Super Dexta cold start primer

This forum is about the Fordson Dexta, Super Dexta and Petrol Dexta.
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ianpdexta
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Super Dexta cold start primer

Post by ianpdexta »

I finally got my Super Dexta started yesterday, now the injection pump has been refurbished. It took a lot of cranking and it filled the shed with white vapour. Eventually firing on one cyIinder then 2 then 3. I tried to use the heater and fuel primer but it didn't seem to help much, on taking the hose to the air filter off I could see the coil glowing brightly and fuel was being issued when I pumped the primer but there was no fire, not even any vapour. So I think the jet from the primer brass tap was squirting but missing the hot coil.

Maybe I can rotate the tap to redirect the jet but the question remains:

Should it be a jet or a spray? :?:

Once it was running and I drove it out of the shed for the first time in several years it ran quite nicely with no visible smoke. :D

Regards

Ian
Last edited by ianpdexta on Sun Jan 15, 2017 8:32 pm, edited 1 time in total.

sky blue
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Re: Super Dexta cold start primer

Post by sky blue »

it should be a fine mist like , so when it hits the hot coil it will ignite, the flame is then drawn
in an all being good the engine bursts into life, sometimes life isnt that simple though as we all know
but it needs to be a fine spray :D good luck

ianpdexta
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Re: Super Dexta cold start primer

Post by ianpdexta »

Thanks Sky Blue, I will take it off at the weekend and see what is going on.

Regards

Ian

ianpdexta
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Re: Super Dexta cold start primer

Post by ianpdexta »

I had look at the spray from the primer tap, it was not a fine mist but was a coarse spray a bit like from a pump action household cleaner like 'Flash', (guess who cleans the sink :| ) the more important thing, on closer inspection the way the inlet manifold is made, the spray doesn't point at the hot coil at all, it is getting on for an inch off set.

In desperation I pointed the spray directly down the inlet pipe as per picture, this works a treat, the diesel burns instantly and the engine started very quickly.

Image

Obviously I can't leave it like this, so I don't know what I can do to make the spray finer. May be if it does make a fine mist this will be drawn over the hot coil when you start cranking.

That leads me to another thought, it seems like you need 3 hands when using the cold start, heater button, primer pump and starter lever.

Any thoughts or help would be much appreciated, I don't suppose anyone knows of any primer taps available as New Old Stock

Regards

Ian

charlie63
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Re: Super Dexta cold start primer

Post by charlie63 »

Sorry to butt in to this post guys.
My 58 Dexta is fitted with the manifold heater type with the primer pump on the fuel tap. Im sure the ball inside the heater is stuck as when you push the primer when the heater is heating it just builds up pressure and isnt letting the diesel through the heater. Strip down required when I get home.
Question is should this type of heater be fitted with a fuel tap inline so as you can switch off the fuel once its started.

sky blue
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Re: Super Dexta cold start primer

Post by sky blue »

the only way to get an orignal tap would be off a scraped dexta or scrap yard or our beloved
fleabay, i dont know if the new type have the same spray as the older type although
all the suppliers will say they are excally the same , :roll:

PghBill
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Re: Super Dexta cold start primer

Post by PghBill »

" That leads me to another thought, it seems like you need 3 hands when using the cold start, heater button, primer pump and starter lever.
Ian,
My Super came with no atomizer or tap and a burned out heater. I solved the "3 hand problem" by installing a manifold heater from a Fergy operated by a 12 volt 30 second time delay relay. Push the heater button and your heater stays on for 30 seconds. Easy to wire.This frees up your hands to operate the primer and starter. This heater is thermally operated. Opens to let fuel pass thru when it gets hot and shuts off fuel when it cools. Fits right in. Cost about $20.00 in the U.S. Relay cost me about $10.00.
Bill

Heater Plug, Fuel. For tractors with Standard Motors 23c diesel engine.
OEM # 1021910M91.Application: Ferguson TO35, FE35.

ianpdexta
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Re: Super Dexta cold start primer

Post by ianpdexta »

I have ordered a new tap from Agriline but it will be a copy and I don't know if it spray any better than the present one, in fact I have a feeling that the existing one had come from the same source. I will test it outside the manifold first where I can see the spray.

Charlie63 - I ended up taking my old tap to pieces, there is no ball in side the it, so if nothing comes through maybe the jet is just blocked. But beware of prodding the hole out, there is a top hat behind it and it has a side facing hole which is smaller in my case. In fact someone has probable enlarged the outlet hole and that might be what has spoiled the spray.

I think the purpose of the tap is to prevent fuel from bleeding slowly into the manifold overnight, I have a feeling that only UK models had it fitted?

I might consider the later "Thermostart" but two things,
1 keeping it original,
2 the down side of the thermostart is that you don't necessarily know when it ignites, if you crank too soon there will be no flame, no benefit, if you crank too late I imagine the flame would soon go out due to lack of air? I remember using one a BM Volvo combine, it would not start without heat, I used to pull the air inlet hose off during startup and then could see the flame straight away.

At least with the manual pump you can wait as long as it takes for the heater to glow brightly, then pump fuel which should ignite instantly then start cranking.

I'll let you all know how I get on with the new tap.

Regards

Ian

charlie63
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Re: Super Dexta cold start primer

Post by charlie63 »

Ian,

Its the thermostart type manifold heater that is fitted to my Dexta but now reading the several replies on this topic I realise I dont need a tap to turn off the fuel as there should be no leakage in to the manifold with this type manifold heater as the spring inside the heater should keep the ball seated until the pressure from the primer pump is activated whilst heating.
I didnt realise the other type actually uses the tap to spray fuel into the manifold and then onto the heater.
It will be interesting to see how you get on with your new tap.

shawnee
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Re: Super Dexta cold start primer

Post by shawnee »

Manifold heater and atomizer is a bullet proof system for starting the dexta, keep in mine parts 50 to 60 years old do not last forever and need replacing :clap:
Last edited by shawnee on Sun Dec 18, 2016 5:19 am, edited 1 time in total.

Bensdexta
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Re: Super Dexta cold start primer

Post by Bensdexta »

charlie63 wrote:My 58 Dexta is fitted with the manifold heater type with the primer pump on the fuel tap. Im sure the ball inside the heater is stuck as when you push the primer when the heater is heating it just builds up pressure and isnt letting the diesel through the heater. Strip down required when I get home.
Question is should this type of heater be fitted with a fuel tap inline so as you can switch off the fuel once its started.
I believe the inline tap was a later 'fix' to, as you say, stop fuel dribbling out of a leaky primer.

The original primers (combined with a shut-off tap) under the left side of the fuel tank are not the most reliable bits of kit. Furthermore they are virtually impossible to service as they can't be easily disassembled.

I've fitted a modified primer to my shut-off tap, with a Stihl chain-saw primer bulb. This has a built-in valve to prevent dribbling. Still working great after 5 yrs so far. When the time comes, it will be easy to replace the Stihl bulb.
Bensdexta - 1961 working for a living!

ianpdexta
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Re: Super Dexta cold start primer

Post by ianpdexta »

I have at last got a cold start primer tap working well today, but before anyone says where did you get it? I have to point out that has not been easy, I have had to make and tested several versions before reaching this happy position.
This is the reproduction tap which happened to come from Agriline, but the general view is that other suppliers are probably offering the same thing? I mentioned earlier in this thread, this tap makes a jet which misses the hot coil, so no flame :(
Image


I tried to make an atomising spray head the same as used on plastic plant spray bottles, but didn't get the same result. They seem to work on the principle that a flat round surface is positioned very close just behind the small diameter jet hole, I assume so the liquid has to move fast and then suddenly change direction, my model engineering skills didn't seem up to making that work.

Next I modified the outlet of the tap with some 1/8" dia copper tubing and silver soldering. the tube bent round at 90 degrees with the intention at least of pointing the fuel directly at the coil. I made this too big and it fowled on the coil while screwing it in which nearly damaged the coil.

Next I researched and looked at other 'low pressure, liquid only spray jets', and found that some have narrow slot across the jet. I think the principle is that the otherwise round jet column of fluid coming from the jet touches the sides of the slot and is broken up in doing so. The slot was made by a junior hack saw blade which had been ground to a knife edge, then the slot was nipped up a bit in the vice, the result isn't very pretty with the repeated silver soldering not helping.
Image

The jet hole behind can just be seen here,
Image

Here is a view looking into the maniflold which I had removed it to make sure I had jet pointing straight on to the coil. The tap didn't tighten up in the right place so it remains about 1/2 a turn slack however the copper pipe from the fuel tank is tight and it alone prevents the tap from rotating.
Image

This one produced a reasonable spray, not a fine mist but it does point straight at the coil and more importantly it flames as soon as fuel is pumped, and the engine starts very nicely. I realise that this solution is not for everyone, I only wish I could point towards a simpler method, but it works for me and now at last I can move on to other restoration jobs.

I have found that the '40 seconds' advised period of preheating before pumping fuel, is rather long, the coil seems to be quite hot enough in 20 seconds, and doesn't really get much hotter if you wait longer.

One thing that I am aware of is that the compression is quite low on two cylinders, this is very noticeable when turning the engine over slowly with the starting handle. It is probably suffering from past ether abuse, in time I expect to rebuild the engine with new liners pistons and rings. when this is done hopefully it will start anyway unless it is very cold, in the mean time I still have a useful tractor.

Regards

Ian



I

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