The Fordson Tractor Pages Forum

1962 Super Dexta, 10,000 hours, 4838 injector pump.
Well we spent the weekend replacing the rings - you may know but if not, the injector bolts are also head bolts (that wasted half an hour) - so compression now exists. Trouble is, the engine runs only a little better. I suppose we should have checked first but we knew the compression was very low...
Anyway, having checked filter and fuel flow, no problem, we investigated the injector feeds. Rather a weak spurt on cranking - but it would build up pressure and spurt if I put my fingure over it. No 1 weakest. Then we removed injectors as a bank. By coincidence I blew into each through the inlet and no 1 injector blew straight through to the leakoff pipe. To me that means it's faulty.
(I have refrained from saying that we could start her only with a little Bradex).
The engine runs on two cylinders now, probably as before. I had the option of swapping for another bank of injectors from my '64 NPSD and it made little diference, maybe firing on 2 1/2. Power was poor and below about 1200rpm, if load was applied to sow the engine, it would not pick up. Even dipping the clutch again wouldn't help - the engine would die and not restart normally. Seems to me like fuel starvation.

So please help - is my diagnosis of the faulty injector correct? How strong should the spray be from the injector pump pipes? Are the injector nozzles the same for all Dextas?
I have read that the holes on the NPSD with 4696 pump are smaller than the 4838 minimec and earlier pumps. Is this true?

Rob

From what you say it would appear that the No. 1 injector is definetly faulty.

The symtoms that you desribe certainly suggest fuel starvation. Have you checked to see if there is a strainer fitted to the fuel tap inside the tank? Have you examined the lift pump for debris?

With the injectors removed from the engine and connected to the pipes so that they are pointing away from any one or anything, if you then turn the engine over with the starter motor a good injector will atomise the fuel and make a “farting” noise. A poor injector will not atomise the fuel which will emerge as jet.

I MUST EMPHASISE THAT YOU MUST KEEP ALL PARTS OF YOUR BODY AWAY FROM THE SPRAY FROM THE INJECTORS, WHICH IS CAPABLE OF PENETRATING HUMAN FLESH AND CAN CAUSE SEPTACEMIA.

If you remove the leakoff pipe from the injectors it is possible to insert a small diameter rod throught the top of the injector onto the top of the needle, if you place your finger on the top of the rod when the engine is running you can feel whether or not the needle is lifting.

Another method is to pinch the injector pipes between your finger and thumb when the engine is running and you should be able to feel a pulse as the injector opens and closes if the injector is in reasonable condition.

Even if the injectors have been fitted with the wrong nozzles it shouldn't stop the engine from starting and you have similar problems with both sets

Considering that the engine has run for 10,000 hours it is more than likely that the injection pump is in need of an overhaul, in which case don't be tempted to strip it down yourself as specialised equipment is required to recalibrate it correctly. I would also recommend that the injector nozzles are renewed.

Gerald

Thanks Gerald
The smell and feel of diesel may well be the death of me!
I have not checked the lift pump for debris, I will do, but the flow to it is good so whatever might lurk in the tank isn't restrictive. Is it possible to repair number one injector? I'm assuming it's a spring thing but I can only imagine that the spring has shattered which seems unlikely.

Rob

I would get your injectors and fuel pump to a diesel specialist for a check and refurb as necessary. I go to Peter Strong nr Reading. Very helpful guy and loves old stuff.

Ben
I have already emailed Peter Strong and await his reply but we tested only the manual lever on the lift pump so i am hoping that it may be full of rubbish - the main filter was after all - and some may have gone past. I don't really want to remove the injector pump until everything else is tested. I have visions of timing woes...
Rob

Leakage from the injector leak off is usually due to a worn needle or leakage between the faces of the injector body and the nozzle, without stripping the injector down it is is impossible to know. If the spring was broken you would have had leakage from the nozzle itself. To recondition the injectors it is usual to fit replacement nozzles and then adjust the spring so that the injector opens or atomises at 160 bar.

Your mention of timing the pump leads me to ask if you have checked the pump timing, there is a clear guide in the workshop manual. If you do have to remove the pump and are worried about the timing when replacing the pump, I suggest that you turn the engine so that the mark on the flywheel (26 degrees for a SD) at No. 1 TDC coincides with the notch in the housing, then remove the pump. If you leave the engine in this position until the pump is returned you know that the engine is in the correct position if you line up the marks on the pump before fitting you will not be far out. You may need to make a slight adjustment by slackening the bolts on the pump drive gear. Again this is fully explained in the workshop manual which can be downloaded from this site.

Gerald

Useful info thanks Gerald. Can one still get parts rather than replacement injectors I wonder?
I'm itching to check the lift pump first as I can see no reason why a previously correctly timed pump would move.

Rob

roromac wrote:I don't really want to remove the injector pump until everything else is tested. I have visions of timing woes...
Rob

Timing shouldn't be a trauma. Just do as Gerald says. To make doubly sure, you could remove the small round cover on the front of the timing cover, to expose the front of the fuel pump gear. Chalk up the timing lines on the pump gear and the idler gear, or put a blob of paint on the teeth where they mesh and take a photo. Don't turn the engine whilst the pump is off. When all is done, pop the pump back on in the same position.

Rob, Only a thought but you did set the valve clearances did'nt you ????
A way to check if one of the injectors is not functioning , is to fit the them and providing your engine does start, loosen the pipes on each one in turn should give an which injector is at fault. should be a spill timing mark on the flywheel to get the correct pump timing. Jim

Ben - good suggestion but i hope not to have to.

TKU YorkshireDextaMan. I did check tappets and all were and are fine. Number one injector is faulty; i shouldn't be able to blow through it to the leakoff port so apparently the needle is not mating with its seat. To add insult to injury, the pulse to that cylinder, if I loosen unions whilst cranking or running is weaker than to the other two.
However, I need to confirm that the lift pump is not full of dirt as flow to it is fine and from it on manual levering is fine. If that is good then the infector pump looks doomed
Rob

Its worth getting the injectors overhauled as its not a particularly expensive job (I used SOuthern County Tractors Spares) and if you have a pop tester, you could do it yourself.

Mark
Sadly I have no such tester. Do you know where I can get parts rather than the whole injector?

Agrline and most of the other suppliers do the nozzles but, you need a pop tester to set them up once fitted.

Southern county will refurb the injectors for £21 each (includes a new nozzle and setup)

http://www.southerntractorspares.co.uk/ ... a3552ab16a

The latter is the option I took but, I have since got access to a pop tester (and injection pump tester) so have also done some myself (including a set for a 6610 engine in a Snderson telepprter 2 recently)

UPDATE:
All 3 injectors replaced - Forge Sevices because I've met him and he had 3 awaiting. Uplift pump cleaned, no significant improvement. I now have 2 and a half cylinders firing and a lot of unburnt diesel in the exhaust - or so it smells. It seems to me counterintuitive that a worn injector pump would put too much diesel in. Anyway I took the injectors out and tried manipulating the pipes so I could crank the engine with the injecors in mid air to check the spray pattern. I checked the oulets one at a time, leaving the other two to squirt diesel into the air. I got NO spray through the injectors at all and a column from the unpiped outlets which reached about 2 to 2 1/2 feet.
As I can start the tractor, (with Bradex - don't shout), there must be a point where the injectors do work but I can't work out how.
This oints to a pretty worn injector pump to me - anyone disagree? This will most likely be a Peter Strong job.
Still can't work out how it gives too much diesel and no spray pattern. Am I missing something?

Rob

The very fact that the injectors are not atomising at cranking speed suggests that the injector pump is suspect, as it is unable to build up or sustain sufficient pressure (160 bar) to open the injector.

When you use Easy Start to start the engine, the engine will run a lot faster than cranking speed and with the injector pump rack on full throttle sufficient pressure can build up to open the injectors and keep the engine running at tickover. But as soon as you apply a load to the engine it slows down and stalls as the pump is unable to supply sufficeint fuel to the engine.

You have exhausted every other possibility so there is only one course of action, that is to take the injection pump to your local Diesel specialist. As I pointed out in an earlier post if it has run for 10,000 hours then it is hardly surpising that it has become worn!

Gerald

Gerald - that is the sorry conclusion I have reached. One more thing though - I assumed that spill timing couldn't move, it being mechanical and cog driven. On reading the instruction manual I not the three set screws appear to be the locking mechanism onto an adapter plate between pump and gear. This implies that there is some movement possible. Can't think why it would change but thst would explain unburnt fuel - otherwise, why would there be smoke if fuel starvation was the problem?

Rob

Even if the timing were out it would not prevent the injectors from atomising when you tested them.

For proper combustion, especially in a cold engine, the Diesel fuel has to be atomised and leave the injector in the form of a mist. I suspect that in your case the fuel is not being atomised atomised and unburnt fuel is carried over into the exhaust.

Gerald

Gerald
That makes sense. Logic has to follow for the diagnosis to work and I can see that lack of atomisation, just leakage would work... except will the injector actually work if the pressure is to low? If the firing pressure of 160 atmospheres is reached, won't atomisation take place on the burst anyway?
Rob

We though we'd check the timing, just for fun this evening. There are 2 spill marks on the flywheel, the first seemed to be marked 26 and the injector pump was nearer that than the other, which I assume is the 20 degree mark. However, the timing was out by about a tooth, retarded. We have adjusted it but haven't yet started it. I know, Gerald, it'll probably be the same but it's becoming a very useful learning exercise.
Rob

And you're right Ben, timing is no trauma

As I'm not removing the injector pump until next week I checked tonight to see if the idler gear and the pump drive gear matched their marks - they didn't. I couldn't even confirm a realistic mark on the pump drive gear. Equally, at 26deg before TDC the mark on the idler gear was nowhere to be seen. I wonder if this was a set up for the Dexta and pneumatic pump rather than NPSD and mechanically governed pump. If not then how could the tractor have run at all if my unrealistic marks were true marks but 120deg out?
Rob
By the way - after the minor timing adjustment, the engine responded better throttle? Coincidence? Maybe as it had done a few hours gang mowing on Tuesday.

roromac wrote:As I'm not removing the injector pump until next week I checked tonight to see if the idler gear and the pump drive gear matched their marks - they didn't. I couldn't even confirm a realistic mark on the pump drive gear. Equally, at 26deg before TDC the mark on the idler gear was nowhere to be seen. I wonder if this was a set up for the Dexta and pneumatic pump rather than NPSD and mechanically governed pump. If not then how could the tractor have run at all if my unrealistic marks were true marks but 120deg out?
Rob
By the way - after the minor timing adjustment, the engine responded better throttle? Coincidence? Maybe as it had done a few hours gang mowing on Tuesday.

The timing / assembly marks in the gear case all line up every 17 or 18 ( I forget which) revolutions...due to the ratios involved in the gears.

I've just realised what nonsense I've written: This is a Super Dexta with a 4588 pump. And I can't remember what the timing should be, 20 or 26 BTDC. Either way the marks on the timing gear look home made or coincidental and are nowhere near the idler gear marks when they're supposed to be.
Rob

As Commander points out, you may have to turn the crankshaft up to 18 revs to get the timing marks to line up. Given your engine does run, it's unlikely the timing is very far out.

I think I'll take Commander's word for it. It does solve the dilemma though.
Rob