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Old 06-08-2017, 04:20 PM   #1
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Tachometers

I have a 1981 Californian with twin Perkins 4.236 engines. Having trouble with my tachs upper and lower helm. Currently I have a mechanical sending unit on the front of each engine. Wires come from the sending unit connect the tachs. The upper and lower helm tachs for a given engine are wired in series and back to the sending unit.

Question: Any one replace/upgrade their tachs if so what did you do for replacement.
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Old 06-08-2017, 04:48 PM   #2
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I'm working on gauge issues myself and have one of four tachs as an issue. In my research thus far, loose or corroded wire connections seem to be a common issue. If you haven't already done so, perhaps check those connections at the tach, sender, and buss bar (especially on the flybridge if it is more exposed to weather). That is what I'll be doing this weekend. Good luck.
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Old 06-08-2017, 05:52 PM   #3
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Should be in parallel, not series.

I like the VDO programmable tachs, vision series. Tachs once dialed in are dead nuts accurate. But the hour meters suck.

Before buying tachs, put a AC voltmeter on the tach signal terminals and make sure you are getting a few volts AC with engine idling. Half of tach problems are wiring problems. No signal AC, no reading.
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Old 06-08-2017, 06:01 PM   #4
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Quote:
Originally Posted by Stu-L View Post
I have a 1981 Californian with twin Perkins 4.236 engines. Having trouble with my tachs upper and lower helm. Currently I have a mechanical sending unit on the front of each engine. Wires come from the sending unit connect the tachs. The upper and lower helm tachs for a given engine are wired in series and back to the sending unit.

Question: Any one replace/upgrade their tachs if so what did you do for replacement.
Are these the Stewart Warner gauges with the pulse generator running off the PTO on the front of the engine?
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Old 06-08-2017, 07:02 PM   #5
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Wish I could help, but I've got dual tachs driven off the alternators. But they're not without problems, too.

Historically on my boat, the stbd tach was stable and the port would indicate 200 RPM lower and become erratic as the alternator loading decreased. Both lower and upper helm tachs behaved in unison. As a result, I always thought the stbd tach was my more accurate one.

After I installed my Balmar alt on the stbd side, I found that the old tach read 200 RPM higher than actual at cruise. (I used a digital tach as the truth system.) It turned out that the port tach was more accurate when the alternator loaded up. Now my cruise RPM is 1800 instead of 2000...for the same engine speed. Go figure!!

Recabling the alternator charges directly to each battery bank without the need for combining banks for charging also resolved the instability problem on the port side. Just one more of my boat's pecadilloes...but I love her.
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Old 06-08-2017, 09:32 PM   #6
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We too had tachometers that ran off the alternators. Always an issue when the batteries were charged up or the generator was on and the battery charger kicked in. Finally replaced them with tachometers that work off a sender that counts the flywheel teeth. Now all is well and the tachometers always work and they are accurate.
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Old 06-09-2017, 06:28 AM   #7
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We changed from Faria analog tachs to Aetna digital tachs. Ours happen to use magnetic senders, from a flywheel sensor. Dead easy installation.

Dunno if Aetna has models that might user your senders... but it might be worth a look, or even a query to them.

-Chris
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Old 06-09-2017, 08:46 AM   #8
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Only time I really use tachs is on fly bridge when idling to maneuver by using trany gears; because up there I can't clearly hear the twins purr in idle and want to make sure they are both in low rpm [under 1K - 6 to 8 is best]. At that low an rpm exact synchronization is not required

At different speeds [rpm] tach for one engine can read up to 200 rpm different than the other - when my my ears as well as synchronize light source tell me that both engines are turning at exact same rpm.

Therefore... I for decades felt that tachs are a fairly good approximation, but not an end-all gauge for how fast engines are actually turning. For me - ears work best with good synchronize unit as backup.

Happy RPM-Sync Daze! - Art
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