Yanmar engine revs used ???

[eianm]

I have read with interest a number of posts recently talking about running Yanmars at well over 3000rpm. I have a 1991 H42 with the 4JH2-TE. As mine has a lot of hours,and as i always thought diesels needed to run at much lower revs, I have not been running much above 2000rpm- I would be really interested to know what long term Yanmar users consider a "normal" running rev level- i.e. when you are not in any great hurry and then an upper limit to run at for maybe an hour or 2 if you were in a hurry??
In particular , I would love to hear from other series 1 (1990>1996) H42 owners with the same engine to know what their experiences are please. I am currently running the original factory 2 blade but will change to a 3 blade varioprop in 2 weeks time when I do the annual slip.
Eian

 

[Steve Dion]

Eian:

Here is a website that you may want to browse. The recommended RPM for cruising is 70-80% of the max rated RPM. If your engine was rated at 3600 it would mean that you should run the engine at 2900.

http://www.yanmarhelp.com/index.htm

 

[kloudie1]

Eianm, the older Yanmar tachometers are notoriously inaccurate, so ya need to check with an accurate handheld tachometer before making big changes in the way that you run the engine. I found mine to be over 20% off.. reading lower than the "real" rpm

 

[BBC16385]

We have the 1997 Hunter Passage 42 with the same engine as you [I think]. It is a turbo with about 62 hp. Our max RPM under load is 3600. We motor full ahead at between 2900 to 3100 depending on conditions. We motor at "half speed" at about 2400 to 2600. The difference in speed from full ahead to half speed is 7.5 kts to 6.5. We do more half speed motoring than full ahead and see no ill effects, but do see significant fuel savings. We use a 17 inch folding two blade prop. We add Lubricity and Cetane and StarTron to the fuel. http://mystarbrite.com/startron/

 

[Ivan]

Whatever you do, all marine diesels need to be run at full throttle, or nearly so, for at least one hour every at least 10 hours of operation or the cylinders will glaze up and you will stare at big expenses. 2000 rpm is way too low for cruising, and if you do that most of the time you are virtually guaranteeing trouble.

 

[waternwaves]

to get to 80% power out of most yanmars, you have to go greater than 80% of max speed, especially id you are running a 2 blade prop,

Diesel mechanics I know all recommend 80% power loading, and unloaded engine at 80% speed is not helping .

if I were to cruise at 80% rpms it would be at 2800, however I would only be loading the engine 50% of the rated horsepower, (20 hp, well below what is recommended.)

A yanmar 4jhe marine diesel I know of runs 3400 rpm continuous on a generator turning a motor at 3600 rpm, and went almost 8,000 hours of operation before a rebuild, but that engine was protected from salt in a building.

In the case of my engine the 4jhe and a 2 blade, I need 3300 rpm to get to 80% power, (prop efficiency is worst at low speed) and most of our cruising is done at full speed or sailing. for the last 400 hours (maybe 5K on the engine) oil changes every 200 engine hours, she burns about a quart every 150 hours, is a little smoky (espeicially to start), and a little over a gallon 1/4 - gallon 1/2 an hour of diesel at cruise

Unloaded and low speed operation kills yanmar diesels

IF your tach is off, I would first check your alternator/charging circuit, any drop in proper alternator output causes the tach to read low. With a proper alt circuit, I have found maybe one tach circuit more than 50 rpm off in 30 years, and that is from looking at hundreds of tachs.

 

[Dan Johnson]

Waternwaves...

Earlier and smaller Yanmars used a magnetic pickup at the flywheel teeth as the sensor for the tach, not the alternator. Voltage is immaterial with this setup. Using a laser tach, I (and others) have indeed found that the RPM at the tach head can be as much as 20% off the actual rotational RPM at the engine's crankshaft pulley.

 

[kloudie1]

From the manual

The original tach for that engine used a pickup as Dan noted..
http://sagaforumet.com/yanmar-manual/4JHE/kapittel_9.pdf

 

[waternwaves]

Dan,

the problem is by far and large the voltage supplied to the tach, as alternator output drops, poor voltage regulation causes the amplifier circuit in the tach reading to decreases in magnitude and results in RPM reading low.

I did not imply the tach has a pickup "on the alternator" The mag signal to the tach changes very very little over the years, (magnets age slowly) The "bat" connection to the tach is critical, changes in supply voltage (from an alternator), RF transmitters, and other heavy electrical loads mistakenly put on the circuit, on the boat can affect the tach reading.

The Tach "signal" from the transducer is always locked to the rotational speed of the engine. There are only a fixed number of magnets on the engine. The problem comes with the amplifier (Tach).

 

[kloudie1]

The tach pick-up "counts" the 127 teeth of the ring gear as they pass and divides by time.. No magnets involved.. Tach operates from 10 through 15 volts.. The problem with these older ones is that the mechanics in the tach get sticky and sometimes the connections on the pick-up coil get bad and the signal is partly interrupted or gets weak.. Click on the link in my post and click on "Tachometer" and the specifications for that tachometer on that engine are there..
Many newer diesel tachs use the three phase signal from an alternator to make it read and yes, those can give strange readings when the alternator drops output amperes as the batteries come up to charge..
This dead horse has been kicked about several times on the forum..

 

[waternwaves]

I believe you will find the transducer is a hall effect sensor. (a voltage varying magnetic sensor)

The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current.

sorry, my comment on "fixed number of magnets" is misleading, and would have been more accurate as a fixed number of teeth, it is the magnetic properties of the tooth that vary the signals back to the tach, and I should not have simplified.

I tried to simplify language for the non technicals, the hall effect is a change an observed relationship in which magnetic field changes and corresponding voltage observed. We could go on to describe this change as a coupled magnetic circuit which changes dielectric of the core of a transformer by the absence or presence of a tooth in the flywheel by the change in magnetic field for the missing tooth. (but I think most would have fallen asleep three sentances back.

It is still a magnetic effect ("sans magnets) varying to generate the voltage signal amplified in the tach control head.

The gist is the Tach control head (meter)kis a very sensitive circuit, and is sensitive to drops in voltage and one can easily demonstrate the results.

The critical device is the Tach, and the critical element is normally the Supply reference voltage.

 

[kloudie1]

The real issue is that the tach on these older Yanmars aren't accurate nor repeatable sometimes.. My suggestion was that he use a hand held, either mechanical or an optical interface to get the real RPM before making a decision ..

 

[Dan Johnson]

Waternwaves...

Point well taken on the voltage effect on the strenght of the signal being received.

Many of the problems with the tach reading "funny" is that the connections need to be cleaned periodically, especially down at the pick-up and the mid-point connector. Once all these connections have been cleaned and crimped tighter, the problems seem to go away. Doing so insures that there is no corrosion resistance at the connectors causing a voltage drop.

Cleaning all the connections at the back of the panel also makes a big difference. Also, putting sealant tape on the back side of the panel around the edges will practically eliminate water intrusion which leads to the corrosion.

 

[zds]

This may be a dumb question with an obvious answer, but a handheld optical tach (for example) could just be shot at the crankshaft where it exits the front of the engine to turn the belts... right?

I specifically asking in the case of my 3gmf, but this is true for all engines... right?

 

[kloudie1]

Yes.. It helps to have a thin white stripe (tape or "white out" so the optics have an easier time of counting.. but yeah.. Ya aim it at the crank pulley push a button, and it gives ya a number.. Most of em can be checked for calibration by aiming at a standard fluorescent light bulb (magnetic ballast).. they will read 7200 RPM ..

 

[Roger Long]

FWIW I've never had any problems with the tach on my 2QM20. The manual says the engine is governed for 2800 and that's what it's always read at WOT. RPM has never seemed to drift or vary except for the tack dropping momentarily back to zero when I did have a loose connection on the sender unit.

I just assumed that it was counting flywheel teeth since we're all so used to digital circuits. After reading this thread and looking at it during my recent engine room wiring overhaul, I realized that, of course, there is no way it could be with 1970's technology and two wires.

I wish I had checked my RPM independently before having my prop re-pitched. However, since there is no sign of black smoke at WOT and the RPM is exactly what it is supposed to be, I suspect that I'm OK.