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BMC 1.5 won't stop - old problem resurfaced


Cattleya

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I have had this issue on and off for a few years now, most of the time my BMC engine runs without any issues but every so often it won't stop when I pull the manual stop lever.

 

The issue isn't anything to do with the cable as I've checked and the lever on the governor turret moves its full travel. Once it starts playing up it will continue to do so until after the engine has been left a few hours to go cold.

 

I'm guessing something has worn in the turret on top of the CAV pump, or maybe there is a problem in the CAV pump itself allowing fuel to leak past. When it plays up the engine will rev to about 1200rpm when the stop lever is pulled, normally tick over is about 600rpm. I'm certain the engine is not running on its oil when it does this as it does not rev uncontrolled, it just picks up to 1200rpm, plus the oil level remains the same.

 

I don't know much about how the CAV injector pump/governor works so am reluctant to take it to bits. How do I remove the pump from the engine so I can take it to a specialist? Does the engine have to be in a certain position to remove it? Will I mess up the timing by removing it? I'm trying to work out if I can DIY or if I need to pay a mechanic to remove and refit the pump.

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Assuming that your 1.5 has the normal injector pump, a few do not but the talk of a turret suggests it is normal.

 

Normally revving up is a sign of lack of fuel because the fuel pressure that is trying to close the governor valve drops so the spring (loaded by the throttle lever) trying to open the valve wins so more flue despite the lower pressure is delivered to the engine. Your symptoms do not sound like fuel starvation in the conventional sense.

 

When you operate the stop it should lift the governor valve into the no fuel position by mechanical means with no springs involved and although I fully believe you I would say your symptoms are impossible unless the top has fallen off the governors valve assembly but even then its doubtful.

 

Removing the pump is easy as is replacing it as long as the overhauls shop scribes the mounting flange properly.

 

All pipes and control cables off, take steps to keep dirt and dust out of pipes and holes.

 

Look at the triangular mounting flange. On one corner (top front think) you should see a line scribed on the pump flange and a movable pointer screwed to the engine "flange". Make sure they line up, if not adjust the pointer.

 

Undo the three mounting nuts (a thin socket and extension may be needed). and simply pull the pump away from the engine.

 

The drive has a master spline so whatever position the engine stops in you just have to turn the drive on the pump so the master spline lines up with the corresponding part of the drive in the engine and push the pump home. Then twist the pump on the elongated holes in the flange so the pointer and line align.

 

 

I think that you should get the pump overhauled and tested so you know its working well. As I said the symptoms make little sense to me.

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Thank you Tony, that doesn't sound too difficult to remove. I'm on a limited budget and I know how the marina engineers like to turn everything into an expensive invoice, so I will remove the pump and take it to be tested.

What has fallen off the top is a cover that was over one of the adjustment screws, this also had some sort of attachment that stopped the screw moving. I'm not sure if this has anything to do with my problem.

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There are three adjustment screws but you may only see two. ON older pumps its only two.

 

On the newer pumps you have two long vertical set screws, one a throttle stop that should be covered with an aluminium wired on cap to stop YOU twisting it and blowing up the engine and the other identical one without the cap is the idle adjustment screw that you can play with. The third one is part of the assembly of hexagons in the centre of the turret. This is the idle damper that stops the engine stalling as you throttle back. You should not need to touch this and it should not give these symptoms.

 

Older pumps have no throttle stop and the idle adjustment is by a screw with a spring on it that looks like a carburettor mixture screw.

 

Messing with the idle damper could allow it to stall when throttling back or could prevent the idle screw lowering the idle speed sufficiently. None of the screws should give the symptoms you describe.

 

 

 

 

If you observe absolute cleanliness you could try this. Disconnect the cables. Undo the two hexagon screws that secure the turret to the pump body and lift the while thing out. Most of the governor will be hanging down. Work the throttle and stop levers to make sure they are moving the governor valve. Using lint (hair/fibre) free cloth clean the valve and the little hole it sits in, swill in diesel. The reassemble.

 

If you pull the throttle and stop levers out of the turret once the two securing screws are out the governor valve should just fall out so you can see all of it but its a bit of a jiggle to get the levers back in correctly so I would not advise this.

Edited by Tony Brooks
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Thank you Tony.

I have been looking at how the DPA pump works and from what I can see there is a spring loaded valve connected to the throttle that moves up and down to control the flow of fuel, with the stop lever puling this up to stop the flow of fuel. Is it possible for fuel to leak past this in a worn pump?

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