[pointer]

After some work and new parts (starter motor, battery, headset and injectors) we'd managed to get our tractor running. Then it started conking out, and now become hard then impossible to start once again. When it first stopped starting, there was lots of fumes from the exhaust but it just couldn't quite click into life, but now there's relatively little white smoke when turning the engine over. We've bled the fuel system, fuel getting to all the injectors though noticeably less flow to the fourth than the other three. Fair to say we've reached the limits of our mechanical ability, and getting a bit frustrated! Any ideas?
I should add that the engine has also developed a more fundamental flaw, in that fuel (diesel and oil) is dripping down the bottom of the exhaust - but I don't think that should be preventing it starting?

[stufe35]

A few ideas to explore : 

Have you checked all the fuel pipe joints are tightened properly...could be air getting into the system somewhere.

When you turn the starter over you should get white smoke coming from the exhaust. This is unburnt fuel and demonstrates that fuel is getting through. If not you need to bleed/ look for why fuel isn't getting through.

Not forgetting the obvious one..is there fuel in the tank (plenty) ?

The fact your tractor stopped whilst running suggests a fuel starvation problem....have you changed the fuel filter(s)...depending what the tractor is there should be one or even two canister type ones (like an oil filter) also there will probably be a glass fuel sediment bowl.  Have you cleaned this ?  Sometimes there is a small gauze filter in the top of this that may need cleaning.   

Next there maybe a filter in the fuel tank where the out let is.  Best way to clear this is to disconnect the fuel pipe at the closest point possible to the tank out let and then blow air up the pipe into the tank using a compressor...or bike pump if you don't have one.

Finally a common problem can be the fuel lift pump. They have a rubber type diagphram in them that pumps the fuel, if this has a hole in it , it reduces or stops the flow. You can buy refurb kits with new seals etc. or a whole new pump isn't a great deal and is easy to fit on most tractors.

[pointer]

Many thanks for this Stu, much appreciated. We'll go through these tomorrow.
My only question is, if it was one of these issues, would we still be getting fuel flowing through well to the injectors (we haven't had the injectors off, just the nut above each one linking it to the fuel supply)? We get the fuel flowing through when using both the lift pump and the ignition.
Likewise, we are still getting some white smoke when trying to start, though not the suffocating clouds of it we used to get! This is getting us thinking it might be the actual injectors, even though they've just been reconditioned. Or would these symptoms still be consistent with some of the possibilities you mentioned?
thanks

[stufe35]

I don't think it will be your injectors.  If some fuel is getting through and you've had it running I'd say most likely fuel starvation.....most likely a blocked filter somewhere.

is the fuel tap switched on fully. .?

[stufe35]

Just another thought....you talked about the tractor stopping whilst running......what was the outdoor temperature when this happened ?  It been freezing a lot lately...did it stop because the diesel has started to freeze ?  Are you using winter grade diesel ?  If you are is it mixed with summer grade diesel which was already in the tank making it less effective.....this could be your tractor tank and/or your bulk tank if you have one.

[Rupert the bear]

You say new parts and mention " headset " what do you mean by that , valve gear, head gasket ?

[pointer]

Yes, head gasket.

[Rupert the bear]

when you replaced the cylinder head did you check the valve clearances ?  Have you been able to trace the source of the fuel/oil  dripping from the exhaust ? I would suspect a leak around the head gasket area and possibly a reduction in compression.
What make tractor is it ?

[pointer]

Yes, valve clearances were checked.
No, I don't know where the leak is coming from. It's a David Brown 995.
How would I check for lack of compression? thanks

[mab]

if you've been trying to start for a bit without success then there will be fuel in the exhaust - as to the oil? head gasket has to be considered... when it was running, was the exhaust clean or was there 'blue' smoke?

It may be worth re-checking valve clearances just to rule it out - it's relatively quick & easy and doesn't cost anything - and maybe somthing's settled since they were set;  funny things can happen when a head gasket is done.

It seems improbable that all four injectors should go belly up just after reconditioning! so once you've ruled out all other fuel issues I'd suspect the injection pump - but as that's £££ to sort out I'd really make sure of everything else first.

Have you checked the tiny gauze filter in the inlet to the injection pump? it shouldn't ever block as it's downstream of the filters, but...
It is diesel coming out of the injector pipes? not water?

As for compression testing - I've never done it and don't have a suitable tester but you fit it in place of one of the injectors I believe - try asking around if someone has one to borrow unless you really want to buy one.

[Rupert the bear]

if you've been trying to start for a bit without success then there will be fuel in the exhaust - as to the oil? head gasket has to be considered... when it was running, was the exhaust clean or was there 'blue' smoke?

It may be worth re-checking valve clearances just to rule it out - it's relatively quick & easy and doesn't cost anything - and maybe somthing's settled since they were set;  funny things can happen when a head gasket is done.

It seems improbable that all four injectors should go belly up just after reconditioning! so once you've ruled out all other fuel issues I'd suspect the injection pump - but as that's £££ to sort out I'd really make sure of everything else first.

Have you checked the tiny gauze filter in the inlet to the injection pump? it shouldn't ever block as it's downstream of the filters, but...
It is diesel coming out of the injector pipes? not water?

As for compression testing - I've never done it and don't have a suitable tester but you fit it in place of one of the injectors I believe - try asking around if someone has one to borrow unless you really want to buy one.

Wot he said ..   
Have a good look at the gasket just in case.
Is the engine is turning fast enough to start ?
In addition I would be sure that the fuel system from start to finish  is checked and clean
And finally  I've left this to last, as with My old 990 I left this to last    just have a look at the stop control on the injection pump 

[pointer]

OK, so for some reason it started first turn this evening, drove it about 400m from shed and back. While manoeuvring back into shed, engine cut out, water everywhere on engine and radiator. Take it that's the head gasket blown? And if so, any idea why?

[Rupert the bear]

started and run for a while suggests as mab said  "tiny gauze filter" or possibly as stufe35 mentioned fuel waxing, I take it its got warmer ? my money on filter (s) choking ,
When its day light Have a good look around the engine, have the core plugs popped or corroded through ? Saying water every where suggests water blown backwards by the engine  fan has water pump gasket failed , possible if its the leather type .Hoses and rad check for leaks.

[pointer]

I very much appreciate all the suggestions, thanks.
Rupert, is core plugs the same as frost plugs, as someone else had also suggested that? Will check them tomorrow in daylight, once I figure out what and where they are. If that is what's happened, what do I do next?
Will also try to check pump filter as advised.
Water was on radiator and leaking out from rocker cover, with more water under the rocker cover.
It's stayed pretty cold here the last few days, only about 3 degrees today.

[Rupert the bear]

Core plugs = frost plugs if popped / corroded replace if distorted if still in shape tap them back in with soft hammer or block of wood

Water under rocker cover, and on Rad , Hmm , is is defiantly out of the rocker cover ? ( and then I think to myself if anything s coming out of the rockreer cover whats happened to the gasket ? )  is so then I would  check head gasket again and examine head for any damage and check block for any cracks ( this could be a loss of compression path, crack tight when cold opening when warmed, unlikley )(. Whats the engine oil like? hopefully no sight of water contamination.
before that check the thermostat cover/ gasket /top hose , water is terrible for ending up away from where it emerges ( rad and hose leaks esp as fan blows water backwards )
Do you have a workshop manual ?
dont forget the fuel line filters, leaving it dead and comingback later for it to run a while  is a symptom of intermittand blockage
Ive tried to make this comprehensible but suffering from hard of thinking thanks to nurse and her mashoosive needle