Yanmar 2QM20 Tacho Problem - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 10-08-2013
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Yanmar 2QM20 Tacho Problem

On my Yanmar 2QM20 the tacho needle swings wildly between 0 and 5000 rpm while the motor remains at constant revs-The pickup is like a little generator and is driven by an internally driven geared shaft, from the pickup the wiring (3 wires) goes to the tacho.Does any kind soul know if it is possible to test the pickup and what does one look for.The manual hardly mentions this type of pickup but instead refers to a sensor that picks up a signal from ring gear while mine is direct drive.Also how does one test the tacho itself.Thanks in advance.
Chris
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New Zealand
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Old 10-09-2013
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Re: Yanmar 2QM20 Tacho Problem

The 2QM15s and 2QM20s I've seen have all had magnetic pickups. Is it possible the teeth are warn and not engaging on the gear drive consistently? Could you post photos?
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Old 10-10-2013
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Re: Yanmar 2QM20 Tacho Problem

Thanks Farcry--The sender on mine has a fork that goes into a slot on the drive,definately mechanical.It is strange as workshop manual does not show this.-the sender does have a double nut system on it,maybe I should separate these and see whats hidden.I connected up the tacho head unit today and everytime I turned on the ignition switch the needle went right round to max then back to zero again-does this give anyone a clue as to what maybe is wrong,I am suspecting the head unit not the sender.-Thanks.

Chris
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Old 10-19-2013
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Re: Yanmar 2QM20 Tacho Problem

Sorry folks but I am still stuck on my tacho problem--On page 73 of my parts book under Instrument Panel the type of sender unit I have on my 2QM20 is item 17-33--This sender and tach seem to have been an optional extra with this motor.It is located just to the left of the water pump and it is gear driven-it is not the sender that is flywheel pickup driven.It has 3 wires running from it black,orange and blue which go to the tach head unit where a fourth wire,red and black, joins it for power supply.When I turn on the ignition key the needle goes round to maximum and stays there,almost like there is a dead short in the head unit.Can any kind soul throw some light on this problem,I would dearly like to obtain a circuit diagram of the head unit if possible as I believe this is where the problem may be but I don't know what I am looking for.I have Googled everything I can on Yanmar tachs but have had no luck.If this cannot be fixed is there another type of tach that would work with this motor and how would it be driven.Thanks in advance.
Chris
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Old 10-19-2013
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Re: Yanmar 2QM20 Tacho Problem

Can't help with your existing system. To answer your other question, I'm fairly confident a magnetic pick up system could be installed on your motor. I did that just last year on a 2GM. It took more time to drill a hole for the gauge than to do anything else. Depending on your alternator you might be able to drive a tach off of that as well. Most newer Yanmars use the alternator.
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Old 10-19-2013
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Re: Yanmar 2QM20 Tacho Problem

My 2QM15 didn't have a tach when I bought it and didn't for many years until I bought a Tiny Tach. 95 bucks and works like a champ. Sender clamps to FI piping and counts pulses of fuel.

Design Technology, Inc., Home of the Tiny-Tach - Diesel Tiny-Tach Tachometer
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