BMC 1.8 Odd revs increase, cause unknown.

[Tracy D'arth]

16 minutes ago, Bee said:

I only have two thoughts. 1) change the filter because its easy and 2) these things sometimes speed up just before they run out of fuel so I wonder if it is sucking a tiny bit of air from the filter or bleed screw from time to time. That's as far as go with these things - pumps frighten me.

 

1 hour ago, Tony Brooks said:

 

It certainly would not hurt given the price of the filter. The reason I have not suggested it is that I would expect Tracy to have considered that.

 

1 hour ago, David Schweizer said:

A lot of talk about dismantling various components, why don't you just change the fuel filter and see if that solves the problem. I have met several people who have had the same issue and resolved it by changing the fuel filter. My only concern about that diagnosis is that Tony Brooks has not suggested it.

I will get her to change the filter. I suspect it will not be so simple as this engine will rev up to its near maximum revs under load. She tells me that if the throttle is brutally opened with it in gear, the exhaust will pour black smoke until the revs settle and the acceleration stops so it is getting unlimited fuel. The prop is a big high performance wide blade Crowther, the way it shifts water is incredible.

[Tony Brooks]

That usually suggest over propping because BMCs are not known for pouring smoke out upon revving, unlike the old small Volvos. However, that does not explain the revving up.

[Tracy D'arth]

3 minutes ago, Tony Brooks said:

That usually suggest over propping because BMCs are not known for pouring smoke out upon revving, unlike the old small Volvos. However, that does not explain the revving up.

It is over-propped, the boat was built for the river Trent I believe. It was impressive when I had it in open water on the Severn for a week many years ago.

[Tony Brooks]

A further thought. The DPA pump alters the pump timing according to the pressure in the pump body, this is done to aid cold starting, but if the pressure in the body (transfer pump pressure) alters it may well alter the timing and cause a rev up or down on a steady throttle opening. But we are still back to transfer pump pressure.

[Tony Brooks]

Another thought. I am sure there is a pressure gauge connection on one end of the advance retard piston housing so if you have a suitable pressure gauge and adaptor you could rule out or rule in transfer pump pressure. I bet on the 1.8 it will be inaccessible though.

[Tracy D'arth]

11 minutes ago, Tony Brooks said:

Another thought. I am sure there is a pressure gauge connection on one end of the advance retard piston housing so if you have a suitable pressure gauge and adaptor you could rule out or rule in transfer pump pressure. I bet on the 1.8 it will be inaccessible though.

 

9 hours ago, Tony Brooks said:

A further thought. The DPA pump alters the pump timing according to the pressure in the pump body, this is done to aid cold starting, but if the pressure in the body (transfer pump pressure) alters it may well alter the timing and cause a rev up or down on a steady throttle opening. But we are still back to transfer pump pressure.

I'll go and have another look at it this week. I have a few pressure gauges, what pressures am I to expect?

Advance /retard could be the possibility but the periodic nature is odd. It could explain the raised tickover as a properly timed 1.8 will speed up slightly if it is then advanced slightly. My timing gauge has gone somewhere unfortunately, I probably lent it out and never got it back.

[Tony Brooks]

1 minute ago, Tracy D'arth said:

 

I'll go and have another look at it this week. I have a few pressure gauges, what pressures am I to expect?

Advance /retard could be the possibility but the periodic nature is odd. It could explain the raised tickover as a properly timed 1.8 will speed up slightly if it is then advanced slightly. My timing gauge has gone somewhere unfortunately, I probably lent it out and never got it back.

 

I am afraid that I don't have the pressure to hand, I am sure it will be in the CAV manual and if you use a company to overhaul injection stuff regularly then I would hope, as trade, they would tell you. Maybe it is in that Fuji yachts link I posted.

[Mad Harold]

A long shot.

I experienced similar but on an outboard.

The cause I found eventually was vibration acting on a rather loose throttle linkage.

The symptoms were an uncalled for increase in revs for about five or six seconds and then back to normal for a time, and then an increase again.It kept doing this ad infinitum.

Vibration was moving the loose throttle linkage just enough to increase revs, and with the increase in revs, there was less vibration (or a different frequency) and the revs would return to normal.

[Tracy D'arth]

1 minute ago, Mad Harold said:

A long shot.

I experienced similar but on an outboard.

The cause I found eventually was vibration acting on a rather loose throttle linkage.

The symptoms were an uncalled for increase in revs for about five or six seconds and then back to normal for a time, and then an increase again.It kept doing this ad infinitum.

Vibration was moving the loose throttle linkage just enough to increase revs, and with the increase in revs, there was less vibration (or a different frequency) and the revs would return to normal.

I investigated this possibly first, the return spring should always pull the cable back fully. I did think too that there could be excessive wear in the throttle spindle housing but it is not the case. Thanks for the thought.

[Tony Brooks]

I can't see any pressures in the Fuji manual, and it is for the mechanically governed DPA any way, but if the pressure in the advance retard unit or in the pump body (connect gauge to the body bleed screw)  alters and coincides with the revving up it will point to a fuel problem, particularly if it drops. It would not surprise me if the body pressure alters across the rev range (how else would a hydraulic governor know the engine speed).  I would take a set of speed and pressure readings before it played up to use as a baseline.

[Tracy D'arth]

On 20/08/2022 at 19:30, Bod said:

Temperature dependant.  Has any work been done on the cooling system?

Pipes moved, cables moved against or away from hot pipes/exhaust.

Thermostat changed, increased speed for a short time, thermostat opens and shuts in about the same time scale.

Random thoughts barking up the wrong tree......

 

Bod

Carry on barking, all suggestions accepted, thanks but none of the above. Solution to follow, I think.

[Tracy D'arth]

So after an extensive week of brow beating and hair tugging I visited the boat again determined to find the answer.

I took another injection pump, just in case, but it has a manual stop not a solenoid.

In the event it was not required.

 

Decided to start at the fuel tank. half full, no leaky pipes, no air getting sucked in. Lift pump working fine, holding suction on my finger over the inlet.

 

Dismantled the fuel filter. A small amount of fine dust in the bowl and on the top of the element, no water, no bug. Took the non-return valve off the return from the pump, not blocked and working.

Discovered that the "Banjo" union on the spill rail connection on the filter head to the tank return was a steel bolt that had been drilled and cross drilled. It was fine, no blockage. Blowing the return back to the tank was OK.

Dropped a new filter in anyway, bled the pipes and injection pump.

Fired up easily on all four. I ran it for half an hour tied up to get some load on it and warm it up when it started its performance again, raised tickover, spasmodic revving up. So no cigar.

 

I considered taking the valve assembly out of the transfer pump end of the pump as Tony suggested but as it lies sideways on the 1800 I didn't fancy trying to get all the bits and springs to seat back in properly.

 

Nearly gave up and started to remove the pump when I realised that the bottom of the body was wet with diesel. I had dried everything off after bleeding so it seemed that there was a slight leak somewhere. Even If I could not fix the odd running the leak needed fixing so that the boat could be moved.

 

Ragged all the pump and pipes off and set to with the blue tissue. The tiny leak was on the diamond plate that carries the return union. This was still tight, the locking wire and seal intact. But leaking it definitely was . I have a resealing pack for these pumps so I cut the wire off and removed the plate, two 8mm AF screws.

The gasket is rubber and this one had gone hard, the middle had swelled and curled up and was sticking into the pump body. I don't know what it was pressing on in there, I usually just give injection pumps to a specialist to sort out.

Replaced the gasket, nipped up the screws and bled the pump and injectors again. Fired up and ran the motor for an hour. Tick over back to its 550 rpm immediately and no sign of the revs increasing. Job done, finally. So what was in the pump that the gasket interfered with?

 

Relieved owner, even happier me!

 

A success after a lot of head scratching and difficult spanner twiddling in a confined space, I left totally knac*ered ( getting far too old for this sort of punishment ) but with a sense of achievement.  I hate being beaten by a mechanical fault.

 

Thanks to all who made some very good and logical suggestions, turned out to be a silly distorted gasket after all.

Edited August 27, 2022 by Tracy D'arth

[Tony Brooks]

2 minutes ago, Tracy D'arth said:

So after an extensive week of brow beating and hair tugging I visited the boat again determined to find the answer.

I took another injection pump, just in case, but it has a manual stop not a solenoid.

In the event it was not required.

 

Decided to start at the fuel tank. half full, no leaky pipes, no air getting sucked in. Lift pump working fine, holding suction on my finger over the inlet.

 

Dismantled the fuel filter. A small amount of fine dust in the bowl and on the top of the element, no water, no bug. Took the none return valve off the return from the pump, not blocked and working.

Discovered that the "Banjo" union on the spill rail connection on the filter head to the tank return was a steel bolt that had been drilled and cross drilled. It was fine, no blockage. Blowing the return back to the tank was OK.

Dropped a new filter in anyway, bled the pipes and injection pump.

Fired up easily on all four. I ran it for half an hour tied up to get some load on it and warm it up when it started its performance again, raised tickover, spasmodic revving up. So no cigar.

 

I considered taking the valve assembly out of the transfer pump end of the pump as Tony suggested but as it lies sideways on the 1800 I didn't fancy trying to get all the bits and springs to seat back in properly.

 

Nearly gave up and started to remove the pump when I realised that the bottom of the body was wet with diesel. I had dried everything off after bleeding so it seemed that there was a slight leak somewhere. Even If I could not fix the odd running the leak needed fixing so that the boat could be moved.

 

Ragged all the pump and pipes off and set to with the blue tissue. The tiny leak was on the diamond plate that carries the return union. This was still tight, the locking wire and seal intact. But leaking it definitely was . I have a resealing pack for these pumps so I cut the wire off and removed the plate, two 8mm AF screws.

The gasket is rubber and this one had gone hard, the middle had swelled and curled up and was sticking into the pump body. I don't know what it was pressing on in there, I usually just give injection pumps to a specialist to sort out.

Replaced the gasket, nipped up the screws and bled the pump and injectors again. Fired up and ran the motor for an hour. Tick over back to its 550 rpm immediately and no sign of the revs increasing. Job done, finally. So what was in the pump that the gasket interfered with?

 

Relieved owner, even happier me!

 

A success after a lot of head scratching and difficult spanner twiddling in a confined space, I left totally knac*ered ( getting far too old for this sort of punishment ) but with a sense of achievement.  I hate being beaten by a mechanical fault.

 

Thanks to all who made some very good and logical suggestions, turned out to be a silly distorted gasket after all.

 

Thanks for the feedback and pleased it seems to be sorted. I can't work out why a slight leak would do that unless it occasionally got to be a larger leak that slightly reduced the pressure in the body. The important thing is that it is another thing that may help others.

[Tracy D'arth]

I think the curly gasket was interfering with something inside the pump, the leak was small, not a constant drip, more an ooze.

[Tony Brooks]

Just now, Tracy D'arth said:

I think the curly gasket was interfering with something inside the pump, the leak was small, not a constant drip, more an ooze.

 

I can't think what, it is too far forward and well away from the governor and its inlet drilling. On the mechanical DPA I think it might be close to the centrifugal bob weights, but I think they would just chew up the gasket because they are large and engine driven.

[Tracy D'arth]

If the rubber was touching the bob weights, that would cause the bob weights to increase fuel flow? Seems logical. The rubber is very stiff, no edges that would catch on the weights but definitely sticking into the pump by about 12-16mm.

[Tony Brooks]

1 hour ago, Tracy D'arth said:

If the rubber was touching the bob weights, that would cause the bob weights to increase fuel flow? Seems logical. The rubber is very stiff, no edges that would catch on the weights but definitely sticking into the pump by about 12-16mm.

 

 

Hope I am not teaching egg sucking but:

 

No bob weights in the 1.8 injector pump unless someone has swapped it for the mechanical one as I have seen on a few 1.5s, but I have doubts there is enough space on a 1.8 to fit it. The governor on the 1.8 is the same as the majority of 1.5s.  It is a tiny little thing that hangs down from the bottom of the control turret. It just balances between the pressure in the pump body and the spring preloaded by the throttle spindle.

 

All there is in the space below the outlet is the pump spindle and possibly a circlip securing the splined drive to the rotor. Neither has anything to do with the governor. Diagram below.

 

 

 

 

[Tracy D'arth]

28 minutes ago, Tony Brooks said:

 

Hope I am not teaching egg sucking but:

 

No bob weights in the 1.8 injector pump unless someone has swapped it for the mechanical one as I have seen on a few 1.5s, but I have doubts there is enough space on a 1.8 to fit it. The governor on the 1.8 is the same as the majority of 1.5s.  It is a tiny little thing that hangs down from the bottom of the control turret. It just balances between the pressure in the pump body and the spring preloaded by the throttle spindle.

 

All there is in the space below the outlet is the pump spindle and possibly a circlip securing the splined drive to the rotor. Neither has anything to do with the governor. Diagram below.

 

 

 

 

Ah, the 1800 pump with solenoid stop is nothing like that, I cannot find a drawing of this pump.  There is no stop leaver and linkage. It will be a Sherpa pump.

I don't know what is in the hole behind the plate, I didn't look!  Too busy refitting with a new gasket and then on starting it I find it is now  working properly. To elated to worry!

[Mad Harold]

17 hours ago, Tracy D'arth said:

Ah, the 1800 pump with solenoid stop is nothing like that, I cannot find a drawing of this pump.  There is no stop leaver and linkage. It will be a Sherpa pump.

I don't know what is in the hole behind the plate, I didn't look!  Too busy refitting with a new gasket and then on starting it I find it is now  working properly. To elated to worry!

Goes to show that regardless of length of experience, there is always something new.

Glad you got it sorted.0