BMC 1.5 smoking at higher revs

[David Mutch]

Hi all,

 

My BMC 1.5 is has started producing large amounts of white smoke (with a very slight blueish hue) at high revs. 

 

It starts OK (although takes more heat than my previous BMC), and There's no smoke at idle, or at tickover or just above, but only when gunning it a bit. Can be slightly lumpy for 30 seconds or so after starting, if put immediately to idle.

 

There's also something that sounds a little like knock, but it's fairly subtle, and it seems to come and go to an extent.

 

My first thoughts were pump timing, compression or injectors.

 

So far I have:

 

1. Replaced injectors with recon ones from Calcutt

2. Checked compression (all between 360-380psi) 

3. Advanced pump timing as far as I can/dare

4. Checked valve clearances

 

The engine is regularly serviced (oil and all filters). And oil pressure is good (at least 50psi at idle).

 

I'm now wondering what's next. I'm thinking:

 

1. Recon fuel pump

2. Timing chain (although decent compression makes me doubt valve timing)

3. Head gasket?

4. New harmonic balancer (crank pulley). I've had similar noises in cars caused by that going, but not sure it explains the smoke

 

Any comments/suggestions would be most welcome!

 

Edited January 16, 2022 by David Mutch
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[Mad Harold]

Had similar wth my BMC 1500.Used at canal speeds there was no smoke,but on opening up a bit on the river,it produced enough smoke to obscure the river behind.

The smoke used to subside after a while and after about five minutes was smoke free.

I think the smoke was caused by long periods of running at low power settings causing a build up of soot and carbon in the combustion chambers and exhaust manifold.

If you can stand the noise and vibration, then I think it is a good idea to give the engine a bit of a thrashing now and then.

[David Mutch]

4 minutes ago, Mad Harold said:

Had similar wth my BMC 1500.Used at canal speeds there was no smoke,but on opening up a bit on the river,it produced enough smoke to obscure the river behind.

The smoke used to subside after a while and after about five minutes was smoke free.

I think the smoke was caused by long periods of running at low power settings causing a build up of soot and carbon in the combustion chambers and exhaust manifold.

If you can stand the noise and vibration, then I think it is a good idea to give the engine a bit of a thrashing now and then.

Thanks Mad Harold. Doesn't seem like carbon deposits being cleared out. Much more like unburned fuel. Recently took her down to Bristol on the Avon, so she got a good run there, and that didn't improve the situation, I'm afraid

[Tony Brooks]

The 1.5 does not have a harmonic balancer, I think that you are referring to the torsional oscillation damper. Harmonic balancers run on a separate shaft. I could see that if the rubber is badly degraded it could make a ticking/knocking sound but I agree, I can't see it making smoke.

 

If you had said blackish smoke I would have suggested it was overloading so indicating an overlarge prop but not for white smoke. I assume this is a dry exhaust boat but if it is a wet exhaust this could be a lack of raw water causing steam. If you do have a wet exhaust report back and I will say more.

 

You seem to have done all the sensible things apart from fully advancing it but It would  be sensible to check the smoke at a variety of injection timing positions.

 

The knock could be timing chain slap so maybe take the timing cover off for inspection. I am wondering if the skew gear oil strainer and jet are blocked so the skew gears on the camshaft and injector pump drive shaft are badly worn. That would retard the injection at higher speed. You could pull the pump shaft to inspect the skew gear as long as you ensure the pointer on the mounting block is properly aligned with the line scribed on the pump flange and note the position of the master spline before you pull the shaft so you can put it back in the same position. With the pump off I think it is a recessed countersunk machine screw that holds the mounting block onto the side of the engine. Definitely check and clean the oil jet and strainer if you have never done it

 

 

[David Mutch]

5 minutes ago, Tony Brooks said:

The 1.5 does not have a harmonic balancer, I think that you are referring to the torsional oscillation damper. Harmonic balancers run on a separate shaft. I could see that if the rubber is badly degraded it could make a ticking/knocking sound but I agree, I can't see it making smoke.

 

If you had said blackish smoke I would have suggested it was overloading so indicating an overlarge prop but not for white smoke. I assume this is a dry exhaust boat but if it is a wet exhaust this could be a lack of raw water causing steam. If you do have a wet exhaust report back and I will say more.

 

You seem to have done all the sensible things apart from fully advancing it but It would  be sensible to check the smoke at a variety of injection timing positions.

 

The knock could be timing chain slap so maybe take the timing cover off for inspection. I am wondering if the skew gear oil strainer and jet are blocked so the skew gears on the camshaft and injector pump drive shaft are badly worn. That would retard the injection at higher speed. You could pull the pump shaft to inspect the skew gear as long as you ensure the pointer on the mounting block is properly aligned with the line scribed on the pump flange and note the position of the master spline before you pull the shaft so you can put it back in the same position. With the pump off I think it is a recessed countersunk machine screw that holds the mounting block onto the side of the engine. Definitely check and clean the oil jet and strainer if you have never done it

 

 

Thanks Tony.

 

Yes, it's a dry exhaust.

 

What do you mean by 'fully advanced'? I believe I've advanced the pump timing and not retarded it, although it seems difficult to find an authoritative source for which way is which. I've turned the pump maybe one or two degrees clockwise, relative to the block. I'm not sure there's sufficient play in the pipes, especially to the fuel filter housing, to go any further.

 

The noise could be timing chain, but I've been over the engine with a stethoscope to try to pinpoint its source and can't really narrow it down, except it seems worst when I'm directly above the engine. I'd suspect something in the valve train, but taking the oil filler cap off and putting an ear to it doesn't seem to reveal the source.

 

I have to admit I've not checked the oil strainer for the skew gear. Always meant to, but not sure exactly which one it is! Are you able to give directions?

 

I hope I've not ruined my camshaft! If there's wear, do you think it's likely that a new pump will take up sufficient slack?

[Tony Brooks]

1. I just don't think it is sensible running the pump timing at the extremes of the adjustment. The pump is driven in the same direction as a BMC petrol engine distributor, which I think is anti-clockwise, but don't quote me on that, i may well be wrong. So lets say I am correct then turning the pump body clockwise =  advance and anti-clockwise = retard.

 

2. You seem to have pretty much ruled out a slapping chain.  Is there any chance you are hearing diesel knock? That can tend to come and go according to engine temperature, load and speed.

 

3. Look on the block side below the rear (No.4) exhaust duct. You will see a hexagon set horizontally on top of a long bulge in the block  side, that is the strainer, just undo it. A bit lower down there is a (smaller I think) verticl hexagon. That is the oil jet.

 

4. As long as the oil & filter change intervals have been observed I doubt that you have damaged the skew gears but if by some chnace you have then I can't see how a new pump can make any difference. The pump is splined onto the driveshaft that has the skew gear on it so if the gear is worn then there is nothing to take up the excess play.

 

I can't see how anything to d with injector pump operation can have anything to do with this unless the automate you are hearing diesel knock? That can tend to come and go according to engine temperature, load and speed.

 

Most diesels control their speed simply by volume of fuel supplied so unless something like a fouled or oversized prop prevents it send more fuel and the engine speeds up, less fuel and it slows down. in any case white "smoke is not excess fuel. It might be vaporized fuel but you minimized that chance by fitting the new injectors. It might be a low injection pressure but again the new injectors tend to rule that out. I wonder if it is steam from a head gasket problem or similar? You seem to know what you are about so how abut testing the coolant for hydrocarbons, test fluid is available.

 

 

[David Mutch]

15 minutes ago, Tony Brooks said:

1. I just don't think it is sensible running the pump timing at the extremes of the adjustment. The pump is driven in the same direction as a BMC petrol engine distributor, which I think is anti-clockwise, but don't quote me on that, i may well be wrong. So lets say I am correct then turning the pump body clockwise =  advance and anti-clockwise = retard.

 

2. You seem to have pretty much ruled out a slapping chain.  Is there any chance you are hearing diesel knock? That can tend to come and go according to engine temperature, load and speed.

 

3. Look on the block side below the rear (No.4) exhaust duct. You will see a hexagon set horizontally on top of a long bulge in the block  side, that is the strainer, just undo it. A bit lower down there is a (smaller I think) verticl hexagon. That is the oil jet.

 

4. As long as the oil & filter change intervals have been observed I doubt that you have damaged the skew gears but if by some chnace you have then I can't see how a new pump can make any difference. The pump is splined onto the driveshaft that has the skew gear on it so if the gear is worn then there is nothing to take up the excess play.

 

I can't see how anything to d with injector pump operation can have anything to do with this unless the automate you are hearing diesel knock? That can tend to come and go according to engine temperature, load and speed.

 

Most diesels control their speed simply by volume of fuel supplied so unless something like a fouled or oversized prop prevents it send more fuel and the engine speeds up, less fuel and it slows down. in any case white "smoke is not excess fuel. It might be vaporized fuel but you minimized that chance by fitting the new injectors. It might be a low injection pressure but again the new injectors tend to rule that out. I wonder if it is steam from a head gasket problem or similar? You seem to know what you are about so how abut testing the coolant for hydrocarbons, test fluid is available.

 

 

Thanks Tony. 

 

1. Yes, I guess running at extremes of pump timing is not great, and liable to just be masking an underlying problem. Might be good as a diagnostic tool, though. I guess my question was a bit daft, since I now realise there's a pretty clear limit to how much you can adjust pump timing, dictated by the slots in the pump body!

 

2. I'm not sure I can say I've ruled out the timing chain. Inspecting it is definitely on the to do list. It does sound more like diesel knock, but given the other symptoms suggest retarded timing, something about that doesn't quite make sense to me.

 

3. Thanks! I've been looking at the wrong side of the engine!

 

4. Ah, I was thinking maybe a new pump came with a new shaft with a new gear on it, so I'd be replacing at least half of the worn gears if I changed the pump, but from what you say I guess the gear is all internal, so can't be changed without a major overhaul. I've certainly changed the oil and filters regularly. However, it's a 30 year old boat, so I can't speak for previous owners, although it didn't smoke like this when I bought it.

 

I do have one of those kits for checking for exhaust gas in the cooling system. Will try it, but it doesn't loose coolant, there's no mayonnaise in the oil, no visible bubbles coming up and compression is good, so head gasket seems less likely to me than some kind of timing issue.

 

Thanks again for your advice. This one is really bugging me, as the symptoms and diagnostic tests don't seem to paint a clear or even particularly coherent picture. Will report back with further findings

[Tony Brooks]

I think that if you had a stethoscope on the timing cover it would have been really obvious if the chain was slapping about.

 

FWIW when we had worn skew gears both the camshaft gear and pump drive gear were really badly chewed up and I think just replacing one of them would get that one quickly chewed up.

[David Mutch]

14 minutes ago, Tony Brooks said:

I think that if you had a stethoscope on the timing cover it would have been really obvious if the chain was slapping about.

 

FWIW when we had worn skew gears both the camshaft gear and pump drive gear were really badly chewed up and I think just replacing one of them would get that one quickly chewed up.

Fair play (if you'll pardon the pun). 

 

I've attached a picture of the oil strainer and jet as they came out. A few chunks of carbon, but not excessively gunged up. Could easily blow air through both, and a bit of brake cleaner got them looking sparkling clean in a few seconds, so maybe there's hope for my camshaft. TBH, the symptoms came on fairly suddenly, rather than gradually, as I would expect from that kind of wear.

 

Head gasket test next, but got to wait for the other half to awake from her Sunday afternoon nap before firing the engine up!

[Tony Brooks]

That is good, very nearly rules out worn gears.

[David Mutch]

And I think this makes head gasket less likely

[David Mutch]

These videos give some idea of the sound, although I'm not sure they will capture it completely. Maybe just totally ordinary diesel knock, but I'm pretty sure it's not always sounded like that. Will try to get one of the smoke when I get a chance in daylight

 

[Tony Brooks]

Hard to tell from video sound but that sounds like diesel knock to me. Also your torsional oscillation damper seems in very good order.

[Tracy D'arth]

They may be "fresh" injectors but white smoke is unburnt fuel suggesting a misfire. Are you sure about the injectors? Are they real BMC 1.5D injectors and not the Perkins that look just the same? The Perkins injectors are different and NOT interchangeable. Where did the come from? You say Calcutt which should be correct but even seasoned engine guys have been known to confuse them.

[David Mutch]

16 minutes ago, Tracy D'arth said:

They may be "fresh" injectors but white smoke is unburnt fuel suggesting a misfire. Are you sure about the injectors? Are they real BMC 1.5D injectors and not the Perkins that look just the same? The Perkins injectors are different and NOT interchangeable. Where did the come from? You say Calcutt which should be correct but even seasoned engine guys have been known to confuse them.

Hi Tracy. They're from Calcutt Boats, so I suspect they're the right ones. The noise and smoke were happening before I changed them, and haven't noticeably improved since, so it would be a bit of a coincidence if they were the incorrect ones, and happened to cause the same symptoms as the old ones

[David Mutch]

1 hour ago, Tony Brooks said:

Hard to tell from video sound but that sounds like diesel knock to me. Also your torsional oscillation damper seems in very good order.

I suppose the question is: Is it excessive diesel knock? It certainly seems louder than my previous BMC, and I think this engine has got louder recently, seemingly coinciding with increased smoke. 

 

Could the timing being too far advanced cause smoke? (I've always thought advanced timing would cause knock and retarded timing would cause smoke/a misfire). When I first got the boat, it ran quite rough when cold. I found the pump timing was a couple of degrees retarded (by the timing mark), adjusted and it ran nicely for a long time. Just wondering if actually the pump should be a little retarded, and there was something else that was causing the rough running. If whatever that was (maybe bad fuel?) sorted itself out somehow, that might mean I'm now running too advanced. 

 

I realise I'm clutching at straws a little here ...

[magnetman]

I've got a pair of BMC 1.5s in one of my boats. 

 

Have had a problem with one of them since I got the boat a couple of years ago. Knocking sound and a bit of smoke but not excessive. 

 

I investigated the tappets and found that some of the screws were soft so replaced them and also I recently discovered that one of the rocker arms has a completely nackered bush. 

 

Ordered new one and will be dismantling and refitting. 

 

I'm not one to regularly take engines apart but I was surprised how much of a knocking noise badly adjusted tappets make. 

 

With the bush inside the rocker being completely worn out it is actually impossible to get correct tappet clearance on that one. I did think it might have been a sticking valve. 

 

Interesting to see if replacing the bush does sort it. Will also check the oilways in the rocker shaft itself. 

 

One day all of this will be electric and just plug a computer in to sort it out

 

 

 

Edited January 16, 2022 by magnetman

[David Mutch]

3 minutes ago, magnetman said:

I've got a pair of BMC 1.5s in one of my boats. 

 

Have had a problem with one of them since I got the boat a couple of years ago. Knocking sound and a bit of smoke but not excessive. 

 

I investigated the tappets and found that some of the screws were soft so replaced them and also I recently discovered that one of the rocker arms has a completely nackered bush. 

 

Ordered new one and will be dismantling and refitting. 

 

I'm not one to regularly take engines apart but I was surprised how much of a knocking noise badly adjusted tappets make. 

 

 

 

 

 

Thanks Magnetman. I have checked valve clearances and had a good listen to the top end and tappet chests, so I don't think it's that, although the sound kind of fits.

 

Curious to know what you mean by the screws being soft?

 

I guess something else in the top end could be the cause of the smoke, e.g. valve stem oil seals, but the smoke is definitely more white than blue, and it's only at high revs, so that one is lower down the list of suspects. 

[Tony Brooks]

49 minutes ago, David Mutch said:

I suppose the question is: Is it excessive diesel knock? It certainly seems louder than my previous BMC, and I think this engine has got louder recently, seemingly coinciding with increased smoke. 

 

Could the timing being too far advanced cause smoke? (I've always thought advanced timing would cause knock and retarded timing would cause smoke/a misfire). When I first got the boat, it ran quite rough when cold. I found the pump timing was a couple of degrees retarded (by the timing mark), adjusted and it ran nicely for a long time. Just wondering if actually the pump should be a little retarded, and there was something else that was causing the rough running. If whatever that was (maybe bad fuel?) sorted itself out somehow, that might mean I'm now running too advanced. 

 

I realise I'm clutching at straws a little here ...

 

Well, if Tracy is correct about the Perkins nozzles then the spray pattern may not give a fast initial fuel ignition so it would knock more and probably smoke. The incorrect nozzle thing is a known problem.

 

Diesel knock is the result of the delay period which is the time between fuel starting to inject and actually igniting. This results in more unburnt fuel in the cylinder that all ignites almost instantaneously. The knock is the pressure wave caused by the fuel all burning at once. This can be made worse by lower cetane rated fuel and the cetane rating will vary batch to batch. As far as I know the injection timing tends not to affect diesel knock like ignition timing does on a car. Pinking and diesel knock are two totally different things.

 

Incorrect injection timing is more likely to cause bad starting, loss of power and/or smoke that could be black or light grey.

[Tony Brooks]

When you changed the injectors did you ensure the inverted top hat heat shields that often come out on the injectors were all in place. If one is missing that would give low compression in that cylinder and thus white smoke.

 

Also did you remove the old top hat crimped washers from the bottom of the top hats and fit new. These are steel, not copper. Did you refit the copper washer that fits around the nozzle.

[David Mutch]

Just now, Tony Brooks said:

When you changed the injectors did you ensure the inverted top hat heat shields that often come out on the injectors were all in place. If one is missing that would give low compression in that cylinder and thus white smoke.

 

Also did you remove the old top hat crimped washers from the bottom of the top hats and fit new. These are steel, not copper. Did you refit the copper washer that fits around the nozzle.

Thanks Tony. Yes, replaced all washers (the atomisation/crush washers, large copper washers and spill rail washers). The top hats all remained in the head.

 

It seems very unlikely to me that it's the injectors. It ran fine for years with the old ones, so I guess they were the right type, and it would seem odd for the new ones to be the wrong ones, but to cause the exact same symptoms as the faulty but correct old ones.

[john.k]

I dsay you have a buildup of oil  wet  carbon sludge in the exhaust........apply heat and you have bulk smoke.....A simple test is to run a finger round the exhaust outlet......if wet black goo,then thats oil thats going to smoke when hot.

[David Mutch]

5 hours ago, john.k said:

I dsay you have a buildup of oil  wet  carbon sludge in the exhaust........apply heat and you have bulk smoke.....A simple test is to run a finger round the exhaust outlet......if wet black goo,then thats oil thats going to smoke when hot.

Hmm... That's an interesting theory, which I'd seriously entertain, were it not for the fact I had my exhaust replaced fairly recently, and it didn't improve. Also, I guess I'd expect it to smoke all the time when up to temperature if that were it. I will do the finger test though. Thanks John

[Tracy D'arth]

Arrange a separate fuel supply from a small tank and use clean diesel or better still clean diesel with 25% kerosene. see if it smokes on that. If its OK you have some degraded fuel in the tank.

[john.k]

Another possible cause of  white smoke/unburnt diesel in the exhaust (which should be obvious -eyes watering fumes) is engine running stone cold....which can happen in marine engines...............in any case,what is the fumes/smoke?.......oil/diesel /or water/?.......you should be easily able to smell the difference.....if not ,run the exhaust thru a rag over the outlet for a minute......and smell that.

Edited January 17, 2022 by john.k