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Remember the picture of the carburettor with a broken off slow running jet? that’s what I’ve been up to tonight. It’s too hot to do anything outside and the workshop is the coolest place, so I took a big breath and launched into it.
Access to it is easy enough, but it runs parallel to the main venturi pipe and so I couldn’t mount it in the pillar drill because the chuck is too bulky to get anywhere near. The solution was to use a flexible drive, very much like a scaled-down Tarpen arrangement, driven off the chuck on the pillar drill and used hand-held with some long drill bits. The much smaller chuck could just get in alongside the barrel and I took the jammed jet out in stages up to 3.5mm. You can actually see the drilled hole starting to break through to the threads in the one photo.
Next stage is to find the original size of thread and tap it out to the size, but I will have to go to my storage place to measure up my Steed to find this out.Attachments:
A nice thought. Judge for yourself from the photo’s whether you think you could make one for yourself, it’s really not difficult.
Anyway, onwards and upwards; a good day today.
You will see the different stages of making the slow-running jet from the photo’s, but basically you start with hexagonal brass bar 5/16″ across flats. Mark off the length of thread and shank and turn it down to the external thread size- in this case the thread is 3/16″ Whitworth, so you turn it down to 3/16″ or .185″.
I chose to put the thread on by hand with a die in this case because the thread is tiny and my eyesight is non too good on the small sizes to cut it with the lathe. The result was acceptable, so to finish the end off I turned a cone onto the tip of it and relieved the thread back about 1/16″ to copy the original.
Next job was to part it off the bar, mount it in the vice and hacksaw a screwdriver slot in the head then file it up to remove the burrs. An old spring from a Zenith carb that I had on the shelf completed the job. I hope it works!
The next item on the list was the slow-running adjuster screw which somebody had twisted off some time in the dim past. It is situated on a long arm and sits against the vertical barrel that houses the main jet. When in use it is a fine adjustment to alter the angle of the butterfly in the venturi and you can’t set an even tick-over without it.
First part was to mount it securely in a drill vice, then centre-punch it and drill it using the same method as before; using progressively larger drills I was able to open it out to 1/8″, then tap it to 3/16″ Whitworth again. I found a screw in the spares box, pinched another spring off the Zenith and the job’s done!
Re-assembly of the carb was quite straightforward using new fibre washers all round, but don’t forget to take a look at the cork seal in the base of the main jet holder. It is held in place by a gland nut that compresses it when the nut is tightened; if you forget it (or lose it like I nearly did) then the carb will drip constantly from the main jet adjusting screw, so it’s quite an important little bit of wood.
Both screws were set to 1 1/2 turns out as an initial setting; these will be adjusted once the engine is running.Attachments:
I’ve got a bit of catching up to do this time, I’m afraid. Besides other things getting in the way I have made steady progress on the project, so much so that it is finished apart from mounting the exhaust.
I will go through some of the more fiddly bits that got me scratching my head in the hope that anyone doing the same work can see how I tackled the job.
Starting from the front of the engine I decided to fit a new pipe to connect the air filter to the carburettor. This sounds easy, but I couldn’t find one with a suitable sharp bend in it and so I opted for a longer pipe with a more gradual curve; it may work better in keeping the airflow smoother as well, but only time will tell. It was secured at both ends with wire clips like the original was, not with jubilee clips which are definitely a much later idea.
Next to follow was the oil tank and it’s plumbing; this was something that I was dreading because the pipes are designed with an anti-vibration rubber joiner in them. Needless to say, the original rubber had become porous and brittle and wouldn’t have done the job for much longer if I’d left them alone, so back to the spares box to see what I could find suitable. A length of flexible diesel tubing came to the rescue and I thought that if it was suitable for diesel then it should be fine for engine oil. Do I just put it on and find some clips to secure it? I think you know the answer to that one- NO!
These pipes are similar to hydraulic pipes in that they have swaged ends and one of them has a swivel fitting to screw onto the tank outlet. Fortunately the rubber was so brittle that it could be picked out a little at a time to leave a clean surface inside, so I then mounted the swaging onto a round bar and hammered lightly until the swaging expanded very slightly, just enough to get the new pipe in. Once the rubber pipe was in I then tried the copper oil pipe in the centre for a trial fit and couldn’t get it out again it was such a tight fit! Counting this a success I then did all the other fittings the same way, apart from the swivel which had it’s own tail which I had to use a drift to drive in once the external swaging was in place.
I only took this course of action because the pipes do not carry any pressure, they only deliver oil to the oil pump and then return used oil to the tank; if they were to carry any pressure at all then a stronger pipe and fittings would be needed, and sourced from one of the many specialists that there are dotted around the country. Don’t be tempted to use this method on hydraulic pipework, no matter how low the pressure- leave it to the experts!
Cables were the next priority. If you can solder then you can make a cable, they are that easy; the most difficult part is getting the lengths of the outer and inner cables right, and also the fact that we are not furnished with three hands to hold everything in position whilst you solder the nipple back onto the cable. Patience and care are the keys to making a good cable; you can even use old cables if they are not too worn. That’s what I tend to do- I save old cables that have perhaps got a fray on the end but are otherwise quite sound and they provide the raw materials for making up shorter cables.
One aspect of the rebuild that really got me thinking was the arrangement of the throttle/governor linkage; how it came to me was obviously not right because somebody had added a tension spring to pull the linkage back to tick-over when the throttle was closed. How it had been assembled on the tractor looked correct but it worked the wrong way around- you could open the throttle and it would respond, but when you closed it the throttle stayed open due to a hairspring keeping the tension on the spindle the wrong way. No matter how I looked at it and turned things around I couldn’t seem to get it to work the way that I wanted until I had a Eureka moment and everything just dropped into place in a different order. I just hope it works when I fire it up!
Apart from a few more mundane run-of-the-mill bits and pieces that’s about it for the rebuild. Next time I will have re-fitted the exhaust and started it up (hopefully!).Attachments:
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