use a sensor off the engine flywheel to the tach, not the alternator.

Does anyone know if a multimeter can be used to check the output to the leads going into the tach? That would seem to be a good way to determine if the fault was in the instrument itself, but I don't see that mentioned in any tach troubleshooting info I can find.

[bigdogandy]

I believe you can use an ohmmeter to check the tach sender at the flywheel housing.....put the leads across the terminals and if you get any reading at all the sender is most likely OK. Definitely check for loose connections at both ends of the circuit, clean the terminals, and make sure the ground is secured. I believe it is fairly uncommon for the actual tach to die.

[kenbo]

The tach on this Yanmar doesn't get it's signal from the alternator but rather from a sensor on the flywheel housing that corresponds to the number of teeth on the ring gear. In this case P=97 so 97 pulses per revolution. http://j30.us/files/YanmarGM&HMWorkshopManual.pdf read page 198 for testing procedures for the sender and tach.

Good luck.

[JimsCAL]

Pretty sure the output from the sensor is a stream of pulses that vary in frequency as the engine speed changes. The sensor is magnetic and generates a pulse each time a tooth on the flywheel passes it. A DMM with a frequency function could check what's going to the display.

[Kupe]

Originally Posted by kenbo

The tach on this Yanmar doesn't get it's signal from the alternator but rather from a sensor on the flywheel housing that corresponds to the number of teeth on the ring gear. In this case P=97 so 97 pulses per revolution. http://j30.us/files/YanmarGM&HMWorkshopManual.pdf read page 198 for testing procedures for the sender and tach.

Good luck.

This place is amazing! Thank you Kenbo!

[kenbo]

You're welcome, but as Bigdogandy said, make sure all the connections are clean and tight on both the sender and tach. More than half the time that's the problem.

[sailon46]

FYI, when my tach died on my previous boat Catalina 42 the culprit was a small water leak from the exhaust elbow of the Yanmar right on the sensor on the flywheel.
Once I retightened the clamp the Tach worked again with no problems till I sold the boat.

Ernie on the Mary Jane

[ZULU40]

Usually its the tach electrical connections, minor corrosion jamming the signal. Learn to use a multimeter to diagnose which one, or be lazy and just clean them all.

[Cadence]

Originally Posted by kenbo

You're welcome, but as Bigdogandy said, make sure all the connections are clean and tight on both the sender and tach. More than half the time that's the problem.

The distance between the pickup and flywheel or just crud in the gap to the reluctor and flywheel could be it.

[brucebach]

I had the same problem and it was just the two spade connectors going to the sensor at the back of the engine/front of the transmission (flywheel as stated above) were a bit loose. Squeeze the female ends lightly with pliers, sand the male ends, and hopefully you’ll be back in business.

[sailorboy1]

Both my boats with Yanmar have had this problem. Each time it’s corrison either on the pickup wires or at the engine wiring harness

[Compass790]

i think our YSM8 has the same setup as yours & we've had the same problem. As other posters said culprit was bad spade connectors on flywheel sender & next time loose plug in wiring loom. Easy fix. Let us know what the culprit turns out to be.

[Kupe]

Hey gang-

Huge thanks again! Finally got back to the boat and did the diagnostics in the manual that Kenbo posted. Thank you again Kenbo! Tach sender checks good and signal from engine to tach checks good. Wish it had just been dirty connections, but I guess that would have been too easy! ;

Soooo, I have a dead tachometer instrument. I'm inclined to go path of least resistance and simply put in the OEM tach. So who is everyone's favorite Yanmar parts supplier? I need tachometer part # 128170-91100. I get a few hits on the web, but less than you'd think.

Thanks gang!

Kupe