Yanmar tach repairable?

[GerryL]

I’m on my second year of ownership with this boat. I’ve been wondering why I couldn’t reach rated RPM on this 3GMD. I just upgraded my charging system and I got a handheld photo optic tach to check alternator rpm (smaller pulley). After checking all that, I decided to put a reflector on the crankshaft pulley. To my surprise, the Yanmar tach is 100rpm low at idle, and 500 rpm low at cruise! So when I thought I was at 2500rpm, it was actually 3000. Still within rated rpm so no worries. My tach is the P=97 Nippon Seiki N-2. Are these able to be calibrated? Repaired? Thanks!

[GerryL]

Since there were no replies, I thought I’d post an update in case someone in the future runs into this. I couldn’t find info on repair or calibration. A new original tach was over $425! I couldn’t stomach that so I got an aftermarket tach from Hamilton Marine for just over $100. I’m now using an alternator tach output signal instead of the original sensor counting flywheel teeth. It appears to be accurate and working well.

[Tin Tin]

Good on you for reporting back.