Tachometer Question Yanmar 20QM20

[pelicanj45]

I have a ’81 Hunter 36ft. It’s equipped with a Yanmar 20QM20.
I’ve been the happy owned for 25 years and have never had a tachometer for it.
I have the factory dash with a starter key and a buzzer. I assume that’s basic , basic, for Yanmar. There exists one covered hole in the dash which I again assume is for a tachometer. I’d like to put a tachometer there.
1. I’m looking for a tech. If anyone knows where to look.
2. Not sure what to look for too get a reading from the motor.
There are several dead wire leads coming from the motor, which I assume are factory wiring harness. There are no spare wires lingering around, just empty harness connectors.
For 25 years I’ve run the boat just by sound. There is a lot of throttle not being used. I’ve ramped the motor up when taking Huron waves on the bow and it’s never faltered. I think there’s some RPM’s that I’ve never used.
Any comments?

JC

 

[rardiH36]

Hi fellow Cherubini Hunter 36 Owner:

I'll be at my boat tomorrow and will take and post close-up pictures of the Yanmar 2QM20 manual pages that describe the operation/wiring of the factory installed tachometer. My recollection is that the engine rpm sensor is magnetic and is thread mounted just outside the circumference of the engine flywheel that the starter engages into. The sensor circuit then converts frequency of the flywheel starter gear notches passing by into rpm info for the gauge on the panel. Not sure if this will help vs. doing an after market alternative. But something in the info might be useful for you.

 

[pelicanj45]

Rardi,
my guess is that with all the wiring harness with dead end connectors that Yanmar provided for the tach and Hunter didn't spring for the tach.
But thanks for taking a look. As they say pic's worth a thousand words.
JC

 

[kloudie1]

Tachometer

JC, one of the forum guys, Ralph Johnstone, found this VDO which is good for all inputs.. If you have a flywheel sensor, it will work with that .. if you don't, it should work with your alternator .. It has a bunch of scaling options to make it OK for lots of engines..
http://www.egauges.com/vdo_ind.asp?Type=Tachometer&Series=Vision&PN=333-163
I don't know if E-gauges is still the low cost vendor ..
I looked at the manual for the 2QM and it shows a flywheel sensor but don't know if you actually have one on the engine.. The harness wires are colored Green and White .. The green connects to a blue in the harness then comes out at the panel as green again. The white wire connects to an orange wire in the harness, then back to white at the panel.
The ring gear has 126 teeth, according to the manual.
rardi's picture should let ya decide whether you have the sensor or not.

 

[rardiH36]

Rardi,
my guess is that with all the wiring harness with dead end connectors that Yanmar provided for the tach and Hunter didn't spring for the tach.
But thanks for taking a look. As they say pic's worth a thousand words.
JC

Thanks for acknowledging. I'll post the pics tomorrow evening. Just as a note, my 2QM20 is fitted with the tach.** So I'll see if I can get my camera into the engine compartment well enough to photo the sensor and the connectors. If I had the famous Cherubini H36cockpit sole engine access cover removed, taking the pics would be easy, but I don't want to remove it only for this task.

** The tach is a great feature. Particularly when I ask guests (or my wife) to take the helm while I go forward to drop the sails or when tidying up when motoring in or out. The 2QM20 has certain rpm ranges that are much smoother than others with vibration. (1400, 1600 and 2200 rpm for my boat). So I can call out the rpms I want them to motor at!

rardi

 

[pelicanj45]

rardi,
Re: famous Cherubini H36cockpit sole engine access cover.
I wont go into detail but I managed to crack the Yanmar block.
I've pulled that motor out three times now. Three trys to weld. Now I have a pin hole leak. A little JB Weld and a can of Bars leak problem solved!

I have all of the wires marked and differen bolts go into different baggies.
From my slip to the haul-out, wrecker boom to lift it out and on to a skid, 2 hours tops. Closest marine service to me is twenty-five miles by water. Generally you're your own best mechanic.
I've seen guys take motors thru the companion way. Nice to have that cockpit opening.

I told the guy with the wrecker that I was gonna put a string on it and call it a Yo-Yo.
JC

 

[rardiH36]

JC: Glad the JB weld epoxy is holding. But details please. Ideas why your block cracked?

My 1980 built engine is still in one piece. Looks pristine for its age and performs great. I haven't seen any indication of impending block or head or exhaust manifold failure. Maybe PO's always looked after the engine well (as I am trying to do now)!

But I'm interested in your problem because of the modification by Hunter from a 2QM20H (the 140F thermostat sea water cooled version) to an anti-freeze cooled version by the addition of a bulkhead mounted external heat exchanger. I probably came close to doing damage to my engine a few years ago when because of guests arriving and also while not being at my home slip, my normal routine was disrupted. The raw water sea cock was not opened. 10 minutes after the engine was started, the external heat exchanger's pressure cap vented which fortunately we noticed immediately. The boat was fitted with only a 5-7 lbs low pressure cap thank the lucky stars so damage temps had not been reached. The engine temp alarm did not sound. Investigating later, I found that the temp alarm sensor installed by a PO (or Hunter?) was a 190F type which did not match the 140F thermostat which is the only physically sized thermostat that can fit in the 2QM20H thermostat housing. That meant that the engine temp had to reach 50F more than normal before the alarm! I promptly ordered/installed a 140F sensor switch. I now feel more secure, but 140F switch gives me problems sometimes during the summer if I am motoring at 80% rpm then stop the engine for say 5-15 minutes. Upon restart the temp alarm goes off. Then stops after several minutes of operation. I also have a engine temp gauge. I can look and see that the engine has not overheated. (Well maybe 145F instead of the normal 135-140F.) I think what is happening is that when I stop the engine after prolonged motoring,the latent high heat along the cylinder walls eventually warms up the entire block to over the 140F alarm switch threshold. The alarm sounds until the restart circulation through the heat exchanger eventually cools down the anti-freeze after a few minutes.

 

[pelicanj45]

rardi,
As I said before, you’re either your own best mechanic or your worst mechanic. About three years ago I became my own worst mechanic.
The story:
It started with the heat exchanger pump shaft began to leaking. I re-hosed the motor so that I could by-pass the exchanger pump until I could get a replacement. It was end of summer before I got the replacement pump. So I waited until the boat was hauled for the winter before replacing the pump. I winterized the boat including the heat exchanger, just didn’t drain the block of fresh water. DUMB!!!
Come spring and first sail out, I discovered water on the cabin sole. *@&%%!!
I’m in AuGres MI. Google it. It’s in the middle of no-where.
Pulled the motor with the use of the local wrecker and took the motor to a guy with a welder in his shed, in Standish Mi. another middle of no-where. He welded it and I put the motor back in the boat. Motor leaked, used the boat as a summer cottage that year. Fall came and I called the wrecker out again. Yep, pulled that motor again. This time I took the motor down state where welders know how to weld cast. “ If it leaks, bring it back”, from the welders lips to gods ear. Yep, it leaked. One more year passes. Motor out, motor in. Now it’s JB Weld and Bars Leak. Should’a done that three years ago.

Last note, AuGres is a great place to sail out of. Nice bay for day sailing or cruise north or east 25 miles for week-ends cruises. Mi. is a great place for costal sailing. State run harbor about every 25 miles.
JC

 

[rardiH36]

JC: Appreciate the description and story. Common theme for all of us and just about everything, on land also; unintended consequences. One variation from the normal snowballs into a later issue. Pending pump repair caused fresh H2O in the engine instead of anti-freeze that I presume you would have normally left in the engine over the winter. Followed your normal winterizing routine. Not a problem in San Francisco.

Pictures of the tach pages and engine this evening.

rardi

 

[rardiH36]

JC:

Attached are pic's of the 2QM20 manual pertaining to the tach system/circuits. Also, a picture of the actual sensor on my engine showing the orange and blue wires that are specified in the manual. Please excuse the blue ink writing on 2325.jpg which documents my "forgot to open the sea water seacock" alarm circuit that I added to my boat after a scare when I left the berth without the seacock open. Note on the bottom of 1024.jpg, that Yanmar states that the R terminal of the alternator can also be used for a tach. Maybe this output will enable a generic after-market tach gauge? You will have to do your own research on this. Hope something in this will help.

rardi

 

[pelicanj45]

Tachometer question w/pic

rardi,
thanks for the info and pic. Looks like I have the wiring but on pick-up screwed in the flywheel housing.

JC