BMC 1500 running rough on start up

[Cheshire cat]

I'm trying to help a friend with a BMC 1500. 

 

It recently had new glowplugs and replacement injectors (allegedly refurbished)

 

The symptoms are that on first startup of the day the engine starts easily but  sounds rough. It runs willingly though. After two or three minutes of running the revs will suddenly rise and the engine will run much more sweetly. I am guessing this is when the fourth cylinder decides to join the party. 

 

I think I'm correct in saying that this only started to happen part way through a two week cruise. 

 

My first thought was that maybe a connector had vibrated loose on one of the poer leads supplying the glowplugs or maybe an early life failure of one of the glowplugs. I' have checked the leads. They were all tight. I've taken them off and checked the resistance of the glowplugs. They are all showing 0.7 - 0.8 Ohms which makes me feel they are still good. 

 

I put everything back together and started the engine as expected it was around three minutes before all four cylinders were firing. I let the engine run for a short while whilst scratching my head. I then turned it off and immediately tried to restart it. Yet again it started on three but this time the fourth cylinder joined in within 10 seconds or so late. Subsequent restarts were the same. Fourth cylinder was always 10 seconds late.

 

I'm thinking faulty injector but I can't logically explain what is going on. Any ideas welcome.

Picture of engine attached for what it's worth. 

 

I notice that the injectors are a motly crew. One and two appear to be identical, three looks aftermarket and four has a longer thread on the fuel supply neck so obviously different again. 

[Tracy D'arth]

If you have a mix of injectors it is possible that one or more are Perkins which look very similar but are not correct for the BMC.

They are also slightly longer and you risk the heat shield being broken and dropping into the combustion chamber.

Glow plugs have nothing to do with it once the engine is running.

[Tony Brooks]

Tiny amounts of air getting into the fuel system when the engine is stopped that then gets purged as it runs.

 

Or what Tracy said.

Edited August 9, 2023 by Tony Brooks

[MtB]

23 minutes ago, Tracy D'arth said:

If you have a mix of injectors it is possible that one or more are Perkins which look very similar but are not correct for the BMC.

They are also slightly longer and you risk the heat shield being broken and dropping into the combustion chamber.

Glow plugs have nothing to do with it once the engine is running.

 

If one of the injectors is a Dorothy Perkins and this busted the heat shield on fitting, it's odd the OP says the engine was fine until part way through a two week cruise. 

 

Or maybe they only came to notice it after a few days of use. 

[Cheshire cat]

I hadn't considered air getting in to the system but that feels like a valid explanation. Is it just a question of a gentle tweak of the pipework or do we need new crush washers?

 

Regarding the injectors I would feel happier if we had four identical ones. I note that Tracy has previously stated that the injector nozzles are a different length on BMC compared with Perkins and it is important to buy from someone who knows this. 

 

I was wondering if either of you could recommend anywhere? The boat is currently in the Midlands but willing to travel 50 miles or so for the correct parts if necessary. 

 

MTB makes a valid point. The owner is out of the country at the moment. It was the first trip out since replacement injectors and he only started mentioning the symptoms part way through. I'll see if I can get clarification on that.  

[Tracy D'arth]

Calcutt at Napton?  There must be  a decent diesel service depot in the Midlands

Its not just the length, the nozzles and hence spray pattern is totally different.

 

As the rough running seems to have started after the injectors were changed it would suggest that it is the problem.

Any pipe leaks on the high pressure side would show fuel, air can only get in on the low pressure side before the pump and there would be no need to disturb that pipework to fit injectors.

Edited August 9, 2023 by Tracy D'arth

[Stilllearning]

So an ingress of air would affect all 4 cylinders thus making an injector problem much the most likely answer.

[StephenA]

They do seem to be a mixed set of injectors

Edited August 9, 2023 by StephenA

[Cheshire cat]

Here is an update to muddy the waters. I've been in touch with the owner. The engine had this fault before the glowplugs and injectors were changed. The glowplugs were changed which got rid of a cold start problem. The injectors were replaced because of "running on three" syndrome. Following replacement of the injectors it started on four for a while (only a few starts over a period of a month or so) but has now gone back to starting on three. 

 

If it was air on the high pressure side I would be expecting to be able to see a diesel leak. If it was on the low pressure side I would expect all cylinders to be affected. 

 

I'm blacking my boat tomorrow but when I've got the final coat on I shall have another look. My first thought is to try slackening the nuts on the fuel supply in turn. I'm expecting it not to want to start on two cylinders so that would indicate which cylinder is at fault. 

2 hours ago, StephenA said:

They do seem to be a mixed set of injectors

It's not just the injectors. Look at the nuts on the delivery pipes. They vary in depth too. One and two are the same but three and four are different It's not as though the engine is an old nail. It hasn't done a lot of hours.

[Stilllearning]

Try borrowing 4 proper injectors to see if that fixes it?

[David Mack]

If a replacement (albeit unmatched) set of injectors hasn't changed the problem then its probably nothing to do with the injectors. Which suggests to me that it might be a problem with a valve or perhaps the head gasket resulting in insufficient compression in one cylinder.

When it's running roughly do you get increased white smoke (unburned diesel) from the exhaust?

[Quattrodave]

I too am thinking its air getting into the diesel lines.  I had a similar problem it was a fault mechanical fuel pump.  Not definitive but check your oil level, is it high??

Edited August 9, 2023 by Quattrodave

[MtB]

Given the history now discovered, my money is on low compression on one cylinder. 

 

Time for a compression test, I reckon.

 

 

[Tracy D'arth]

I would expect whoever did the glow plugs and injectors to have done a compression test at the same time but if they were happy to fit such a badly matched set of injectors, probably not.

Check valve clearances before getting too involved.  Feel the compressions by turning the engine over slowly by hand, you can feel the compressions quite well with practice.

[MtB]

1 minute ago, Tracy D'arth said:

Check valve clearances before getting too involved. 

 

Good point. Given the sloppy choice of injectors fitted, could be a valve with no clearance. 

 

Although in my own experience with engines, this is very rare to find. Usually the clearances are just all over the place and clattery. Especially after being 'adjusted' by the owner! 

[Tony Brooks]

I now go along with Tracy and others who suggest lack of compression and potentially the start of a valve problem. Definitely check the valve clearances.

[Cheshire cat]

Thanks all. I'll have a look around for signs of a leak. Failing that my feeler gauges are at home 60 miles away. I was anticipating a glowplug fault so only brought appropriate tools to pursue that line of investigation. I shall be back early next week with a full tool kit. 

 

I've worked on A, B and C series petrol engines but never previously a diesel. On the petrol I would take the plugs out and turn the engine over by hand. How do I go about doing it on a diesel?

 I'm anticipating the compression will be more difficult to overcome. 

 

Someone mentioned unburnt fuel (white smoke). I shall take note today. In my opinion it does throw out an above average amount of black smoke when running on four cylinders, particularly if given some throttle. At the momement I'm thinking the black smoke is a seperate issue. 

[David Mack]

3 minutes ago, Cheshire cat said:

Someone mentioned unburnt fuel (white smoke). I shall take note today. In my opinion it does throw out an above average amount of black smoke when running on four cylinders, particularly if given some throttle. At the momement I'm thinking the black smoke is a seperate issue. 

If its only running on 3 cylinders then the diesel injected into the 4th cylinder should appear as white smoke in the exhaust. But that might be masked by the black smoke!

[Tony Brooks]

25 minutes ago, Cheshire cat said:

've worked on A, B and C series petrol engines but never previously a diesel. On the petrol I would take the plugs out and turn the engine over by hand. How do I go about doing it on a diesel?

 I'm anticipating the compression will be more difficult to overcome.

 

Don't take anything out, just turn the engine over by hand. Ideally by the engine crank pulley nut, or if you must by the alternator pulley nut and push down on the alternator belt. Yes it will be more difficult to turn it through compression than a petrol engine so take your time. You are just trying to find one compression that is less than the rest.

 

If for your purposes too slack valve clearances are unlikely to cause the symptoms, so just set each valve for testing and waggle the valves by hand and if they all have some free movement it is not valve clearances.

 

Nowadays, you can get compression testers that screw into the glowplug holes rather than take the injectors out. A petrol one is not any good.

 

 

 

 

[Eeyore]

6 hours ago, Cheshire cat said:

Thanks all. I'll have a look around for signs of a leak. Failing that my feeler gauges are at home 60 miles away. I was anticipating a glowplug fault so only brought appropriate tools to pursue that line of investigation. I shall be back early next week with a full tool kit. 

 

I've worked on A, B and C series petrol engines but never previously a diesel. On the petrol I would take the plugs out and turn the engine over by hand. How do I go about doing it on a diesel?

 I'm anticipating the compression will be more difficult to overcome. 

 

Someone mentioned unburnt fuel (white smoke). I shall take note today. In my opinion it does throw out an above average amount of black smoke when running on four cylinders, particularly if given some throttle. At the momement I'm thinking the black smoke is a seperate issue. 

You could try holding the key in the heat position for 30 seconds or so after the engine has started. This is of course a fully automatic feature on most modern diesel engines. It reduced the initial smoking and settled the idle to something approaching smooth at lot quicker.

The fault on mine (long gone) was a restriction in the spill line, causing overfueling and carbon blockage of the exhaust ports. But curiously similar symptoms (including the black smoke).

Edited August 10, 2023 by Eeyore

[Tracy D'arth]

Older diesels will produce black smoke when they are under heavy load trying to get up to the speed where the governor reduces the fuel input, like when you quickly open it up.

Any white smoke is unburnt fuel, unless its steam!

[StephenA]

Could it be an injector pump problem?  If there's not a lot of white smoke then is it that the "dead" cylinder isn't getting fuel at all?

[Tony Brooks]

10 minutes ago, StephenA said:

Could it be an injector pump problem?  If there's not a lot of white smoke then is it that the "dead" cylinder isn't getting fuel at all?

 

Personally, I have doubts about that because the rotor, pressure plungers, and governor are common to all cylinders on these rotary, hydraulically governed pumps. If it is the pump, then the only thing that is not common is the drilling to the individual injector connection.

[Cheshire cat]

OK, sorry for disappearing. We have just finished our blacking and put our boat back in the water. I had a chance to look at the BMC again this morning though not with the correct tools yet.

 

I checked the oil level. It is on max. It doesn't smell unduly of diesel.

 

I started the engine. I actually turned the key too far and it fired up without any glowheat. I watched the exhaust and could see a grey mist coming out of it. I had to wait only a minute today before the fourth cylinder fired up and engine revs increased by 200 rpm. Two or three seconds later the grey mist  disappeared confirming to me that all four cylinders were firing correctly.

 

I stopped the engine and restarted it . Back on to three cylinders for 10 seconds and then the fourth cylinder joined in. 

 

I had a brainwave at this point and decided to feel the injectors. The engine wasn't anywhere near normal running temperature but I am sure that the suspect cylinder is number 4. The injector body of number 4 was cooler than the other three. 

 

I've looked at the high pressure pipes and can't see any evidence of diesel weeping. Annoyingly, number four's pipe comes out of the pump underneath the pump body so difficult to see even with a mirror.

 

I shall return with appropriate tools on Wednesday. I measured the crankshaft pulley nut as 1 1/4 AF. Is that correct? I have a suitable socket and bar breaker so should be able to turn the engine over OK.

[Bee]

The thread on the front injector does indeed look longer but it also looks like quite a coarse thread. Don't suppose it could be a different thread and thus giving rise to all sorts of problems could it?