Tachometer on a Yanmar 3GM30FC with saildrive

[bigdogandy]

Agreed! Didn’t intend to discount the wisdom of the forum - I have learned a tremendous amount by reading here.

[wannacat]

Is the sender and wiring diagram the same[similar] for a 2GM20F with SD20 sail drive?
Not trying to hijack the thread but need the info please.

[MCOS]

Consider an alternative, Tiny Tach, a unit that has a sender which counts the pulses in the injector tubing by a unit which clamps over the pipe. No cutting of the tubing and can easily be removed. The pulse is sent through a wire which leads to a small digital read out. Simple two wire hook up, Cost about 100 to 150 - here's one listed on EBay

https://www.ebay.com/itm/Genuine-OEM...AAAOSwUhJgGwvS

[sailormed]

Before buying on EB, I would recommend you look at the TinyTach website. Last time I looked there they asked for injector line diameter. I do not see that option on EB.

[MCOS]

The kit that came with the Tiny Tach when I ordered it had a insert for small feed pipe 1/4 inch that you could leave out if you had 3/8

[NorthCoastJoe]

That is the right spot. If you thread the sender in until it touches the flywheel and back it off about half a turn you should have the right gap. I bought a tach that was universal and had to set a pointer on the back to a tooth range. My Yanmar 3gm30f flywheel was 92 tooth. It works well no problems.

[NorthCoastJoe]

The tach wiring is the same for the 1gm- 2gm -3gm and their variants.

[sinnerman]

Yes. This bolt looks like it covers the hole for the tachometer pulse sensor.

The engine flywheel has small "teeth" on it's outer diameter (OD). As the flywheel rotates, the teeth move past the sensor, and each tooth passing by creates an electrical "pulse" which is sent to the tachometer. The tachometer counts the pulses and bases its measurement against time to give you "RPM"

For example, if the flywheel has a total of 180 teeth, then each revolution of the engine will create 180 pulses. Therefore, one "RPM" would be 180 pulses in a one minute time interval...

You need to match the Yanmar tachometer to the flywheel. On the tachometer face there will be a "P=xxx" which indicates how many teeth the flywheel should have to be able to work with that tachometer.

(Example P=117 = a flywheel with 117 teeth...].

If you buy an off-the-shelf tachometer you will need to calibrate it by measuring the engine speed with an optical tachometer and adjusting the tachometer to match the engine speed.

Also as others have stated, if your alternator has a tachometer output, you can use this as for your tachometer input. Again, it would need to be calibrated.

[NorthCoastJoe]

I do not think there is a need to calibrate the tach unless you really need to know the exact RPM. Mine is off by about 100 RPM at WOT but who cares. I know that when it reads 3500 I am at 3600. Does it really matter if you know exactly, I would say not?
There is a fine adjustment on my tach but I felt it is splitting hairs.

[wannacat]

Thanks-North Coast Joe!!!

[01kiwijohn]

Later models have an alternator driven tach. Have a look and see if there's a small, extra, wire sticking out the side of it. Much easier installation than back at the flywheel.

[chasfgr]

Most Yanmar tachometers appear to work off the alternator.


Certainly all three of the YM and GMs I have owned did.

[RaymondR]

Take the plug out and have a look in there with a torch. If the threaded hole centre lines up with the teeth on the starter ring gear the threaded hole is most probably for the fitting of the variable reluctance tacho transducer Yanmar used on the 3GM series engines. The sensor works on the changes in the magnetic field as the steel teeth go past it.

[Differentroads]

Originally Posted by scaarup

Hi fellow sailors.

I have a Yanmar 3GM30FC engine with an SD20 saildrive. I have no tachometer but would like to install one. I have made some investigations and I would like to know if it is possible to replace the bolt (marked on the attached picture) with a sender unit (part no. 128170-91160)?

Thanks in advance.

That bolt is precisely where the rev counter sender is on my 3GM30F.