Adapting an automobile tachometer

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Chanquete

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Hy
The tachometer on the motor panel of my volvo 2030 engine dont return to zero after switching out the motor.
If the trouble goes worser I am thinkin in changing the tachometer.
Here in southamerica we also suffer with the extremely high prices os genuine volvo spare parts.
A friend with a similar volvo installed an automobile tachometer.
The tachometer works but the readings do not correspond to the real rpm.
Any idea of how to adapt such a tacho?
Thanks in advance

Saludos
 
Chanquete said:
The tachometer on the motor panel of my volvo 2030 engine dont return to zero after switching out the motor.
Click to expand...

1) Is that a problem?
2) On our engine (Beta, not Volvo) the tachometer takes a few moments to return to zero. If we switch the engine off as soon as it stops, the tachometer stays above zero until next time we turn the engine on. However, if we leave the engine switched on and wait for perhaps 5 to 10 seconds the tachometer returns to zero and then we turn the engine off.

If you do need to replace your tachometer try looking on Google for a product called TinyTach (or something similar). I'm sure there'll be someone along here soon to give more detailed advice/name/address about it.
 
An old style auto tacho will be operated off the electrical impulse from the ignition system . Usually the points or connection to the primary of the coil. Now days if it is a diesel of course I don't know but could be driven from the auxuliary (w) terminal of the alternator. All these electronic tachos give an indication which depends on the number of pulses per revolution of the engine. So a 4cyl car tacho might get 2 pulses per revolution from the points. However presuming your boat has an alternator driven tacho then the pulses more like half cycles of AC will be 6 per revolution of the alternator which may be geared up by pulley sizes to possibly around 10 per rev.
My point is there are so many variables involved that you will need an electronic tacho which can be adjusted for accuracy depending on the source of pulses. I don't know if auto tachos are adjustable. Possibly not being made for large number of cars of one type. So unless you have an electronic bent you might be better off going for one of the after market tachos "Tiny Tach' comes to mind.
good luck olewill
 
Chanquete said:
Hy
The tachometer on the motor panel of my volvo 2030 engine dont return to zero after switching out the motor.
If the trouble goes worser I am thinkin in changing the tachometer.
.Saludos
Click to expand...
That doesn't indicate a fault. AFAIK, it's a feature of a display driven by a stepper-motor, as in many tachos.
The reading stays at the rpm at the moment of switching off the power to the instrument.
Can't help with the calibtation.
 
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