Page 1 of 1

Diesel runaway

Posted: Sun Apr 28, 2019 9:59 pm
by Nick
.
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 . . .

Re: Diesel runaway

Posted: Tue Apr 30, 2019 7:52 am
by SteveN
I wouldn't fancy putting my hand over the air intake of anything but a very small engine so a CO2 extinguisher is a good idea.
That said I would think that diesel runaway is extremely rare in naturally-aspirated marine diesels, it's very much the preserve of turbocharged engines where the turbo oil seals fail and let engine oil get forced into the inlet side of the engine.
Very (VERY..) badly worn inlet valve oil seals might be a cause but you'd have to have been ignoring serious smoking for a long time before they reached that state. Other than that a serious overfilling of the engine oil perhaps.

Re: Diesel runaway

Posted: Tue Apr 30, 2019 8:08 am
by NorthUp2
Jammed fuel rack or cold start mechanism would be one place to start investigating.

Re: Diesel runaway

Posted: Tue Apr 30, 2019 8:32 am
by marisca
Then there is the backward running donk spewing black smoke out the air intake.

Re: Diesel runaway

Posted: Tue Apr 30, 2019 10:11 pm
by BlowingOldBoots
A small Chalwyn valve, or positive air shut off valve, is designed to stop air flow into a runaway engine. They can be bought second hand for less than £100. Something to consider or have a plan to stuff something into the air intake. I don't think a CO2 extinguisher would work.

http://www.chalwyn.com/tenants/chalwyn/ ... LowRes.pdf

Re: Diesel runaway

Posted: Wed May 01, 2019 6:47 am
by Jonas
I'm also not sure about CO2, and I'm not convinced that compression lifters would stop a seriously racing engine.
The stop solenoid shuts off fuel flow, that could be pushed in manually and held in place until the engine stops.
I think too much thought is going into something that is extremely unlikely to occur.

Re: Diesel runaway

Posted: Wed May 01, 2019 8:25 am
by BlowingOldBoots
Jonas wrote:I'm also not sure about CO2, and I'm not convinced that compression lifters would stop a seriously racing engine.
The stop solenoid shuts off fuel flow, that could be pushed in manually and held in place until the engine stops.
I think too much thought is going into something that is extremely unlikely to occur.


Stopping the fuel supply does not stop the overrunning engine as the engine is sucking up engine oil from the sump via the rings on the down stroke and then compressing it on the up stroke, at which points it ignites. This is why you must have an air shut off device. On drilling rigs where gas release is a risk, small utility engines can run away on the gas in air inlet, hence thats a second reason for fitting one, but not relevant to yachts.

Re: Diesel runaway

Posted: Wed May 01, 2019 9:20 am
by wully
I used to work with a bloke who built his own 2 stroke diesel out of an old ford cortina engine - it WAS a wee while ago now right enough..

Anyway, he modified the cylinder head , timing and whatever else and bolted it all back together. Carbs wouldn’t work so he cobbled together a pressurised fuel system with an old scuba bottle....cracked open the pillar valve and cranked the engine which was bolted directly onto his shed bench.

Much to his surprise it fired up and started to splutter along, then got going ....and going and going. He closed in the pillar valve but the charge in the system kept it running faster and faster.

He ran for it when the engine started ripping its way off the bench. The resultant small explosion and fire destroyed the shed and his dream of cheap commuting.

Re: Diesel runaway

Posted: Wed May 01, 2019 3:22 pm
by Jonas
Thanks BoB, I live and learn.

Re: Diesel runaway

Posted: Wed Jun 12, 2019 12:27 pm
by steveyates
we had this issue in my mates twister last month, which meant having to come back under sail from the treshnish isles to glencoe, (cept we ended up in oban after 2 days when the wind died completely, but thats another story) It is indeed the engine running on oil, and the fuel stop makes no difference. Suspect was a replacement lift pump, he got a chinese one rather than a yanmar one, and seems to have fixed it. But he now has water getting into his oil as of yesterday.

That engine ran all last year, ever since he had the head off it and replaced various parts to give it a good overhaul and service, he's had nowt but problems.

Re: Diesel runaway

Posted: Thu Jun 20, 2019 12:27 pm
by Gordonmc
My Land Rover Discovery, company car, had a runaway which all but destroyed the engine.
Fortunately I was not driving at the time as a work colleague had borrowed it to go to a job.
He got to a section of dual carriageway and managed to pull into a layby when the revs started red-lining.
Absolutely nothing he could have done apart from getting out and waiting.
It took quite a while for the engine to die.
The rather clueless company MD at the time tried to blame the breakdown on failure to check the oil, saying the recovery truck driver told him there was no oil in the sump.
I put him right.
The Disco was sold to an engineer friend of mine who rebuilt the engine.
Scary.

Re: Diesel runaway

Posted: Thu Jun 20, 2019 10:38 pm
by Aja
This also happened to me on a friend's boat fitted with a Yanmar YSM12 which has a horizontal cylinder. We were motorsailing through the Narrows at the top of the Kyles of Bute with the main up. It was a bit gusty and got hit by a gust. Before we could dump the main the boat heeled over considerably which started the process. Engine really revved it's head off with clouds of black smoke from the exhaust.

Friend managed to stop the engine using a polypropylene cutting board which he had handy which he held over the air intake. Engine was knackered but subsequently rebuilt. I was always very wary after that as I had the same engine when we had Rebel. I changed our engine for a 2GM20F soon after that.

I don't thing the horizontal cylinder helped.

Donald