Rough running Yanmar GM10 on the gear on high revs

[slawosz]

Hi,
I have issue with my Yanmar GM10. When on idle, its all good, the problem is with running on gear. The engine is running rough and erratic, vibrates (not too much), and there is black smoke.
Water pump is new, filters and oil changed. New waterpump. All I could check I think is the elbow but that one I checked in 2022 and it was new. Although from that time engine did around 150 hours - not sure how much elbow can take?
I notice that propeller (folding) is bit fauled with weed (boat on the deep water mooring), but I would expect it to clean by itself when engine starts. Might try to clean it though.
Oh, and engine has no problem with starting...
I wonder if someone experienced something similar?

 

[Tranona]

Sound like classic overloading behaviour from dirty propeller - unlikely to be self cleaning. When you have so little power as with a 1GM does not take much fouling to overload.

 

[garymalmgren]

When you say new filters, you do mean fuel filter don't you.
Your problem will likely be at the prop end as Tranoma has suggested or at the engine end.
At the engine end it could be fuel: not enough (blocked filter) or contaminated fuel.
How clean is your fuel tank?

gary

 

[bignick]

As @Tranona says, try cleaning the prop first,
A heavily fouled prop increases torque which usually results in black smoke.

 

[slawosz]

When you say new filters, you do mean fuel filter don't you.
How clean is your fuel tank?

gary

Yes, both fuel filters. I squeaky-cleaned my tank last year, and after that I am adding lot of anti-bug fluid, so its unlikely its a fuel.

 

[Sailing steve]

As @Tranona says, try cleaning the prop first,
A heavily fouled prop increases torque which usually results in black smoke.

A heavily fouled prop reduces the torque loading presented to the engine not increases it.

In the same way a car tyre can't grip an icy road and transfer engine torque to drive the car along a badly fouled prop loses hydrodynamic efficiency and can't efficiently transfer engine torque to the water surrounding it to drive the boat along.

Just like a car tyre on ice you may be able to make some progress at low engine speeds but open the throttle up and all you'll get is cavitation which is the boaty equivalent of wheelspin.

The OP should look for himself of course and maybe first of all check his prop easily turns by hand and if it does then see that his hull is smooth and clean. If there's increased drag from a fouled hull then that will compromise the engines ability to match the propellor RPM to the reduced achievable hull speed and most noticeability at higher power settings that will cause over fuelling and black smoke.

Another thing to attend too is engine breathing. if the air filter or exhaust elbow is partially blocked or valve clearances are incorrect then that will compromise airflow through the engine and again that will result in over fuelling leading to black soot and a smoky exhaust.

A worn injector will increase the amount of fuel injected on each combustion stroke too and and the effect of that is most noticeable at wide open throttle settings as the carbon molecules in the fuel can't find enough oxygen molecules to combine with so they're ejected as partially burnt carbon instead - hence the soot and smoke

 

[B27]

A heavily fouled prop reduces the torque loading presented to the engine not increases it.
...

Wrong!
A clean prop slices through the water with not much drag.
A dirty prop has lots of drag.

 

[Rappey]

A heavily fouled prop reduces the torque loading presented to the engine not increases it.

If i understand you correctly then i disagree. Recently i tested a 30hp diesel engine flat out tied to a pontoon and it struggled a little to achieve 2000 rpm . The load was too much for it.
Turned out the prop was fully encrusted in barnacles . After cleaning the prop and hull the engine instantly went to 3000 while moving.
Will have to tie to the pontoon again and see what max rpm it can do stationary.
You also suggested a badly fouled hull would load the engine. Im not sure about that. Ive moved fouled 26ft boats ( in the harbour when calm) with a dingy and tohatsu 3.5 2t. The engine sounds exactly the same full throttle whether pushing a small dingy or 4 ton fouled boat.

 

[B27]

If i understand you correctly then i disagree. Recently i tested a 30hp diesel engine flat out tied to a pontoon and it struggled a little to achieve 2000 rpm . The load was too much for it.
Turned out the prop was fully encrusted in barnacles . After cleaning the prop and hull the engine instantly went to 3000 while moving.
Will have to tie to the pontoon again and see what max rpm it can do stationary.
You also suggested a badly fouled hull would load the engine. Im not sure about that. Ive moved fouled 26ft boats ( in the harbour when calm) with a dingy and tohatsu 3.5 2t. The engine sounds exactly the same full throttle whether pushing a small dingy or 4 ton fouled boat.

A badly fouled hull can be an awful lot of drag.
Comparison between revs on a moving boat and a 'bollard pull' can be extremely flawed.
It can take a lot more torque to get the same RPM in a bollard pull compared to a moving boat.

 

[slawosz]

A heavily fouled prop reduces the torque loading presented to the engine not increases it.

In the same way a car tyre can't grip an icy road and transfer engine torque to drive the car along a badly fouled prop loses hydrodynamic efficiency and can't efficiently transfer engine torque to the water surrounding it to drive the boat along.

Just like a car tyre on ice you may be able to make some progress at low engine speeds but open the throttle up and all you'll get is cavitation which is the boaty equivalent of wheelspin.

The OP should look for himself of course and maybe first of all check his prop easily turns by hand and if it does then see that his hull is smooth and clean. If there's increased drag from a fouled hull then that will compromise the engines ability to match the propellor RPM to the reduced achievable hull speed and most noticeability at higher power settings that will cause over fuelling and black smoke.

Another thing to attend too is engine breathing. if the air filter or exhaust elbow is partially blocked or valve clearances are incorrect then that will compromise airflow through the engine and again that will result in over fuelling leading to black soot and a smoky exhaust.

A worn injector will increase the amount of fuel injected on each combustion stroke too and and the effect of that is most noticeable at wide open throttle settings as the carbon molecules in the fuel can't find enough oxygen molecules to combine with so they're ejected as partially burnt carbon instead - hence the soot and smoke

But arent some of those sympthoms (elbow blocked, spray pattern and clearances) would also happen on full speed idle?

 

[Sailing steve]

Wrong!
A clean prop slices through the water with not much drag.
A dirty prop has lots of drag.

Consider the physics.

It's primarily the energy required to displace maybe several tons of water as well as surface friction between the moving hull and water its in contact which causes drag and not the rotation of the propellor.

A clean prop will efficiently transfer the torque from the engine to the water which means the propeller will then be able to overcome the drag from the hull and push the boat along. When a prop is clean and correctly matched to the hull it will grip the water as the designer intended and when that happens the drag of the hull is the load presented to the engine via the prop.

When a prop is fouled it can't grip the water efficiently transfer the engine torque to the water so rather being able to overcome the drag presented by the hull and push it along it will just spin uselessly in the same way as a car tyre spinning on ice does. When that happens the only load presented to the engine is the resistance of rotating whatever is fouling the prop through the water its immersed in.

So instead of the propellor being able to deliver the torque the engine is developing and effectively push the hull through the water it'll just sit there revving it's cohones off instead, and you can demonstrate this anytime by wrapping a big handful of weed, a bundle of plastic bags or a few meters of fishing net round your prop.

Then come back and tell me I'm wrong.

 

[Sailing steve]

But arent some of those sympthoms (elbow blocked, spray pattern and clearances) would also happen on full speed idle?

Flat out in neutral the engine is not under any significant load and unless there's a major fault you'd expect it to be able to achieve the RPM the throttle setting is calling for which is the critical point.

When its under load any number of issues including poor injector spray pattern, reduced pop pressure or timing, incorrect valve clearances, reduced airflow from a partially blocked air filter or exhaust elbow or excess drag through a badly fouled hull or excess friction from a misaligned prop will become apparent and prevent the engine achieving the RPM the throttle setting is calling for.

If nothing else is wrong of course, when the engine can reach the RPM the throttle setting is calling for the air/fuel ratio will be correct, but when it can't reach that RPM or there's something else amis the a/f ratio won't be correct.

The 1GM10 is unthrottled and draws the same amount of air into the combustion chamber on each stroke regardless of engine speed or throttle setting. The power it develops is controlled by throttle setting and the amount of fuel subsequently injected on each stroke instead.

If for whatever reason the engine can't achieve the RPM the throttle setting is calling for then there will more fuel injected than there is oxygen available for efficient combustion - effectively it's running too rich - hence the soot and smoke.

Same too rich principle applies to incorrect valve clearances or a partially blocked air filter or exhaust elbow only here it's the other way round. The correct amount of fuel for the RPM might be delivered but there's not enough air getting in to the combustion chamber to burn it efficiently

 

[B27]

Consider the physics.
....

When a prop is fouled it can't grip the water efficiently transfer the engine torque to the water so rather being able to overcome the drag presented by the hull and push it along it will just spin uselessly in the same way as a car tyre spinning on ice does. When that happens the only load presented to the engine is the resistance of rotating whatever is fouling the prop through the water its immersed in.
...

You're wrong.
While a dirty prop can be inefficient at transferring thrust to the water, in my experience, it's draggy and absorbs power.
Extreme case, power boat with barnacles on prop won't rev.

It's like a dinghy rudder with weed on it, it will generally still steer the boat, but it slows you down an awful lot.
Instead of acting like a nice aerofoil, the blades of the prop are dumping energy into the water as turbulence.

 

[Gixer]

My personal experience with the 1GM10 is that even a tiny amount of fouling on my prop slows the boat noticeably and gives be black smoke from the exhaust. Once I had my prop badly fouled with weed and the boat practically stopped, the GM preceded to overheat.

 

[Sailing steve]

You're wrong.
While a dirty prop can be inefficient at transferring thrust to the water, in my experience, it's draggy and absorbs power.
Extreme case, power boat with barnacles on prop won't rev.

It's like a dinghy rudder with weed on it, it will generally still steer the boat, but it slows you down an awful lot.
Instead of acting like a nice aerofoil, the blades of the prop are dumping energy into the water as turbulence.

The power a dirty prop is dumping is the power that ought to be propelling the boat instead. If you can't transfer the power from the engine into the water no matter how many revs you pile on you ain't going nowhere.

Which is pretty much what I said.

 

[B27]

It's nothing like wheelspinning on ice, which was your analogy.
You can't 'pile the revs on', because the 'friction' of the prop rotating in the water resists the torque of the engine.

That will happen with say a barnacle encrusted prop which still functions but requires a lot more torque from the motor.

 

[Pye_End]

Power from the engine goes into propelling the boat, and overcoming resistance. When resistance is higher (eg. particularly dirty prop) then more fuel is burned for same revs, and a higher torque at the stern gear. The boat will also experience a reduction in boat speed for the given rpm, which will encourage higher rpm to be used - probably exacerbating the problem.

 

[38mess]

Air getting in the system?

 

[bignick]

Deleted.

 

[slawosz]

I took this video:

Doesn't particulary shows anything bad, as before - on gear when I use 70% or so of throttle, it does not react. The speed is reduced to 4 knots instead of normal 5. I will check propeller next time I will be on the boat - I need a wetsuit for that