Rev Counter problem

[reedham]

I have just got a day boat about 20- 30 years old with a Nanni 2.60 engine. The rev counter does not work there is a - supply & + via the ignition which are ok. There is a thin coax cable to an alloy clamp on one of the injectors which appears to be a sensor of some sort. Any ideas what the problem might be?

 

[JasB]

After 20 - 30 years you are probably better off stripping the old wiring and starting again, my Snapdragon is about 30-ish and the wiring has been modified by various owners and I have found most of the wires to be redundant. To try and decypher the old emergency repairs and the bodge jobs can be a nightmare.

 

[reedham]

I agree it has been a long job sorting out previous bodges, the rev counter is really the last one for now. It is probably the guage itself but I would like to know how the sender works.

 

[srp]

Sounds like you've got a Tiny Tach - http://www.tinytach.com/tinytach/diesel.php - they have an internal battery which is supposed to last about 5 years (it stores the 'hours run' and 'time to service' data) but even if it's dead it should still display the engine revs. They're imported by Richard Dunn who lives in East Grinstead, Sussex, who was very helpful when I bought one. His email address is itco <at> btopenworld.com

 

[reedham]

It is not as sophisticated as the Tiny Tach, just a simple round RPM x 100 instrument with no makers name.

 

[Lakesailor]

Did it ever work. Has someone tried to make an impulse sensor work with any ordinary tacho.
This forum discuses the different types of tacho
http://www.boatdesign.net/forums/showthread.php?t=14844

 

[wiggy]

Bit of a hijack here, hope you dont mind, i have 1GM10 with non yanmar alternator with tacho conection on rear. Will any tacho for diesel such as this about 2/3rds down page do the job?

 

[Lakesailor]

I'm no expert, but as far as I can tell the alternator driven type are not very accurate. It would depend on having the same size drive pulley as the correct one. Although it seems tachos for alternator sensors have adjustment so you can set it for your own set-up.
However the injector impulse one mentioned by srp.... would sound like a much better bet, to my mind.

 

[reedham]

Thanks Lake Sailor, at least I now know that the sensor should be on the injector ( but I don't understand how it works with bn moving parts). If it has no moving parts does it mean there is nothing to go wrong and that I can eliminate it from the equation?