Yanmar Engine revs to 4000 RPM

[BlueChicago]

I purchased a new Gori 2 blade folding propeller this past spring. Along with other necessary specifications, I provided the distributor with my engine model (Yanmar 3JH5E), and transmission (KM35P @ a 2.36 ratio). The distributor indicated the diameter and pitch needed, and I ordered it.

I had never pushed the engine with the new prop until later in the season when heading back for winter haulout. At that point, I noticed that I could push the engine to 4000 RPM (as displayed on the tach).

The engine is relatively new, and currently has about 200 hours on it.

I'm embarrassed to say that I can't remember what the maximum engine speed was when the old prop was still on the boat. I want to say about 3000 at full throttle (I replaced it because the original, pitted, cracked prop would have cost more than half that of a new one - and no guarantees)

Assuming that the tach is accurate, my questions are:

Should I be concerned about revving the engine this high?
Do I have the incorrect prop, or could the issue be related to something else?



Thanks


-BC

[NoTies]

I suspect you need to have your rev counter calibration checked before you go any further.

[BlueChicago]

Originally Posted by NoTies

I suspect you need to have your rev counter calibration checked before you go any further.

Can that be done while the boat is out of the water?

[NoTies]

The engine needs to be running at cruising revs to calibrate accurately. If you can provide cooling water I guess it would be OK.

[donradcliffe]

The engine is rated at 3000 rpm max, and the governor should limit it to that.

[Seadoc777]

Check You Tube under the subject Run Away Diesel Engine.

[Scubaseas]

Engine rpm can be check with boat in water. Engine should run at 3000 rpm max. Either your tach is not reading right (probable) or you are way under pitched.

[Cpt Pat]

As an aside, diesel engine runaway is what caused the initial explosions leading to the Deepwater Horizon disaster. A gas "blowout" caused the platform to be enveloped in methane gas. The diesel AC generators aspirated the gas and used it as fuel. Even with the diesel fuel cutoff by the engine speed regulators, the engines continued to run on the methane without fuel-regulated speed control. In a situation like that, the only way to stop a diesel engine is to cut off its intake air. If you watch the movie, you can see this catastrophic process progressing, but it is never explained. You can view that 1:50 into this clip:

https://www.youtube.com/watch?v=-4YWhct3ty0

Note: the output voltage from a generator is proportional to its rotational speed. That's why the lights exploded.


I sometimes wonder if vessels have been lost at sea because of either propane leaks reaching the engine, or outgassing of methane from the bottom; leading to "dynamic disassembly" of a running diesel on board. It's too bad the engine shutdown on many diesel-powered boats shuts off the fuel flow instead of the intake air. At least that would give the crew some chance of manually shutting down a runaway diesel engine. This is one case where a gasoline engine can be safer: you can shut it down simply by turning off the ignition.


The Deeepwater Horizon accident was especially inexcusable because the runaway would have been so easy to detect and prevent. Diesel engines driving an AC generator run at one constant RPM, and anything over that value could have activated an intake air cutoff. It's not like methane-aspiration was unforeseeable on an oil platform.


There's more here: https://www.aiche.org/ccps/conferenc...away-explosion

[mtarcher]

I noticed my new Yanmar engine did the same, with using the old prop. I found out the prop is somewhat undersized, but the main issue for the apparent engine over speed was due to the pulse setting on the B20 panel being incorrect. The Tahoe was actually displaying almost 10 percent higher than actual

[01kiwijohn]

Let's not get too hasty here.
First, check the high idle rpm, rent or borrow a photo tachometer if you doubt the one on the boat. Some of these engines have a spec of 3900 to 4000 rpm.
At full throttle, running in calm seas, with a clean bottom, the max rpm should be just a little north of 90% of that high idle speed. If much above, prop is to small or not pitched enough. If much below 80% of hi idle speed, prop is pitched too much.
At the speed you say, it seems like it is above that 90% level so my not be pitched aggressively enough.

[Malfoi]

Hi. I want to speak with you privately donradcliffe, please. How can I do this?

[01kiwijohn]

Just call 253three555716

[Scubaseas]

OP: Should I be concerned about revving the engine this high?


Yes


OP:Can that be done while the boat is out of the water?



Yes, Either supply water for salt inlet pump or take the impeller out. You can verify tach operation long before the fresh water cooling system will get hot enough to worry about. The exhaust won't heat up that fast either. Just don't run it more than about 2 minutes tops. Should take about 30 seconds to comapre your tach to an external (usually optical) one.

[Malfoi]

Is this donradcliffe number? I need donradcliffe user contact data. I am sorry.

[BlueChicago]

Originally Posted by mtarcher

I noticed my new Yanmar engine did the same, with using the old prop. I found out the prop is somewhat undersized, but the main issue for the apparent engine over speed was due to the pulse setting on the B20 panel being incorrect. The Tahoe was actually displaying almost 10 percent higher than actual

mtarcher,

Looking at the Operation Manual, it appears that the speed pulse value, for the panel that I have (C30) should be set for P10.29. Problem is that this is not yet clear to me what this value represents, and if this is the default for the panel or for the engine series.


I will check the setting, I am assuming that I can check these values without starting the engine.


I am really hoping that it is the speed pulse setting and not the prop. Unfortunately, I'm not finding much information outside of the Operation Manual regarding the speed pulse settings.


Thanks


-BC