Inconsistent revs (BMC 1800)

[Tracy D'arth]

If you buy a new banjo bolt from a stockist rather than the BMC spares outlets it will not have the 0.5mm hole in it. Calcutt or ASAP may have the correct part or a breaker, all the BMC engines used this CAV filter head, Landrover, Morris, Nuffield tractors etc. 

[Tony Brooks]

I don't often disagree with Tracy because we both seem to have had similar training and experiences but Ido not agree with the comment about your bolt returning too much fuel.

 

The fuel lift pump on your engine was used on the 2.x litre and 3.x litre BMC engines, and I am also fairly sure it was used on the 5.x litre six cylinder. If we ignore the six cylinder one, it still means that it is capable of supplying engines that demand twice the fuel yours does.  Also, once we allow for the depth of the thread engagement, the actual fuel passage will be smaller than that flat suggests. I have seen the 2.2 and 3.x litre engines running with bolts with larger holes that the 0.5mm perfectly satisfactorily.

 

That bolt has been there for years, yet only now have you hit a problem, so that suggests the problem is not the bolt or leak back volume. I would hate for you to spend time and effort trying to source a new bolt and the parts you need while neglecting syphoning out the bottom of the tank. In my view the tank should be your number one priority.

 

[Tracy D'arth]

I'm a pedant though.  Tony is correct, fret not.

[magnetman]

I had a similar thing with one of my BMC 1.5s and it turned out to just be low fuel in the tank and a bad lift pump which wasn't working properly.

Fuel topped up to be above the top of the engine and it worked fine. 

 

Has the fuel level been established in this case? 

 

 

[Tony Brooks]

4 minutes ago, magnetman said:

I had a similar thing with one of my BMC 1.5s and it turned out to just be low fuel in the tank and a bad lift pump which wasn't working properly.

Fuel topped up to be above the top of the engine and it worked fine. 

 

Has the fuel level been established in this case? 

 

 

 

A perfectly valid point, but we know there is a lot of water in the fuel, and we also know taking the fuel filter out and giving it a clean and refitted solved the problem for a short while. Until the tank has been cleaned, I would not want the OP to add more fuel, but checking the level is worth doing.

[David Mack]

54 minutes ago, magnetman said:

I had a similar thing with one of my BMC 1.5s and it turned out to just be low fuel in the tank and a bad lift pump which wasn't working properly.

Fuel topped up to be above the top of the engine and it worked fine. 

 

Has the fuel level been established in this case? 

 

 

Fuel level in the tank below the engine lift pump, and air can leak in through a joint. Fuel level in the tank above the engine lift pump and fuel can leak out through a joint. But the engine will run OK.

[magnetman]

A bad lift pump does not mean a leak. It could be a fault with the diaphragm or a damaged arm. 

Or the valves. 

On my port side 1.5, which seems to have had the lift pump changed possibly for a cheap and nasty one the engine will run fine if fuel level is high enough but problems occur if the level goes below a certain point. 

 

I think the lift pump is bad but its not a big enough problem to be concerned about. The fuel is clean. 

 

 

[Tony Brooks]

45 minutes ago, magnetman said:

A bad lift pump does not mean a leak. It could be a fault with the diaphragm or a damaged arm. 

Or the valves. 

On my port side 1.5, which seems to have had the lift pump changed possibly for a cheap and nasty one the engine will run fine if fuel level is high enough but problems occur if the level goes below a certain point. 

 

I think the lift pump is bad but its not a big enough problem to be concerned about. The fuel is clean. 

 

 

 

It may not be a bad pump as such, it might just be the wrong pump for your engine. Apart from some weird Indian/Turkish ones I have seen the bodies, diaphragms and pumping chamber are all the same, but what does differ from engine to engine is the operating lever. just to complicate matters it seems even "genuine" good quality 1.5 and, presumably, 1.8 pump now have a different operating lever, although they work fine.

 

The wrong level may either get bent if its movement and placement do not suit the eccentric on the camshaft, or simply not allow full strokes of the pump.

For the OP

 

I wrote this in another topic about tank cleaning.

•  

Posted August 23

On 23/08/2023 at 17:57, moiuk said:

My plan is to check a few easy things next time it happens.. the drive shaft still rotates by hand, and check the temperature of the parts when it shows itself..

 

If this doesn't narrow it down I'll look into the fuel which is a bit harder for me as I've not done that before.

 

Appreciate your input 🙂

 

Assuming a typical narrowboat fuel tank locations.

Accumulate a number of plastic milk cartons, 2 litres seem the most manageable.

Get a length of clear plastic hose of say about 3/8" diameter and push a "wand" made of copper pipe in the end and bend it slightly.

Put a milk bottle on the baseplate with the other handy and one beside/behind it.

Put the copper pipe into the fuel filler and onto the bottom of the tank.

 

Now the bit you need to get used to the taste.

 

Give the other end of the plastic pipe a good suck and put your finger over the end of the pipe in your mouth to seal it.

Put pipe end with finger over the milk carton and release your finger, push hoes into the milk bottle so the syphon you created starts to drain the tank

Sweep the wand all over the bottom of the tank, paying special attention to the tank bottom to side joint areas.

As each milk carton fills move, a new one to be filled.

Keep going until there are no more dark bits coming up with the fuel and until the fuel in the plastic hose is a nice clear red colour.

 

Once you get the bits together, it should all be doe in 15 minutes.

 

You can stop at any time by lifting the hose higher than the fuel level in the tank, and even come back when you have accumulated more milk cartons.

You can use a syphon pump or in some cases an oil change pump or a Pella extractor but a length of plastic pipe and copper pipe is cheaper.

 

If you let the milk cartons stand for a week, the clean fuel can be carefully poured off, leaving the water, emulsified fuel and dirt in the bottom.

Post some photos of what settled out.

 

 

Try to ensure the wand/copper pipe, gets into all the corners of the tank, if you can give the boat a good list it will help the water concentrate at the lowest point.

 

 

[magnetman]

Yes thats why I started my post with the words

"A bad lift pump does not mean a leak. It could be a fault with the diaphragm or a damaged arm. 

Or the valves. "

 

I think it could well be something to do with the arm/lever. 

 

 

 

 

[Mark R]

Sorry, just to confirm that the glass with the diesel in it has a deep glass bottom, that isn't diesel floating on water. I probably used the worst possible glass to show the diesel. Is the diesel in the bottle still classed as contaminated? I'm going to clean the tank tomorrow any way.

 

Edited September 4, 2023 by Mark R

[Tracy D'arth]

7 minutes ago, Mark R said:

Sorry, just to confirm that the glass with the diesel in it has a deep glass bottom, that isn't diesel floating on water.

I doesn't need to be, there is enough water in the diesel as it is!  Its heavily contaminated.

[Mark R]

Cheers Tracy, 

 

I'll get it removed tomorrow and clean the tank.

 

In response to Magnetman, I did check the fuel level and my stick showed it was about 5" from the bottom of the tank.

[Tony Brooks]

14 minutes ago, Mark R said:

Sorry, just to confirm that the glass with the diesel in it has a deep glass bottom, that isn't diesel floating on water. I probably used the worst possible glass to show the diesel. Is the diesel in the bottle still classed as contaminated? I'm going to clean the tank tomorrow any way.

 

 

Agree with Tracy and it might have bug now you say about the glass. keep draining until the diesel coming out is a nice bright red and in no way clouldy.

[Tracy D'arth]

Clean diesel looks like a good red wine, it should sparkle and be clear.

[Mark R]

I'm assuming you'd be talking about red diesel in that case.

 

[Tony Brooks]

5 minutes ago, Mark R said:

I'm assuming you'd be talking about red diesel in that case.

 

 

Yes, what most boaters use, but if it is DERV or a bio-fuel it should still be bright and clear, possibly with a yellow colour. It should not be cloudy unless you are in Southern Island, in which case it may be green, but then its use would be illegal in a pleasure boat.

[MtB]

1 hour ago, Tracy D'arth said:

Clean diesel looks like a good red wine, it should sparkle and be clear.

 

 

I'm a bit worried about what sort of wine you've been drinking if yours looks like diesel  ...

 

Good red wine is usually more opaque than diesel, I'd suggest. Redder too (if that's a word!)

 

 

[Tony Brooks]

3 minutes ago, MtB said:

 

 

I'm a bit worried about what sort of wine you've been drinking if yours looks like diesel  ...

 

Good red wine is usually more opaque than diesel, I'd suggest. Redder too (if that's a word!)

 

 

 

Should be more like a Rose's

[magnetman]

3 hours ago, Mark R said:

Cheers Tracy, 

 

I'll get it removed tomorrow and clean the tank.

 

In response to Magnetman, I did check the fuel level and my stick showed it was about 5" from the bottom of the tank.

5 inches of fuel in the tank is getting towards the dregs. 

 

Do you know how high up the take-off is? It should never be at the bottom of the tank for obvious reasons .

 

 

1 hour ago, Tony Brooks said:

 

Should be more like a Rose's

 

That would be green diesel

 

 

[Tony Brooks]

10 minutes ago, magnetman said:

5 inches of fuel in the tank is getting towards the dregs. 

 

Do you know how high up the take-off is? It should never be at the bottom of the tank for obvious reasons .

 

 

 

That would be green diesel

 

 

 

No - sweet pink summer wine.

[john.k]

We used to get free diesel at the refinery ,and it was so clear ,you could see things on the bottom of a 44 gallon drum full............anyhoo,back to the filter top.......the top bolt not only has a centre hole and cross drilling,but also should have a small steel ball inside ......the purpose of this is to prevent fuel being pulled back out of the tank when filters block ,and fed to the motor unfiltered .

[Mark R]

10 hours ago, magnetman said:

5 inches of fuel in the tank is getting towards the dregs. 

 

Do you know how high up the take-off is? It should never be at the bottom of the tank for obvious reasons.

 

 

 

 

 

I'll measure that today, I was assuming that the take off would be a couple of inches below the bottom. It'll be good to know such things.

 

Where's the best place for getting rid of contaminated diesel?

[Tony Brooks]

52 minutes ago, Mark R said:

 

I'll measure that today, I was assuming that the take off would be a couple of inches below the bottom. It'll be good to know such things.

 

Where's the best place for getting rid of contaminated diesel?

 

Let it stand in containers (plastic milk cartons) for several days/weeks and with a bit of luck it will separate with clear diesel at the top and the water and muck at the bottom. The clear stuff can be returned to the tank with some biocide, and the rest I would take to the waste oil place at your local tip.

 

In any case, I would use a strong dose of biocide in the tank once it has been cleaned.

 

I don't think that you will find any ball in the top bolt of any UK BMC 1.5 or 1.8 filter, you certainly do not have one and neither have any others I have seen. The return should be into the top of the tank, so unless you overfill it, it could only suck air, and how the pressure side of the lift pump can suck is beyond me. It must be an Australian thing. The only thing that is anything like that is the valve in the union where the return from the injection pump is connected to the filter.

[Tracy D'arth]

4 hours ago, john.k said:

the top bolt not only has a centre hole and cross drilling,but also should have a small steel ball inside ......the purpose of this is to prevent fuel being pulled back out of the tank when filters block ,and fed to the motor unfiltered .

Having a steel ball inside is just   er   balls. Never seen a BMC banjo with a non return valve.

[MtB]

4 hours ago, Tracy D'arth said:

Having a steel ball inside is just   er   balls. Never seen a BMC banjo with a non return valve.

 

Maybe they are fitted only to Australian engines, which have to run upside down. Obviously.