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  Sticking Teleflex RPM Gauge

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Author Topic:   Sticking Teleflex RPM Gauge
croatti posted 06-03-2007 09:03 PM ET (US)   Profile for croatti   Send Email to croatti  
I think I have a Teleflex Gauge which I believe is part number 1108470. (ink printed numbers on the side of the body) The other number is 1261. The gauge sticks when running the engine. I don't know if it is the gauge or the sender unit on the Mercruiser 350 inboard engine. When the needle sticks, sometimes I give it a tap with my knuckle and the needle goes up or down at random and most of the time I can get it to work.Because tapping the gauge works, I'm thinking that the gauge needs replacement but since these are costly items to replace, I would like to be sure. The boat is a 1987 Carver Mariner 32'. Since I have dual engines the right side works 90% of the time. But the other 10% it does the same thing as the Left Tach. Any help with this matter would be appreciated.

Marc

jimh posted 06-04-2007 09:11 AM ET (US)     Profile for jimh  Send Email to jimh     
Unless I have misunderstood your description, you are inquiry about an electrical tachometer. There is no electrical mechanism which I can think of which would cause the electrical signal being sent to the tachometer to "stick". The signal sent to an electrical tachometer is a signal of more or less constant amplitude but of varying frequency. The frequency of the signal is proportional to the engine speed. If you observe a reading on the tachometer which appears to be "stuck" yet the engine speed itself is changing, it is highly unlikely that the electrical signal being generated in the engine and sent to the tachometer is to blame.

In my experience it is far more likely that if an electrical meter indicator appears to stick, and it can be unstuck by tapping on the meter dial face, the problem is very likely to be a mechanical problem, not an electrical one.

Since you have twin engines and twin tachometers, you can perform a simple test to see where the source of the problem happens to be. I will describe it for you:

--with the engines stopped, locate the sender wires which feed each tachometer the electrical signal

--disconnect the sender wires and swap them between the two tachometers

--restart the engines and operate them in the normal fashion

--observe which tachometer displays the problem with sticking

Here is how to interpret the results:

If the problem of sticking moves from the original tachometer having the problem to the other tachometer which did not have the problem, then the source of the problem is in the sender circuit.

If the problem of sticking remains in the original tachometer having the problem, then the source of the problem is in this tachometer.

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