BMC 1.5 wouldn't stop

[marktrend]

Hi,

 

I have a BMC 1.5 engine in my boat. It has always been a little temperamental - chiefly problems with overheating (which is still an occasional issue despite having changed thermostat, waterpump, coolant hose), and I had its starter motor overhauled a few months ago.

 

Last week, very soon after starting a journey, I started getting very thick white/ grey smoke from the exhaust. I did the sensible thing and stopped, moored up, looked up possible theories on this and other forums, and called a widely recommended engineer to come and do the full engine service I had been planning to get done at the end of the month. He is a very busy man and so hasn't been able to get over yet, but I talked to him for a while and he suggested that it could just be a bit of condensation in the engine, as it has been extremely cold and the engine hadn't been run for 10 days or so. The 'smoke' had dissipated pretty quickly after stopping the engine, and from what I had read that was in line with it being steam mixed in with the exhaust fumes.

 

That didn't sound too bad, so today I decided to risk running the engine, just to warm it up and see if the problem righted itself after a while.

 

It didn't.

 

I started the engine, giving it some throttle to start as that always helps it start usually. Then when it had started, I dropped the throttle so it could tick over. I noticed two things - the exhaust was pouring out thick smoke again, and the revs had not dropped. If anything, they were increasing. I pulled the engine 'stop' cord. Nothing. The engine at this stage is going faster than I've ever heard it. I did not have the presence of mind to look at the dials, but had half a memory that fumes in the engine room can feed the engine and make it keep running, so I lifted the floor (it is a cruiser stern boat) in the vague hope that the 'fuel' carrying fumes would escape the engine.

 

At this point, I have to confess I just panicked and legged it. I really can't be sure of what colour the smoke was, as I was too busy having visions of the whole thing blowing up... But I think it was darker than before.

 

The engine must have run for a couple of minutes like this and then stopped of its own accord. I dare not try it again. I had a look in the engine bay after returning to the boat and there is oil on the floor, but I don't know what that signifies.

 

Anyway, apologies for this long winded tale but trying to get all the info out there. I'm trying to get in touch with the mechanic but can't get hold of him, so in the meantime... any ideas?

 

Many thanks in advance for any theories you might have.

 

Mark

[alan_fincher]

If it continues to run after you have denied it fuel by activating the stop control, there is a danger it is actually managing to burn its own engine oil as fuel.

 

One thing to ask is are you confident it is not overfilled with engine oil - i.e. when the engine is cold, (and assuming you have the correct diptick fitted!), where is the level against the markers?

 

If it is even slightly over "maximum", that is never a good idea, and with BMCs can lead to other different problems too, we are told.

 

You need to be more than a bit careful here, if the engine is romping away with the speed control set to a tick-over speed, and you can't stop it on the stop control, you do risk it destroying itself, and it may not be great to be in close proximity to it if it attempts that.

[Paul C]

Yeah, sounds like its running on its own engine oil, which is somehow getting into the cylinders (eg worn rings). The way to safely stop it is to cut off the air supply, so that's a rag into the air cleaner/air inlet or fire extinguisher fired into there.

 

The thick white smoke before it "ran away" could be head gasket failure? That might well let oil into the cylinders too, depending on exactly how it failed.

 

I think the best approach now is to remove the cylinder head, inspect the gasket and turn the engine by hand to carefully inspect the bores.

[David Mack]

If a BMC 1.5 runs at a fast and constantly varying speed regardless of the throttle setting it can be due, paradoxically, to fuel starvation arising from a blocked filter. The speed governor on this engine relies on the pressure difference generated by pumping fuel through a small hole. If there is insufficient fuel, the fuel flow is reduced, the pressure generated is lower, which the governor interprets as meaning the engine speed is too low, and so causes more fuel to be injected into the cylinders, speeding it up. When I had this problem it turned out that the main fuel filter element had failed, allowing crud to build up on the fine mesh filter on the injector pump inlet. Replacing the former and cleaning the latter solved my problem.

 

That said, the smoke and failure to stop on the stop control suggests your problem may be more fundamental as others have suggested.

[Chalky]

As said above it sounds like "pull over" where the engine draws up oil from the sump and runs with it as fuel. Alternatively it could be leak from an oil gallery into one of the cylinders caused by a gasket fault. If it pull over then it's very serious. I've seen this happen to engines on test beds and it can be terminal if left too long - the engine consumes all of its lubricant then seizes. Get the engine checked by a mechanic before you use it.

Edited March 27, 2013 by Chalky

[Tony Brooks]

If it continues to run after you have denied it fuel by activating the stop control, there is a danger it is actually managing to burn its own engine oil as fuel.

 

One thing to ask is are you confident it is not overfilled with engine oil - i.e. when the engine is cold, (and assuming you have the correct diptick fitted!), where is the level against the markers?

 

If it is even slightly over "maximum", that is never a good idea, and with BMCs can lead to other different problems too, we are told.

 

You need to be more than a bit careful here, if the engine is romping away with the speed control set to a tick-over speed, and you can't stop it on the stop control, you do risk it destroying itself, and it may not be great to be in close proximity to it if it attempts that.

 

 

I would add that I am beginning to see some fuel dilution problems on engines with DPA pumps. I expected this when they pulled the sulphur from the fuel. Every owner with a BMC/Perkins 4-10x should now be keeping a close eye on the engine oil level and if it starts to rise investigate it for dilution with fuel. The oil gets thinner, less oily, and eventually smells of fuel. Main culprits are the shaft seal on the DPA pump or the lift pump diaphragm.

[marktrend]

Thank you both for the swift and informed responses.

 

Overfill - Oil was at exactly maximum on the dipstick before I ran it, so that sounds feasible. That is a boat after all, so I guess a slight tilt to one side could give an inaccurate reading.

 

Head gasket - that has been mentioned before in connection with the overheating. Sounds... expensive.

 

I'm not familiar enough with how the bores should look to competently inspect them, and I would worry that in removing cylinder head I might inadvertantly cause more problems than I solve, so will suggest that theory to a mechanic and let them do it I think.

 

The other problem is that I don't know what stopped the engine from running in the end. But from the sounds of it, this latest incident in itself won't have helped the general health of this BMC.

 

Thanks Tony - will have a look at the oil to see if it is thin or smells of diesel

[marktrend]

Just checked the dipstick and oil level is WAY above max. It wasn't before... which suggests to me that it isn't just oil in there anymore. Whether that is fuel or coolant or what I don't know.

 

For what it is worth the oil is still black, which I gather is normal for a diesel, and not milky, which I understand to be a rule of thumb for blown head gasket - but maybe that is not relevant for this engine.

 

It does look a bit thinner.

 

Can't discern any diesel smell on the dipstick.

[mickp]

milky oil normally water contamination so it must be fuel in there as the engine cant add extra oil to what was already thereso maybe easy fix touch wood

[RickH]

I would bet fuel in the oil , possibly from your lift pump ? Did it stop or did it seize ? I think you may be lucky that the engine didn't carry on until out of fuel .

 

I would also pump out some of this oil into a glass jar and see if it seperates .

[marktrend]

Fuel in oil via lift pump is current favourite working theory. Engine still just about turns with a spanner but does seem pretty stiff... however, that it turns at all I think is reason to be cautiously cheerful.

 

Going to find my oil pump and pump oil out to minimum line on the dipstick, then see if it goes up again overnight (a suggestion over the phone from the very helpful Alan Broomfield).

 

Checking for separation in this pumped out oil is a good suggestion too, so I'll definitely do that.

 

Thanks all

[marktrend]

Pumped out about 5L of oil into a clear plastic bottle. All looks black but will leave it alone to see if it separates by morning.

 

Thanks again to everyone who made suggestions. Will update on here with any developments.

 

Mark

[RLWP]

I can't see why it would separate, it can't hurt to see though

 

Richard

[marktrend]

@RLWP: It would separate if it was part engine oil, part diesel - which would confirm the theory that diesel was mixing with the oil via the lift pump.

[RLWP]

I don't see why the oil would settle out from the diesel, or vice versa. They're both part of the same thing

 

But it might, so why not have a go

 

Richard

[ditchcrawler]

@RLWP: It would separate if it was part engine oil, part diesel - which would confirm the theory that diesel was mixing with the oil via the lift pump.

What I use to light the bonfire doesn't separate out, diesel from filters, oil from oil changers.

[marktrend]

I'll let you know tomorrow. But suspect you might be right Richard, and that even if diesel is in the oil it won't separate for a long time, as the oil may just hold the diesel in place. At least if it doesn't separate, I can rule out water, so still a worthwhile exercise.

[Paul C]

If it does separate, can you let major oil refineries know the details of how you did it, because they've all been wasting time on the costly and inefficient fractional distillation technique for ages...

 

Immiscible fluids separate when left stood - eg oil and water. diesel is oil based, so it will not separate this way.

[marktrend]

Well that clears that up then. Unless the oil refineries haven't tried pouring it into 5L Aqua Pura mineral water bottles, in which case I hereby patent that idea and expect to be a millionaire by breakfast

[J R ALSOP]

Sounds like air in the damper on top of the injector pump, they can either just stop or race off, only had thirty years experience but I have been known to be wrong.

[Chalky]

Well that clears that up then. Unless the oil refineries haven't tried pouring it into 5L Aqua Pura mineral water bottles, in which case I hereby patent that idea and expect to be a millionaire by breakfast

 

Too late - prior art and you've already put it in the public domain!

[marktrend]

Sounds like air in the damper on top of the injector pump, they can either just stop or race off, only had thirty years experience but I have been known to be wrong.

 

That is an interesting theory. Would that also result in the oil level rising - presumably with diesel, as seems to be the case here?

 

 

Too late - prior art and you've already put it in the public domain!

 

Edited March 27, 2013 by marktrend

[Geoff Taylor]

Hi, If you say your oil was ok on the dipstick prior to starting and assuming your engine crankcase breather is not linked up in any way to the air intake then I would guess that the problem could be that something has come adrift in the governor assembly in the injector pump causing overfuelling and unable to stop the engine by usual means.

I hate to be the bearer of bad news but every diesel engine that I have witnessed or stripped after an over run like you have described has received severe damage to valves/pistons/cylinder heads and had even suffered broken crankshafts.

If luck is on your side,prior to any stripping of engine,perform a compression test,this will determine if any valves were bent or cracked a piston when the engine over revved (sorry to be morbid). Get the injector pump tested. Make sure that if the injector pump requires seals that it is fitted with "viton" type seals,they are resistant to bio and low sulphur diesel fuels.

I sincerely hope you avoid any serious damage,best of luck.

[marktrend]

Hi, If you say your oil was ok on the dipstick prior to starting and assuming your engine crankcase breather is not linked up in any way to the air intake then I would guess that the problem could be that something has come adrift in the governor assembly in the injector pump causing overfuelling and unable to stop the engine by usual means.

I hate to be the bearer of bad news but every diesel engine that I have witnessed or stripped after an over run like you have described has received severe damage to valves/pistons/cylinder heads and had even suffered broken crankshafts.

If luck is on your side,prior to any stripping of engine,perform a compression test,this will determine if any valves were bent or cracked a piston when the engine over revved (sorry to be morbid). Get the injector pump tested. Make sure that if the injector pump requires seals that it is fitted with "viton" type seals,they are resistant to bio and low sulphur diesel fuels.

I sincerely hope you avoid any serious damage,best of luck.

 

Thanks Geoff - definitely always best to have all the information, especially from one with first-hand experience of what I might be facing down the line as you do. I'll bear the 'Viton' type seals info in mind should it come to that.

[BlueStringPudding]

If you've still got the oil/diesel combo in plastic water bottles onboard you might want to stash them in something like a bucket. As I learned with nappies I'd used to soak up oil, it can soften some plastics in a surprisingly short space of time, and you could end up with oil where you don't want it. (More oil where you don't want it, should I say).

 

It's something I ought to have remembered from when I left white spirit in a plastic cup in art class at school... Bottom of cup was missing entirely when I next went into class, and so was the white spirit, needless to say

Edited March 27, 2013 by BlueStringPudding