Turning off the day-tank tap.

[MoominPapa]

Last night, contrary to my usual practice, I turned off the tap on the bottom of the diesel day tank for the Lister. Usually, the FR2 starts right on the button, but this morning I had to lean on the starter for a minute or so before is would catch. (Yes, I did turn the tap back on first).

 

Clearly, the diesel system is losing prime somewhere, but I'm not sure where. Could this be an indication that the injectors are dribbling when the engine is off? It may be my imagination, but the usual start-up cloud of black smoke was less today also, maybe indicating no excess diesel in the cylinders.

 

This is a pure gravity-fed system, with standard Lister style unit-CAV injection pumps, one for each cylinder. There are no obvious diesel leaks from low or high pressure pipework.

 

Since the rising-oil-level problem I was trying to diagnose by turning off the tap seems not to exist, I can solve the problem just by not turning off the day tank, but I'm interested to know what the explanation is.

 

MP.

[dcruk]

A few thoughts on your problem MP,

I would have thought it more likely that one or both pumps are leaking into the crankcase , though I'm not specifically familiar with FR's , the injectors have a set pressure of 180 bar (www.oldengine.org) so if one was dribling I would expect the engine to miss or run rough. The delay in firing would most likely be the pumps trying to fill back up and getting rid of the air . Might be worth taking the pumps off after the engine has been stood overnight and see if they are wet on the bottom ( with the day tank turned on). If either are wet with diesel then you need to get them sorted and change the engine oil too. I'm sure there are some Lister gurus around on here who can give you chapter and verse , hth, Dave

[jake_crew]

After a days running, the injectors and connected pipework will be hot, along with the fuel they contain.

 

As these cool, the fuel will shrink (much more than metal) - so if you turn off the feed from the day tank, you'll create a partial vacuum in the feed pipes. This might draw some air in through a connection and create an air-lock, air gases being smaller molecules than cetane, even though there was no sign of a fuel leak.

 

ed for spleling & clarity

Edited August 2, 2009 by jake_crew

[MoominPapa]

Thanks for the suggestions. I'm pretty sure that diesel is not getting into the oil in significant amounts. It's very difficult to get an accurate level because the engine is dry sump. If you run it for half an hour and then check the oil level it's much lower then if you run it all day. A thoroughly hot engine with hot oil scavenges much faster, and more of the oil ends up in the tank at shut down. I think that's the cause of the initial increase I saw now we're out and doing long days. Over subsequent days the level has not gone up significantly more. As the engine has 25 litres of oil in it, a small amount of diesel is not a worry.

 

The cooling/contracting suggestion is a good one. I'll try turning the tap off after the engine has cooled and see if I get the same effect. If so I guess I need to look for a small leak in the high pressure system.

 

 

Cheers,

 

MP.

[MoominPapa]

Time to revive this old thread. Whilst we were out, I never did get to the bottom of this.

 

I did find out that measuring the total oil quantity by looking at the level in the oil tank is hopeless. The amount of oil left in the engine (rather than returned to the tank) after shut-down is very variable, and oil in the tank tends to drain into the engine by gravity over time whilst the engine is shut down. Is suspect that the most reliable level is to be had with the engine hot and running - I'm still experimenting with that.

 

Having despaired at getting an answer that way, I've spent some cash on getting a sample of the oil analysed at a lab. The results have just come back, and the oil is over 6% diesel. Ooops. So it looks like I do have an internal diesel leak, but it's not obvious.

 

I've checked the high-pressure pipes and unions and there's nothing obvious there, similarly the leak-off pipework and feed pipes to the injector pumps. I looked at the bottom of the injector pumps - thanks dcruk - Mr Lister provides little inspection doors which make this easy. Nothing there as far as I can see (but of course it's all covered in engine oil.)

 

The one place where there is some free diesel is the outside of the injector pumps themselves. As far as I see, this must have some from either the bleed screw, the screw which locks the inards in place, or the delivery valve holder. As the diesel covers the pumps to the top, above the two screws, I'm wondering about delivery-valve holder. How is that sealed? the drawings I have don't show any sort of seal or copper-washer between the shoulder in the holder and the top face of the pump, but there is, I think something deep inside between the bottom of the holder and the delivery-valve seat. Could that be the problem? Is it worth undoing these and inspecting?

 

 

Any advice gratefully accepted.

 

MP. (newbie diesel fitter)

[koukouvagia]

After a days running, the injectors and connected pipework will be hot, along with the fuel they contain.

 

As these cool, the fuel will shrink (much more than metal) - so if you turn off the feed from the day tank, you'll create a partial vacuum in the feed pipes. This might draw some air in through a connection and create an air-lock, air gases being smaller molecules than cetane, even though there was no sign of a fuel leak.

 

ed for spleling & clarity

 

That's fascinating. I'd never thought about that. This may explain why Kelvin recommends that you leave the injector tommy bars loosened off when you stop.

[MoominPapa]

Time for an update on the saga.

 

The reason why I could never get a reliable oil-level from the tank became clear whilst the engine was left unused for a couple of weeks when we got back to base. During that time the entire contents of the oil tank (at least 25 litres) drained into the engine, filling the crankcase to main-bearing level and then running out of the crankshaft oil seal and filling the oil tray underneath to a fairly deep level too. There is a check-valve in the line between the oil pump and engine which is supposed to stop this, and it obviously wasn't working, possibly partly because the oil has been thinned by diesel. I've now removed the check valve, (ably assisted by Mr P Bear, of this parish) ground the seats and re-installed it.

 

I've pumped out all the oil/diesel mixture from the all the places it's got to, and ended up with about 35 litres. As it started out as 25 litres of oil, there's a fair amount of diesel in there!

 

This weekend I put new oil in, and started the engine. Carefully checking round, I've found a crack in a copper pipe from an injector leak-off port which is leaking steadily. All I have to do is get a new pipe made up, and the problem is solved (I hope!)

 

Incidentally, according to Peter Thompson, Listers can survive very high oil dilution without problems. The oil analysis came back with low wear levels (ie bearing material in the oil) so it looks like I've got away without knackering any bearings. (Touch wood).

 

MP.