2GM20F revving flat out on it”a own and won’t shut off.

[vas]

thanks for the idea, probably will pass as access to my generator (2GMF) is v.good and I haven't even bothered fitting a system to run the engine stop lever from a distance. I do have a linear actuator running the governor though to get me slowly up to 3000rpm and then slowly close the governor to kill the engine...

 

[scottie]

If it was fully running away you would be in no doubt and pulling the fuel cut-off would do nothing. I guess that it might be possible that you have just a small amount of piston blow-by and it was on the point of limited runaway, supplemented by the fuel, and cutting off the fuel was enough to slow it down.

The only way to stop a full runaway, which is when the engine burns it's own oil, is to deprive the engine of air. This means holding something over the air intake like a gloved hand or a cushion or similar. Not a loose rag as that might just get sucked in to the air intake. It can be difficult to block the intake because the intake air filter might get in the way so I would remove the filter if you have one so you can see the open pipe and the start the engine and be ready to stop it this way if necessary.

If you can find a large wooden or hard rubber bung which fits snugly into the intake but cannot be drawn in, then that is perfect. At the first sign of uncontrolled running just stick the bung in the intake and it will stop within a few seconds. It won't do any harm at all to run without the air filter whilst you get to the bottom of what is going on.

Obviously, now the engine is stopped, check that the cable from the morse control is actually and reliably closing the throttle arm on the side of the engine against its end stop.

A cylinder compression test would also determine if you have excessive blow-by but you would need an engineer with the right equipment to do that.

Richard

i would NOT recommend using a HAND unless wearing a very thick GLOVE
something like a rubble sack might work over the filter and would be quicker than unbolting the filter

 

[RichardS]

i would NOT recommend using a HAND unless wearing a very thick GLOVE
something like a rubble sack might work over the filter and would be quicker than unbolting the filter

I'm not sure why the shouty capitals are necessitated? I said "gloved hand".

I suggested unbolting the filter before starting the engine again so I'm not sure where speed comes into it.

Richard

 

[vas]

can someone explain why not a plain hand?
filter cowl hole is approx 40mm, have touched it after engine warming up properly, was relatively cool to touch (iirc)
is there something else I'm missing?

cheers

V.

 

[Norman_E]

can someone explain why not a plain hand?
filter cowl hole is approx 40mm, have touched it after engine warming up properly, was relatively cool to touch (iirc)
is there something else I'm missing?

cheers

V.

The suction could do you serious damage.

 

[scottie]

I'm not sure why the shouty capitals are necessitated? I said "gloved hand".

I suggested unbolting the filter before starting the engine again so I'm not sure where speed comes into it.

Richard

Surprised that you think that you are the only person that reads replies to your posts and not everyone is as clever with engines!?

 

[vas]

The suction could do you serious damage.

from a 4cm hole? I'd never have thought it can be serious, thanks.
Would by any chance anyone know what sort of volume of air per min such a small say 2cyl engine inhales at 3.6k rpm?
They are around 600cc iirc?
could I say it's .6ltX3600/8 hm, that's 270lt/min I must be wrong, very wrong!

V.

 

[penberth3]

from a 4cm hole? I'd never have thought it can be serious, thanks.
Would by any chance anyone know what sort of volume of air per min such a small say 2cyl engine inhales at 3.6k rpm?
They are around 600cc iirc?
could I say it's .6ltX3600/8 hm, that's 270lt/min I must be wrong, very wrong!

V.

It's too early, I might be missing something! What is the divide by 8, and what does hm mean?

And no, I wouldn't put my hand near a small intake.

 

[vas]

sorry, busy doing other things while posting (typical)
hm is just a typo, meant to say l /m
divide by 8 is more difficult to explain bear with me...
On each crank turn, on a two cyl we have one of the pistons filling with air, the other discharging the bang phase. So, in turn two the one sucking is doing the bung, the other is sucking. Er, means that in two full turns, a 2cyl has sucked air of it's whole capacitance, so, I'm wrong should be divide by 2. Was actually thinking that 8stages are needed to get the full 600cc air drawn in, but these 8 stages are 4 crank rotations and there's an overlap as well, so 2 turns, which makes it even worse at 1080lt per min, surely I'm way off!
someone?

V.

 

[penberth3]

sorry, busy doing other things while posting (typical)
hm is just a typo, meant to say l /m
divide by 8 is more difficult to explain bear with me...
On each crank turn, on a two cyl we have one of the pistons filling with air, the other discharging the bang phase. So, in turn two the one sucking is doing the bung, the other is sucking. Er, means that in two full turns, a 2cyl has sucked air of it's whole capacitance, so, I'm wrong should be divide by 2. Was actually thinking that 8stages are needed to get the full 600cc air drawn in, but these 8 stages are 4 crank rotations and there's an overlap as well, so 2 turns, which makes it even worse at 1080lt per min, surely I'm way off!
someone?

V.

Yes, getting closer!

Just to confirm we're talking 4-stroke, yes? I'll use ltr for litre.

0.6 ltr per cylinder, so 0.6 ltr is drawn in every alternate revolution. 0.3 ltr per rev per cylinder.

 

[RobF]

Yes, getting closer!

Just to confirm we're talking 4-stroke, yes? I'll use ltr for litre.

0.6 ltr per cylinder, so 0.6 ltr is drawn in every alternate revolution. 0.3 ltr per rev per cylinder.

Using the Yanmar manual
Bore x stroke = 75 x 72 (mm)
Displacement = 0.636 ltr

By my reckoning, at 3600 rpm, each piston does one intake, so air requirements = 3600 x 0.636 = 2290 ltrs per minute. This can be halved (as the air is ingested every other stroke. If it takes 4 seconds to stop the engine, it will have tried to ingest 36 ltrs of air (assuming slow down is linear).

 

[penberth3]

Using the Yanmar manual
Bore x stroke = 75 x 72 (mm)
Displacement = 0.636 ltr

By my reckoning, at 3600 rpm, each piston does one intake, so air requirements = 3600 x 0.636 = 2290 ltrs per minute. This can be halved (as the air is ingested every other stroke. If it takes 4 seconds to stop the engine, it will have tried to ingest 36 ltrs of air (assuming slow down is linear).

So vas was right with 1080 litres per minute per cylinder, based on 0.6 ltr. I didn't want to stick my neck out too soon!

 

[RichardS]

Surprised that you think that you are the only person that reads replies to your posts and not everyone is as clever with engines!?

I'm not sure what any of that means ..... but why quote my post?

Richard

 

[Lucky Duck]

Not doubting the calculations but I would have expected a noticable movement of air if that much was being sucked out of the cabin when the engine was working hard?

 

[penberth3]

Not doubting the calculations but I would have expected a noticable movement of air if that much was being sucked out of the cabin when the engine was working hard?

There will be a noticeable movement, if you look for it.

 

[wipe_out]

So I went to the boat today and when I pulled the dipstick there was a flow out of the hole and very runny so definitely diesel in the oil.
Pulled the lift pump and it looks like diaphragm must have gone because there was diesel coming from the back of it.
Glad I found a possible cause so will replace it and put through two oil changes and then see how we go from there.

 

[penberth3]

So I went to the boat today and when I pulled the dipstick there was a flow out of the hole and very runny so definitely diesel in the oil.
Pulled the lift pump and it looks like diaphragm must have gone because there was diesel coming from the back of it.
Glad I found a possible cause so will replace it and put through two oil changes and then see how we go from there.

Always good when you have something obvious to diagnose and deal with!

 

[vas]

So I went to the boat today and when I pulled the dipstick there was a flow out of the hole and very runny so definitely diesel in the oil.
Pulled the lift pump and it looks like diaphragm must have gone because there was diesel coming from the back of it.
Glad I found a possible cause so will replace it and put through two oil changes and then see how we go from there.

good result, now would be interested learning where and for how much you'll get your lift pump please.
FWIW, the original is a Mikuni (a v.reputable Jap brand for carbs and fuel systems)

Also how many hours on the engine?

cheers

V.

 

[RichardS]

So I went to the boat today and when I pulled the dipstick there was a flow out of the hole and very runny so definitely diesel in the oil.
Pulled the lift pump and it looks like diaphragm must have gone because there was diesel coming from the back of it.
Glad I found a possible cause so will replace it and put through two oil changes and then see how we go from there.

That's good news. At least you now have something to work with and have gained some useful tips for the future. Well done.

Richard

 

[Dan Tribe]

The only way to stop a full runaway, which is when the engine burns it's own oil, is to deprive the engine of air. This means holding something over the air intake like a gloved hand or a cushion or similar. Not a loose rag as that might just get sucked in to the air intake. It can be difficult to block the intake because the intake air filter might get in the way so I would remove the filter if you have one so you can see the open pipe and the start the engine and be ready to stop it this way if necessary.


Richard

An elderly uncle was an engineer on submarines. He had a battered tin tea tray kept on proud display. He claimed that he saved the ship by clapping it over the air intake of a runaway engine.