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Old 10-04-2013, 08:28   #1
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Tachometer replacement for Perkins 4-236

The tachs for my Perkins 4-236 engines function by a pulse coming from the alternator to the tach itself. This is not too satisfactory, because when the batteries are fully charged (as they usually are when I first start up the engines) the tachs do not work, since the alternator is not putting out current to the batteries. This would not be too bad in the slip, but continues for quite a while after getting underway.

So I am thinking about replacing them. Aetna engineering seems to have some nice ones which their website says will work with my engines and connect to an SAE type mechanical drive fitting.

Does anyone have any experience with this that they would be willing to share?

Thanks,
John
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Old 10-04-2013, 09:12   #2
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Re: Tachometer replacement for Perkins 4-236

The simple fix is to turn on your running lights when you start your engines.

If you want to spend money, look at a Tiny-Tach.
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Old 10-04-2013, 10:03   #3
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Re: Tachometer replacement for Perkins 4-236

Hmmm. Thanks for that information. I'll try the running lights trick next time I take the boat out. I looked at the Tiny-Tach website. Doesn't seem like all that much money involved in a couple of them. Cannot say as I understand how they work though. "The Tiny-Tach tachometer is a $95 replacement tach any boat owner can install easily. The transducer mounts outside a fuel injection line . . ." Surely they do not calculate the RPM's based upon the fuel flow!
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Old 10-04-2013, 10:30   #4
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Re: Tachometer replacement for Perkins 4-236

The Tiny-Tach transducer clamps on the outside of an injector line and is triggered by the pressure pulse to the injector. According to the reviews I have found, they work well, but the display is subject to moisture and sunlight issues--I wouldn't want to install it on the flybridge. The tachs in the YC's GB32 are going out and I'm thinking of installing one inside there. Anyone else have any experience with them??
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Old 10-04-2013, 10:45   #5
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Re: Tachometer replacement for Perkins 4-236

Yeah, I found a review on them which discussed the moisture issue as well as the sunlight problem. They look intriguing, though. Most of my driving is from the bridge, but I may just buy a couple of them to put at the helm downstairs. I did read up on the "fuel squirt" count method, and that is kind of neat!

Thanks for your good info.
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Old 11-04-2013, 00:09   #6
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Re: Tachometer replacement for Perkins 4-236

I have a pair of 4-236s and when I first start the engines there is no tach or charging happening until I turn the key into the spring position which would on some boats be the start position. This one is push button switch start. When I turn the switch it suposedly gives the field coils a bump to start the charging. My inquiry about this unusual method of getting the alternator going and the tach showing was apparently done to prevent burning out diodes in the alternator. I have in the past used the oil pressure switch to connect and disconnect the field providing the same idea.
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Old 11-04-2013, 01:14   #7
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Re: Tachometer replacement for Perkins 4-236

Been using a Tiny tach for a few years now. Keep it below decks but very handy for the hours counter and much more precise than a mechanical unit for regulating tickover.
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Old 11-04-2013, 06:25   #8
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Re: Tachometer replacement for Perkins 4-236

I did order a couple of the diesel Tiny Tachs yesterday. They come standard with only 8' of RG274 coaxial cable, which would not be enough to reach from the engine to the bridge anyway. Although, I do not think it would be any particular problem to make up a couple of extender pieces of coax. They will lengthen the standard cable for $10, but for two of them that would be $20 extra and I can probably make up a couple for about $5 or so. More importantly, I can make them the exact length that I want them to be.

John
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