Tachometer not correct

[Zowie]

Suddenly by helm tach is over-stating my RPMs by approximately 500 -750. I normally motor at 2400 but now I must push it to about 3000 to get the correct performance. Not sure what caused this, but is there a way to recalibrate the tach?

thanks

John Z.
"Outstanding"
2008 Catalina 350 MKII

[nybor]

Hmm. not sure why it would all of a sudden do this. It is easy to calibrate it. All you do is get a wireless tach (Harbor Freight!!) put a piece of reflective tape on the flywheel (the tape comes with the meter) then see how the analog tach compares to the digital one. On the back of the tach is a small set screw (pot) that you can adjust to mirror your digital flywheel readings.

But, unless the tach was failing.......not sure it is the problem.

I first thought that something had fouled your prop (piece of debris, critters, etc.) requiring a higher rpm to maintain speed.

Nybor

[Pgtjs]

Hi there,

I had the same problem some years ago. It started flickering and became wildly inaccurate. But by accident I turned on the blower fan and it returned to normal. It has been fine ever since but reverts to flickering all over the place if I turn the fan off. So I let it run all the time. I have a Yanmar Diesel - factory installed - and have no idea if the wiring harness was changed in some way back when it was built in 2006.


Cheers, Geoff.

[nybor]

Forgot to mention (Leigh mentioned this first). If I leave my solar panels on, the tach will not work. As soon as I turn them off, works fine.


dave

[Carolina.Mind]

Did you change alternatos?

[nybor]

nope. The original one worked fine.

[leigh weiss]

If you tach is the same one I have with the M35B engine, I have found that the rotary switch (A,B,C,D) on the back of the tach. and or the trimmer pot (screwdriver slot on the rear of the tach) some times they get dirty and require some movement to clean the internal contacts. I assume that all the connections including the ground wire are correct and corrosion free on the back of the alternator and the wire harness behind the dash.
Another cause might be one of the internal diodes has opened (failed) giving lower output voltage and less pulses/rev.
You can check this by observing the max voltage (14.2) output from the alternator.
Or.... the tach has failed!!!
Let us know how you solve the problem.

[TBOT422]

OK, So where is this calibration screw? I have a similar problem with the tach being erratic and I found I could tap on it and it would return to normal. I took off the panel, removed each wire, cleaned and replaced them. I ran the range setting screw through all of its settings and returned it to its original 'B' setting. Tach seemed better, but now read 1500 RPM at idle. If I tapped on it pretty firmly it would jump around to other numbers sometimes 0. There is a small hole in the back of the tack labeled CAL, which I assumed was the calibration screw. Couldn't see in the hole very well but attempted to insert small screw driver (both straight and Phillips), and nothing appeared to change as I turned the screwdriver. Shining a light in the hole there did not appear to be anything there, so I decided to insert a tooth pick which went all the way in without seeming to touch anything. So either this is not the calibration screw hole, or my calibration screw has fallen out and is rolling around somewhere in the boat.

Any ideas?

[TBOT422]

I have confirmed that the adjusting screw in the back of the tach is missing on my tach. Apparently it fell out at some time. From some research I have done, it appears to be a #8 set screw of some sort (the manual says it is adjusted with a 5/64 hex wrench). Is there any likelihood that I can just insert a new #8 set screw into the back of the tach and succeed in calibrating my tach? Any suggestions on how long a screw I should try to use?

Other information that may prove to be useful is that the part number for the Universal factory tach is 011917. Cost is around $300-$400. I have found an alternate Faria Part #32834 which Marine Parts Source claims is a substitute for $111. http://www.marinepartssource.com/newdet ... 0Hourmeter

If I have to replace the tach, I'm not sure there is any means to adjust the hour meter, so I could end up with a C350 with some really low hours!!!

[Aussie Mate]

Gary: attached are two pictures of the back of my tachometer if that helps you at all. Sorry, did not remove the screw for fear of consequences.

[nybor]

Hi. I have an extra tach you can have. I replaced the entire suite (all of the instruments), so the tach is fine. Let me know and I can mail it to you.
I am pretty sure I still have the glass cover and o-ring for it.

dave

[nybor]

forgot to mention. the replaced tach had zero hours, so I bought a remote tach and placed it in the engine compartment. Very easy to hook up. But before that I applied 12 volts (maybe less, don't remember) and let it run up to 420 hours.

[TBOT422]

Dave/Bruce,

Thanks for the replies.

I downloaded the Westerbeke Service Bulletin #148 http://www.westerbeke.com/mdtools/servi ... sb_148.pdfoutlining diagnostics for the tachometer. I'm going to verify this week that I have the proper AC voltage at the back of the tach. If so, I bought a #8 set screw 3/8" long (for 45 cents!!) that I will attempt to reinstall in the calibrate hole and see what happens. Wouldn't that be a hoot if it worked!! If that doesn't solve the problem, then I will replace the tach. Dave, I will let you know if I'm interested in your spare tach. Thanks for offering.