Tachometer

[1sailaway]

I just installed a used tach on my Islander Freeport 41. The old one was history. The new one will not register low (idle) rpm's but when I hit the throttle it jumps up there. My question is, is the problem with the sending unit or is there an adjustment on the meter. I have no experience with engines and cannot begin to tell you where the sender is located. Would it be better to replace it or attempt to repair? I hope someone out there can help.

Rene

[CSY Man]

Meh thinks most electric tachometers takes the input from the alternator.

Perhaps ya can clean and inspect the wires, or perhaps yer alternator is not "putting out" untill the RPM gets higher than idle?

[1sailaway]

Thanks for the input csy man, are you saying that the problem may not be in the sending unit? I have the factory alternator which I believe is a 45 amp. I was told I should get a larger one.

Rene

[CSY Man]

45 APM alternator?

Well, how big is yer boat and how much power do ya need to charge batteries and all that...?

I have a 33' boat with 150 Amp alternator, 3 stage charger, solar panels, big batteries and all that.

Can't get more than about 110 amp from a single belt, but I love my set-up.

Meh think ya should have at least a 75 amp alternator if ya have an inboard diesel and like to charge the batteries faster than now.

I got the PowerLine brand which is about half the price of Balmars and does the same job, no problems in 6 years of running.......

As far as the "sender unit" to yer tach, meh thinks it is only a couple of electrical wires, not really a "sender unit" as in oil temp or oil pressure.

[Alan Wheeler]

And just to add, check the back of the tacho for a switch that selects 4cyl or 6cyl. If there is one, it just sets the number of cycles the Alternator or what ever it is connected to, makes before it counts one. This could upset the idle range if not correct.

[delmarrey]

I'm assuming you have a diesel, and being so you probably have the magnetic pick up.
There are 4 kinds of tach's . One is mechanical that runs off of a cable like a speedometer.
Two, is the electrical which counts the time the coil sparks on gas engines (not likely yours).
Three is the impaluse type that runs off of the altenator and counts the cycles.
And four, is the mag. pick up type which counts the number of teeth on the flywheel. (most likely yours).
One is also made for outboards.

Look around the area where your flywheel starter gear would be. Most likely oppisite side from the starter. Chances are it'll be a solid gray or gray striped wire.
If so, then there is an adjustment for the sending unit. On mine it is: With the motor off, tighten it down until it touches then back off 1/2 turn and lock down.
Another thing, on the back of the tach there maybe a dial that adjust to the number of teeth of the flywheel. The tach has to match up to your motor. If there's no adjustment then it maybe incompatable to yours.
New modern Teleflex tach is around US$120 if you shop around. Last May I just replaced my old S&W that had rusted thru.

[1sailaway]

Ok, now I am really confused. I found the sending unit and there is nothing connected to it. I hooked up the new tach just like the old one was and I assume
instead of going to the sending unit it goes to the VR/alternator (im guessing). My guess is that the former owner replaced the original tach (mag type) with an electrical type. Does this make sense? Yes I do have a diesel, 100 hp Nissan SD-33 and believe it or not the 45 amp alternator is factory installed. Does'nt that seem to small?

[CSY Man]

Yes.

[delmarrey]

The real question is which tach do you have? The mag type will have two connectors for the mag pick up wires, an ign. connector, a ground/earth usually connected to the mounting bracket and possibly one for a light.

The electrical type will only have a one wire connector that connects to a separate + terminal on the back of the alternator, an ign. conn., the ground/earth and the possible light.

And yes a 45-amp alt. on a 100 hp motor does seem a bit light. Anything larger though the belt would need to wrap, at least, 120º around the pulley. That could be the reason for such a light alt. is not enough surface contact for the belt.

If your tach is driven off the alt. you may want to check the belt tension, that could be another possibility for erratic reading............_/)

[1sailaway]

Geronimo!! The used tach was defective. Thanks all for your inputs.