Idle stabilisation damper screw

[Lochwarden]

My 1.5 BMC is idling to fast. The idle stabilisation damper screw doesn’t have a locknut on it, and is screwed down tight, presumably by a previous owner. The last time I bled the system after a filter change, I followed the manual and slightly undid the damper screw as well as the bleed screw on the side of the pump. I’ve just tried loosening the damper screw off slightly to try and lower the idle speed but fuel leaks out. It seems the thread has also gone as the nut now will not tighten down, so have temporarily wrapped a small piece of PTFE tape around the top

of the thread so it seals. The damper screw also doesn’t look like the one in the manual as it doesn’t have a pointed end, mine is flat with a hole in the middle. Can I remove just the governor housing to see what’s going on inside?

[Tony Brooks]

The pointed end is, in fact, a small spring-loaded pin, so you need to source the whole thing.

 

All you will find inside the governor housing is a "dangling" spring-loaded governor valve, nothing for you in there.

 

If it is not leaking and as long as the engine does not stall when reducing the revs I would leave well alone, not all DPA pumps for 1.5s had idle stabilisation dampers fitted.

 

 

[Tracy D'arth]

53 minutes ago, Lochwarden said:

My 1.5 BMC is idling to fast. The idle stabilisation damper screw doesn’t have a locknut on it, and is screwed down tight, presumably by a previous owner. The last time I bled the system after a filter change, I followed the manual and slightly undid the damper screw as well as the bleed screw on the side of the pump. I’ve just tried loosening the damper screw off slightly to try and lower the idle speed but fuel leaks out. It seems the thread has also gone as the nut now will not tighten down, so have temporarily wrapped a small piece of PTFE tape around the top

of the thread so it seals. The damper screw also doesn’t look like the one in the manual as it doesn’t have a pointed end, mine is flat with a hole in the middle. Can I remove just the governor housing to see what’s going on inside?

 The end is missing off the adjuster. I don't think that the lack of the adjuster on what is really only an anti stall device is the reason for a higher than normal tick-over speed. I have seen many of these pumps with the screws badly adjusted and most owners don't know how to adjust them anyway.

Edited September 17, 2023 by Tracy D'arth

[Lochwarden]

2 minutes ago, Tony Brooks said:

The pointed end is, in fact, a small spring-loaded pin, so you need to source the whole thing.

 

All you will find inside the governor housing is a "dangling" spring-loaded governor valve, nothing for you in there.

 

If it is not leaking and as long as the engine does not stall when reducing the revs I would leave well alone, not all DPA pumps for 1.5s had idle stabilisation dampers fitted.

 

 

Thanks Tony. The issue I have though is the high idle, makes locks and mooring up difficult. Would I be right in saying there’s a gauze filter on the inlet to the injection pump that if blocked would cause the engine to rev higher? 

2 minutes ago, Tracy D'arth said:

 The end is missing off the adjuster. I don't think that the lack of the adjuster on what is really only an anti stall device is the reason for a higher than normal tick-over speed. I have seen many of these pumps with the screws badly adjusted and most owners don't know how to adjust them anyway.

So I should be looking elsewhere for the cause of the high tick over D’ya think? 

[Tony Brooks]

1 hour ago, Lochwarden said:

Thanks Tony. The issue I have though is the high idle, makes locks and mooring up difficult. Would I be right in saying there’s a gauze filter on the inlet to the injection pump that if blocked would cause the engine to rev higher? 

So I should be looking elsewhere for the cause of the high tick over D’ya think? 

1. Unlikely at tickover. That would more likely cause a loss of maximum speed and power.

 

2. You have an idle speed adjuster screw on one side of the throttle lever on the pump, adjust it,

[magnetman]

I believe this is one of those things you don't mess with. 

 

I've got a pair of 1.5s on one of my boats which I did have to bleed at one stage but don't recall needing to fiddle with that bit. 

 

 

[Tony Brooks]

3 minutes ago, magnetman said:

I believe this is one of those things you don't mess with. 

 

I've got a pair of 1.5s on one of my boats which I did have to bleed at one stage but don't recall needing to fiddle with that bit. 

 

 

 

Normally you do not, despite what the manual says. Just use the bleed screw on the side of the body.

[Lochwarden]

4 hours ago, Tony Brooks said:

 

Normally you do not, despite what the manual says. Just use the bleed screw on the side of the body.

Yes, I was following the manual! You live and learn.

[Tony Brooks]

I just realised that the images do not show a typical 1.5 damper. Usually, but not universally, the damper screw has a bleed screw set into it.

[magnetman]

It seems like the original one might have been lost as the OP used the words "The idle stabilisation damper screw doesn’t have a locknut on it, and is screwed down tight, presumably by a previous owner."

 

Green is an interesting colour - has the engine been overhauled with a tin of paint at some stage? 

 

Is it just that someone has fitted the wrong part to an engine which was being rebuilt?

 

 

 

 

Is it meant to be this? 

 

https://www.charnleys.com/part/leyland_heavy/17h2484/screw-assembly-vent

 

[Tracy D'arth]

I don't think it is. The proper part has a pin that sticks out of the end into the governor housing which stops the governor from shutting down completely at idle, anti stall.

[Tony Brooks]

10 minutes ago, magnetman said:

It seems like the original one might have been lost as the OP used the words "The idle stabilisation damper screw doesn’t have a locknut on it, and is screwed down tight, presumably by a previous owner."

 

Green is an interesting colour - has the engine been overhauled with a tin of paint at some stage? 

 

Is it just that someone has fitted the wrong part to an engine which was being rebuilt?

 

 

 

 

Is it meant to be this? 

 

https://www.charnleys.com/part/leyland_heavy/17h2484/screw-assembly-vent

 

 

That looks like the bleed point in the body of the pump.

 

We painted all our engines green when on the fleet, and about that shade as well. The college training engines were also painted green. I don't think the colour is of much importance in this case.

Edited September 18, 2023 by Tony Brooks

[Lochwarden]

1 hour ago, magnetman said:

It seems like the original one might have been lost as the OP used the words "The idle stabilisation damper screw doesn’t have a locknut on it, and is screwed down tight, presumably by a previous owner."

 

Green is an interesting colour - has the engine been overhauled with a tin of paint at some stage? 

 

Is it just that someone has fitted the wrong part to an engine which was being rebuilt?

 

 

 

 

Is it meant to be this? 

 

https://www.charnleys.com/part/leyland_heavy/17h2484/screw-assembly-vent

 

Pretty sure that’s not the part I need, but thanks anyway. 

[Tony Brooks]

You may not need a new part to solve your high idle speed. There is an adjusting screw on the top of the pump, but if the cable is maladjusted it might prevent the lever touching the stop screw.

 

Locate the pair of screws 70 &  73 on your diagrams and work out which one stops the throttle lever as you drop to idle.

Get the engine warm

Remove the control cable from the lever and hold the lever against the idle adjusting screw.

Adjust screw to give the desired idle and tighten the locknut.

Adjust the cable so with the throttle held against the stop the fitting just drops into the hole in the lever.

 

I note that the cable adjusting locknut is loose, so someone has been at it before.

 

Only worry about the damper if you can't get the idle you want or if it stalls upon return to idle.  The screw you have at present can only prevent the governor valve rising, so limiting top speed and power.

[Lochwarden]

24 minutes ago, Tony Brooks said:

You may not need a new part to solve your high idle speed. There is an adjusting screw on the top of the pump, but if the cable is maladjusted it might prevent the lever touching the stop screw.

 

Locate the pair of screws 70 &  73 on your diagrams and work out which one stops the throttle lever as you drop to idle.

Get the engine warm

Remove the control cable from the lever and hold the lever against the idle adjusting screw.

Adjust screw to give the desired idle and tighten the locknut.

Adjust the cable so with the throttle held against the stop the fitting just drops into the hole in the lever.

 

I note that the cable adjusting locknut is loose, so someone has been at it before.

 

Only worry about the damper if you can't get the idle you want or if it stalls upon return to idle.  The screw you have at present can only prevent the governor valve rising, so limiting top speed and power.

Thank you Tony, that’s exactly what I’ve just started to do. I’ve released the throttle cable so it’s completely slack, started her up and she’s revving quite hard. Not happy running her that fast from cold. I will adjust the idling stop screw as you’ve suggested and hope I can lower the revs. The idle screw also has no locknut on it so someone in the past has obviously had a play with it. So would you know, is it anti-clockwise or clockwise to try and lower the engine revs? 

42 minutes ago, Tony Brooks said:

You may not need a new part to solve your high idle speed. There is an adjusting screw on the top of the pump, but if the cable is maladjusted it might prevent the lever touching the stop screw.

 

Locate the pair of screws 70 &  73 on your diagrams and work out which one stops the throttle lever as you drop to idle.

Get the engine warm

Remove the control cable from the lever and hold the lever against the idle adjusting screw.

Adjust screw to give the desired idle and tighten the locknut.

Adjust the cable so with the throttle held against the stop the fitting just drops into the hole in the lever.

 

I note that the cable adjusting locknut is loose, so someone has been at it before.

 

Only worry about the damper if you can't get the idle you want or if it stalls upon return to idle.  The screw you have at present can only prevent the governor valve rising, so limiting top speed and power.

So I’ve adjusted the idle screw right off and it’s made no difference to the engine revs. It’s more than a fast idle, it’s revving pretty hard, nervously so. Any ideas? 

[Tony Brooks]

9 minutes ago, Lochwarden said:

Thank you Tony, that’s exactly what I’ve just started to do. I’ve released the throttle cable so it’s completely slack, started her up and she’s revving quite hard. Not happy running her that fast from cold. I will adjust the idling stop screw as you’ve suggested and hope I can lower the revs. The idle screw also has no locknut on it so someone in the past has obviously had a play with it. So would you know, is it anti-clockwise or clockwise to try and lower the engine revs? 

 

Sorry, no, I don't know. Once you give it a twiddle it is obvious if it slows down or revs up. Looking at your diagram, I think you unscrew it to slow the revs, but your photo seems to show something very odd about the screw. For one thing, I have never seen one with a locking washer under the lock nut.

 

If you know which way the cable moves to slow the engine, it is easy enough to move the throttle to see which of the two screws limits its movement. They are just long set screws, so nothing out of the ordinary.

 

Don't mess with the other screw, it limits the top speed but as it has lost it aluminium tubular anti-tamper cover I expect that has been got at.

[Lochwarden]

4 minutes ago, Tony Brooks said:

 

Sorry, no, I don't know. Once you give it a twiddle it is obvious if it slows down or revs up. Looking at your diagram, I think you unscrew it to slow the revs, but your photo seems to show something very odd about the screw. For one thing, I have never seen one with a locking washer under the lock nut.

 

If you know which way the cable moves to slow the engine, it is easy enough to move the throttle to see which of the two screws limits its movement. They are just long set screws, so nothing out of the ordinary.

 

Don't mess with the other screw, it limits the top speed but as it has lost it aluminium tubular anti-tamper cover I expect that has been got at.

Anti clockwise to slow the idle down, but it’s made no difference to the engine speed, so can only assume it’s a problem elsewhere within the fuel system. I still suspect the idle stabilisation screw is the culprit, as it was fine up until the point where I removed it and discovered the thread was knackered and will now not screw down without plumbers tape on the thread. Thanks for you help though. 

[Tony Brooks]

If the remains of the damper screw is bearing down on the governor, then it may refuse to idle. So can you find a longer set screw that you can put a lock nut on so you can adjust it. It may be easier than locating a new damper screw.

[Lochwarden]

20 minutes ago, Tony Brooks said:

If the remains of the damper screw is bearing down on the governor, then it may refuse to idle. So can you find a longer set screw that you can put a lock nut on so you can adjust it. It may be easier than locating a new 

22 minutes ago, Tony Brooks said:

If the remains of the damper screw is bearing down on the governor, then it may refuse to idle. So can you find a longer set screw that you can put a lock nut on so you can adjust it. It may be easier than locating a new damper screw.

That’s probably my next move. That’s why I was asking whether taking the governor housing off to have a look was a good idea, see if anything is obviously amiss in there? I don’t want to make matters worse though. Although at the moment it’s revving too fast for me to get off the river bank anyway. 

52 minutes ago, Lochwarden said:

 

I know you suggested leaving the governor body alone, but is it possible that something is jammed inside causing the high revs? Is there anything I need to be aware of in removing the governor body? Thank you 

[Tony Brooks]

1 hour ago, Lochwarden said:

I know you suggested leaving the governor body alone, but is it possible that something is jammed inside causing the high revs? Is there anything I need to be aware of in removing the governor body? Thank you 

 

Only extreme cleanliness and using lint free cloths for cleaning. Dont pull the throttle or stop leavers out of the body, otherwise the governor assembly will drop out.

 

Having been through a load of CAV bumph, I feel all you need to do for now is to loosen the damper screw, even though it may well leak. See it that allows the revs to reduce.

 

I am not clear as to if the damaged thread is in the aluminium housing, the screw, or both. If the body is OK then while you try to locate a proper damper screw, try a set screw that is a bit longer so you can fit a lock nut and tighten it in the required position.

[Lochwarden]

14 minutes ago, Tony Brooks said:

 

Only extreme cleanliness and using lint free cloths for cleaning. Dont pull the throttle or stop leavers out of the body, otherwise the governor assembly will drop out.

 

Having been through a load of CAV bumph, I feel all you need to do for now is to loosen the damper screw, even though it may well leak. See it that allows the revs to reduce.

 

I am not clear as to if the damaged thread is in the aluminium housing, the screw, or both. If the body is OK then while you try to locate a proper damper screw, try a set screw that is a bit longer so you can fit a lock nut and tighten it in the required position.

Thanks Tony, your input is much appreciated. Unfortunately even with the damper screw out it is still revving very high. If the small filter underneath the hexagon on the pump is partially blocked, could that cause it to rev high, as the pump tries to compensate for reduced fuel flow? I’m pretty good mechanically but have very limited knowledge of how this fuel pump operates. I only have you guys, and the manual that came with the boat, which as I’ve found out isn’t always correct! 

[Tony Brooks]

Yes, it could, but it would be far more likely to do it when you want high speed or power because only then would a limited flow reduce the pressure in the pump body. By all means take the big hexagon out of the pump end plate but beware of flying springs, small plastic parts and observe extreme clenliness.

 

 

These pumps are simple, but with some high precision parts, but you are unlikely to get near them

 

Briefly, fuel enters the input in the end plate and into a vane type transfer pump. The filter you talk about is under the large hexagon that the inlet pipe is screwed onto. the transfer pump boosts the fuel pressure according to engine speed, but the pressure is controlled to a degree by the regulating valve that is also mixed up with that filter. The regulating valve also moves to make bleeding easier.

 

I think there are two springs associated with the regulating valve, so if you take the filter out, not only observe extreme cleanliness, but also beware of flying springs and little plastic parts.

 

The transfer pump pressurises the pump body and acts upon the governor valve. When you open the throttle, you preload a spring that tries to push the governor valve down towards maximum fuel, while fuel pressure tries to push it up towards no fuel. The position of the governor valve is balanced between the spring and fuel pressure. so the size of the orifice in the base of the valve can vary according to fuel and spring pressure. the larger the orifice the more fuel it can pass in a given time.

 

A hollow rotating shaft with a number of cross drillings rotates at half engine speed so when a cross drilling aligns with the governor valve orifice fuel can pass into the hollow shaft and from there into an opposed pair of pumping chambers pushing the plungers apart. How far apart they move depends upon the volume of fuel the governor allows into the cross drilling.

 

These plungers and chambers rotate a part of the hollow shaft, but within an internal cam ring so as the plungers align with the cam lobes they are pushed inwards pressurising the fuel in the hollow shaft and at the sometime another cross drilling aligns with one of a set of ports that connect to the injector pipe connections, so fuel is passed to the injector.

 

The shaft turn a little more so the original cross drilling aligns with the governor valve orifice so the plungers get recharged with fuel.

 

You will find illustrations etc. on my website (tb-training.co.uk) in the Articles section under Diesel fuel systems (BT).

 

PS Make sure the soft washer on that large hexagon are still soft and in good condition, the transfer pump just might be sucking air as well as fuel.

[Lochwarden]

17 minutes ago, Tony Brooks said:

Yes, it could, but it would be far more likely to do it when you want high speed or power because only then would a limited flow reduce the pressure in the pump body. By all means take the big hexagon out of the pump end plate but beware of flying springs, small plastic parts and observe extreme clenliness.

 

 

These pumps are simple, but with some high precision parts, but you are unlikely to get near them

 

Briefly, fuel enters the input in the end plate and into a vane type transfer pump. The filter you talk about is under the large hexagon that the inlet pipe is screwed onto. the transfer pump boosts the fuel pressure according to engine speed, but the pressure is controlled to a degree by the regulating valve that is also mixed up with that filter. The regulating valve also moves to make bleeding easier.

 

I think there are two springs associated with the regulating valve, so if you take the filter out, not only observe extreme cleanliness, but also beware of flying springs and little plastic parts.

 

The transfer pump pressurises the pump body and acts upon the governor valve. When you open the throttle, you preload a spring that tries to push the governor valve down towards maximum fuel, while fuel pressure tries to push it up towards no fuel. The position of the governor valve is balanced between the spring and fuel pressure. so the size of the orifice in the base of the valve can vary according to fuel and spring pressure. the larger the orifice the more fuel it can pass in a given time.

 

A hollow rotating shaft with a number of cross drillings rotates at half engine speed so when a cross drilling aligns with the governor valve orifice fuel can pass into the hollow shaft and from there into an opposed pair of pumping chambers pushing the plungers apart. How far apart they move depends upon the volume of fuel the governor allows into the cross drilling.

 

These plungers and chambers rotate a part of the hollow shaft, but within an internal cam ring so as the plungers align with the cam lobes they are pushed inwards pressurising the fuel in the hollow shaft and at the sometime another cross drilling aligns with one of a set of ports that connect to the injector pipe connections, so fuel is passed to the injector.

 

The shaft turn a little more so the original cross drilling aligns with the governor valve orifice so the plungers get recharged with fuel.

 

You will find illustrations etc. on my website (tb-training.co.uk) in the Articles section under Diesel fuel systems (BT).

 

Thank you for that explanation Tony, very much appreciated. I will check out your website. Thanks again.