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Old 09-24-2017, 02:43 PM   #1
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tachometers

I have twin Yanmars diesels on my 34 Pilot. The tachs are fine at idle. They top out at 2800. Checking the from the flywheel its showing the correct 3200-3300. Both tachs are off, Anyone have any suggestions on what to do ?
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Old 09-24-2017, 04:47 PM   #2
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There adjustments on many tachs. The first gets it in sync with whatever sending system you have, then a tiny potentiometer to fine tune them.

My old VDOs were no longer taking an adjustment so I replaced them with new Farias.

One easily adjusted, the other I couldnt seen to turn the potentiometer and with a little harder push, the screwdiver punch right through. Back to warranty.

So be careful trying to adjust any of them.

But first...check all your connections in the positive, negative and signal wires.
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Old 09-24-2017, 05:22 PM   #3
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Originally Posted by Dennis G View Post
I have twin Yanmars diesels on my 34 Pilot. The tachs are fine at idle. They top out at 2800. Checking the from the flywheel its showing the correct 3200-3300. Both tachs are off, Anyone have any suggestions on what to do ?
Not electronic tachs?

Our boat came with analog tachs. They went south, so I had them rebuilt. They could be adjusted to be sort-of correct at one RPM level; for example, adjusted at 2000 RPM meant they were close, at 2000, but off some at 2600 and off at idle.

I replaced them with Aetna digital tachs. CruzPro also makes digital tachs, and maybe others do as well.

-Chris
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Old 09-24-2017, 05:23 PM   #4
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Are they driven by the alternators with v-belts?
Belts tight?
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Old 09-24-2017, 08:32 PM   #5
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Are they Yanmar tachs? What model Yanmar engine?
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Old 09-24-2017, 09:44 PM   #6
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My last boat had digital tachs, and boy did they make it easy to set the RPMs the same for both motors. I may have to put them on my new boat too. Super accurate and easy to read.

Cheers, Bill
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Old 09-25-2017, 07:43 PM   #7
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Are these electronic tachs driven by the alternator or a sensor attach to the crank pulley?
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Old 09-26-2017, 08:02 AM   #8
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Are these electronic tachs driven by the alternator or a sensor attach to the crank pulley?

Our Aetna digital tachs are driven by a magnetic sensor on the flywheel. (As were our original analog tachs.)

Think Aetna also has other models, though...

-Chris
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Old 10-18-2017, 10:57 AM   #9
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Are they driven by the alternators with v-belts?
Belts tight?
Yes
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Old 10-18-2017, 10:58 AM   #10
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Are they Yanmar tachs? What model Yanmar engine?
No Faria
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Old 10-18-2017, 11:03 AM   #11
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Look at the back of the tachs and see if they have an adjustment screw.
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Old 10-18-2017, 12:59 PM   #12
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No Faria
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Look at the back of the tachs and see if they have an adjustment screw.
The Faria Chesapeake series tachs we had originally did have two adjustment screws, one for course dial-in, and then a second one for a finer adjustment.

That said, we could only get the "right" (-ish) at one RPM level, so setting at 2000 meant they weren't all that perfect at 650 (idle) and 2300 (WOT).

That partly drove our change to digital tachs.

-Chris
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