Runaway diesel

[webcraft]

.
Was down the boatyard yesterday working on Avy-J. Across the yard a friend was trying to get an old Volvo engine running that had not run for 6 years.

I heard the engine fire into life and said to Catherine, let;s go and have a look. My pal seemed to be revving the nuts off the engine as we walked across, and there was a lot of smoke. Then I heard the shout for help.

Shot up the ladder to find my mate with a small headwound and a considerable panic on. The engine was a 3 cylinder and he only had two hands. He was crouched over the runaway beast with hands over two of the three air intakes but no way of blocking the third. The eninge must have been doing over 4,000 rpm with air only getting to one cylinder.

'Shove your hand over there' he shouted, removing his hand from the aftmost air intake. My hand was sucked hard onto the metal orifice an Robbie with his one now free hand ripped the air filter off the third intake then blocked it with said hand. The engine died almost immediately. I suspect no damage will have been done by the runaway, but now he needs to find what caused it. Immediate investigation was limited to checking the oil . . . up to the mark on the dipstick but somewhat emulsified. Further investigation was abandoned as the shocked owner went home and took whisky.

Made me think. The Yanmar in Avy-J has decompression levers, which would stop the engine in the event of this happening. It also only has a single air inlet even though it is two cylinder, so much easier to smother. But on Fairwinds the Beta has no decompression l;vers. I think I might get a CO2 extinguisher for precisely this eventuality.

Interesting . . .

- W

 

[stevie69p]

It's a bit scary right enough. Had it happen on a van I was working on that must have had a blown turbo and it just took off running on the engine oil. Never have I ripped an air box off so fast and stuck my hand over the intake. Even then I couldn't get quite enough of a seal to stop it, it just slowed down. Had to shout for a colleague to jump in and stick it in 4th gear to stall it.

 

[lw395]

EeeK!
I've heard that you can do serious harm to yourself using your hand across an air inlet in this way.
Engines and boats are cheap by comparison.

 

[rotrax]

I'm going to get a piece of plywood that can be put over my intake to stop the engine.

You both had a lucky escape-I met a guy who had one run away like that, the engine threw a rod and shrapnel entered his thigh after passing through his filthy and very greasy overalls.

He developed gangrene and lost a leg.

Ouch......................

 

[prv]

I'm going to get a piece of plywood that can be put over my intake to stop the engine.

Mine has a single inlet pipe into the air filter which looks about the right size to be blocked by a tennis ball. I did think of hanging one nearby just in case, but with a nearly-new modern engine it felt just a little too paranoid.

Pete

 

[Balbas]

EeeK!
I've heard that you can do serious harm to yourself using your hand across an air inlet in this way.
Engines and boats are cheap by comparison.

Air pressure at sea level in a standard atmosphere is a smidge under 15psi. Unless my schoolboy physics has escaped me, you can't get lower than an absolute vacuum, so the maximum pressure differential is going to be what? 15psi? Should be alright.

 

[simonfraser]

Air pressure at sea level in a standard atmosphere is a smidge under 15psi. Unless my schoolboy physics has escaped me, you can't get lower than an absolute vacuum, so the maximum pressure differential is going to be what? 15psi? Should be alright.

as long as your hand does not fit down the hole = tennis ball ??

 

[davidpbo]

I was just thinking I must add runaway precautions to my roundtuit list.

-Then remembered I have a petrol outboard as my main engine ?

 

[Balbas]

as long as your hand does not fit down the hole = tennis ball ??

its 15psi, not 150psi. And what do you think your little boat engine will do? Ingest your whole arm through an inlet port? A big shipboard diesel engine, yeah I'd exercise some proper caution. My little 33hp donk (which is not atypical in a yacht), not so much. I wouldn't get in the way of the whirly bits for sure, but sticking my hand over the intake wouldn't make me think twice.

 

[dom]

A friend of me in the army told me about a standard little yacht engine (c.100hp) which also powers generators, pumps, and so on. One of them ran away having been inadequately maintained.

Exploding engine blew bits out of its sides and he reckons that anybody unfortunate to have been close by would have risked a serious oil contaminated injury.

Prob best to operate from behind a bed mattress if poss (better than nothing), stuff something into the air intake, and peg it!

 

[cpedw]

Would fuel shut-off not be simpler and usually a bit remote from the engine? It may take longer but might be safer for the operator(s),

Derek

 

[Stemar]

The most common cause of a runaway is sump oil getting into the cylinders, not an excess of diesel, so turning the fuel off would have no effect.

 

[cpedw]

You're right. It's too early for me!

 

[dom]

The most common cause of a runaway is sump oil getting into the cylinders, not an excess of diesel, so turning the fuel off would have no effect.

Indeed, with the danger point occurring at way overspec revs, rising temp, and a dwindling oil supply

 

[webcraft]

its 15psi, not 150psi. And what do you think your little boat engine will do? Ingest your whole arm through an inlet port? A big shipboard diesel engine, yeah I'd exercise some proper caution. My little 33hp donk (which is not atypical in a yacht), not so much. I wouldn't get in the way of the whirly bits for sure, but sticking my hand over the intake wouldn't make me think twice.

It sucked fairly hard on the palm of my hand and left a ring which took a couple of minutes to fade, but didn't feel as though it was about to ingest me. Would be happy to stop an engine again with a hand/hands over the air intake after that experience, but a CO2 extinguisher might be a better way.

Re. cpedw's comment - the fuel was already shut off . . . .

- W

 

[rotrax]

Our donk is a bigger Turbo Yanmar-110 HP. The intake is across the rear of the engine, above the gearbox. I have realised it would take a minute to remove the air filter-a round one with cleanable mesh. It has a centre screw and a supporting bracket.

In my case, I will make a hard plastic sleeve that can be slipped over the air cleaner mesh to stop the air.

I would never get the air cleaner off in time!

 

[webcraft]

Our donk is a bigger Turbo Yanmar-110 HP. The intake is across the rear of the engine, above the gearbox. I have realised it would take a minute to remove the air filter-a round one with cleanable mesh. It has a centre screw and a supporting bracket.

In my case, I will make a hard plastic sleeve that can be slipped over the air cleaner mesh to stop the air.

I would never get the air cleaner off in time!

CO2 extinguisher would do the job as well?

- W

 

[oldharry]

Our donk is a bigger Turbo Yanmar-110 HP. The intake is across the rear of the engine, above the gearbox. I have realised it would take a minute to remove the air filter-a round one with cleanable mesh. It has a centre screw and a supporting bracket.

In my case, I will make a hard plastic sleeve that can be slipped over the air cleaner mesh to stop the air.

I would never get the air cleaner off in time!

Hard plastic wont seal it properly. Had an old Sherpa with the Perkins 2.0l Perama still found on older boats that needed frequent oil top ups. We kept the spare oil in its plastic container in the engine compartment. One day the engine lost nearly all power and started emitting huge clouds of smoke. With sinking heart I pulled over, stopped, and found the plastic oil can had fallen against the air intake. Removed it and carried on. The point being that the hard plastic did not seal it enough to stop the engine altogether as Rotrax hopes.

Later the same engine ran away on oil blown up the breather tube into the inlet manifold, where it pooled until I came to a hill needing a bit more welly. switching off made no difference (scary!) but fortunately it sucked the air inlet dry of oil and stopped. It ran a good few thousand miles more none the worse for over revving - after that we diverted the breather via an old oil can to collect the oil. At the end we were collecting nearly a litre of oil every 50 miles, so would stop and use it to top up the sump again! Eventually we treated it to a rebore which solved the problem, but the workshop (Panda engineering in Portsmouth) found absolutely no damage anywhere from the runaway, which it did 2 or 3 times before we took pity on the poor beast, and threw some money at it! Crank etc all good and entirely OK for regrinding. Valves etc also all found to be undamaged though they must have been bouncing like tennis balls during the run aways!

 

[ghostlymoron]

I would have thought the engine could generate a suction - negative pressure - so the difference would be greater than 15.7psi. I wouldn't fancy sticking my hand over the air inlet, I'd use a cushion, towel or anything else soft and pliable.

 

[scottie]

And I thought that ALL trained persons working with engines were warned of the dangers of putting hands near air inlets or unguarded belts etc as a basic!