I have a Westerbeke 33 with what appear to be the original alternator and tach. Thing is, the tach will run up to 3600 rpm but the Westerbeke 33 manual says it has a max rpm of 3000.
It’s just a curiosity but I would be interested in your thoughts.
Paul M
NS30U #211, Sandpiper
Cowichan Bay, B.C.
Tach, may need to be adjusted, most are adjustable..
On a different boat, with a Yanmar engine, the tach sometimes acted erratically. The solution was to clean contacts, and replace the tach wire. Could be all you need to do is clean wire connectors, and if needed, a new wire. Fairly easy to do.
Cheers,
Don
‘87 NS30U #369 Breezin’
It’s not erratic at all, actually very steady. I’m thinking I should check with a strobe tachometer at the coupling and multiply by the reduction of the gear before I adjust it. Mitsubishi has lots of engines that run at 3600.
I’m not clear as to which Item the manual says it has a max of 3000. The engine or the tach??
Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA
The engine Joe.
Paul,
The manual for the W27 also lists the engine max as 3,000 RPMs. It was never clear to me if the 3,000 was the fastest the engine COULD go or SHOULD go.
I’ve been assuming that I should generally run the engine at 80% of max.
Jim Cosgrove
FATE 30U #343
Galesville, MD
I’ve had several Diesel engines and this is the first time I’ve been able to easily rev beyond the rated max. It just strikes me odd particularly because the tach shows a very common Mitsubishi max rpm. I’m wondering if someone reset the governor at some time in the past. I run at 2500 + or - most of the time so I’m not very concerned but I am curious.
In my experience it is not unusual for a diesel to have a higher unloaded rpm (high idle) than full load rpm but it may only be 1 or 200 rpm.
It is much more likely that the issue is with the tach than the engine. A quick check with an optical tach would quickly confirm this.
Most tachs are adjustable, check to manual.
Mike Jennings.
NS005 Chancy.
Port Moody BC.
Thanks Mike.
I’ve set lots of tachs, usually by running full throttle / no load for a few seconds while I adjusted the dial to the rated max. This is different in that Mitsubishi (W33 is a Mitsubishi) seems to like both 3000 and 3600 as max rpm ratings. Sometimes they govern the same engine differently for different uses like propulsion or generator or just to produce different Hp with the same engine.
…. but you’re right, the only real answer will come from a strobe tach. I’ll see if I can find one to use.
Hi Paul,
Could you also aim the strobe tach at the crankshaft pulley and then not have to do the reduction drive calculation?
I just checked and you can actually get an app for your iPhone to use it as a strobe tach! There are also apps of android phones.
Peter Moodie
Nonsuch 30U Catalyst #366
Sidney, BC/Winnipeg, MB
Great tip Peter! I should have known there would be an app. 
I will look right now.
I just said the coupling because it’s so much easier to get at with the vee drive and the math is pretty simple.
Update: I found a phone app but it wasn’t workable so I bought a cheap laser point and shoot counter. It worked perfectly and easily.
Bottom line: My engine is 3000 rpm as advertised and the tach was off. I adjusted it to the proper range but may replace it anyway because it seems a little sticky.
I would remove and clean the several connections that make the tach work, including the one on the alternator and the ground for the engine gauge assembly before doing anything..
Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA
Thanks Joe. Already checked them. Pretty sure it’s the tach but it’s not bad at all really.
If it is not the stock alternator the tach will most likely need to be adjusted. There are plenty of phone RPM apps that will get you close…
It is the stock alternator and tach Thor. I tried a phone strobe app but it was cumbersome and nowhere near bright enough. The laser ($26) works perfectly and waaaaay easier.
Check the voltage at the Tach. Should be 12v at least. DO NOT ground to the alternator. Low voltage will cause errors and most likely is corrosion in the connections.