Trusty Steed engine rebuild

[charlie]

Al you need to do now Geoff is put all this into an article (serialised) for The Cultivator.

[vhgmcbuddy]

Steve Woollas warned me about letting you anywhere near my Trusty, Geoff. Something about you filling the petrol tank on one of his Trusty’s with “The Good Stuff”, after which the engine refused to run at all!!!
Seriously though, I appreciate the offer of help, but I am sure that I just need to fettle the carb a touch. The magneto is fine, as I had it professionally rebuilt. My only other concern is the amount of compression. With spark plug out, engine turns over without too much effort. Plug in is a different story. I can drag the entire tractor (with plough attached) towards me when pulling the starting strap. I can just about manage 2 complete revolutions of the engine (i.e. one complete 4 stroke cycle). Is this normal? The piston rings are new, being gapped at 0.030″ for the compression rings and 0.008″ for the oil scraper ring. The engine manual gives a compression ratio figure of 4.8, so I think I will borrow a compression tester and see what’s what.

[trusty220]

That doesn’t sound normal at all, I’m afraid.

My best guess is to look at the magneto timing because it sounds a little too advanced. It can produce the effect that you describe without being too far out of adjustment.

The best way to double check it is to remove the cover plate on the top of the cowling and unscrew the bolt (which is really a plug) underneath. This will allow you to insert a rod straight down onto the piston crown so that you can find TDC without dismantling anything. It is then easy to turn the engine backwards so the piston descends 3/8″.

Another mistake that I’ve seen with these Big Four engines is that the direction the magneto turns is different, depending on the model. The one you should have is the 639cc version as opposed to the 598cc version that is found on the 2-wheeled Trusty.

As the 639 takes the magneto drive off the inlet camshaft the points assembly rotates in a clockwise direction, but the 598 takes the drive off the end of the crankshaft and the mag turns the opposite way. If you are following the wrong manual you may have got the timing wrong and not be aware of it.

I’m assuming that you have retarded the magneto before starting and that the adjustment doesn’t slip back to fully advanced on it’s own?

By the way- the Trusty that Steve “the Gnome” was talking about belonged to me, and it was his “drop of the good stuff” that b*****ed up my engine. It ran fine until he put some Lincolnshire cocktail in, and it ran fine again once I’d taken it all out again and put some good old Shell Unleaded in. Draw your own conclusions, but he’s not allowed anywhere near the filler cap any more!

I hope that helps, Sean. The offer’s still open if you want it.

[trusty220]

The final part of this saga took place yesterday when we took the Trusty back to Wales. Lovely weather (as you can see from the pictures) but it didn’t go entirely according to plan.

We got there nice and early so that the owner, Pete, could have a good look at it before he went off to do his voluntary work at a local museum. Once at the farm we unloaded it onto a piece of level ground so that I could start it up. As you can see from the pictures there isn’t much level ground in the neighbourhood, but there was a bit at the back of the trailer and so I prepared to start it up where it was unloaded.

Wind the strap onto the pulley, set the throttle to 1/4 open, turn the petrol on and flood it on the carburretor, set the ignition to “Retard”- the advance/retard cable came loose at the magneto end! It was either the nipple had come off the cable or the cable had come out of it’s collet inside the mag, so I had to do a quick strip down to find out.

Luckily it was the latter- I think the cam ring had jammed in it’s housing, then when I moved the lever the cable pushed the collet out of it’s location and came free. A quick re-assembly, tightening the collet at the same time so that it couldn’t happen again and fingers crossed- it started! Pete couldn’t climb up onto the footplate because of his arthritis, but his son Barry had a go and went for a spin up and down the farmyard. It was going great until yours truly had a go back up the farm drive; I put it into third gear and gave it full throttle, then halfway to the top the engine just died. Jumping off I found that the nipple had come unsoldered from the end of the petrol pipe, so it was back to the farm to see what we could do.

Pete’s neighbour, Dave Packer, came to the rescue with a calf de-budding tool. It was really a large soldering iron that you could clip onto a tractor’s battery so that you could de-bud (de-horn) calves in the field, so Barry brought the Nuffield round and we set to work trying to get enough heat into the joint to melt the solder. As you can see from the pictures it was a team effort to repair it but eventually proved successful. Quite an eventful morning and I can’t thank Barry and Pete enough for mucking in to help.

It was quite ironic that the parts that let me down were parts that I hadn’t worked on- the magneto was an outside repair and came back with the cable fitted and the petrol pipe seemed fine when I polished it up; it just goes to show that you can’t take anything for granted. It reminds me of a blackboard in one of my customers’ workshops- in big letters across the top is chalked, “ASSUME NOTHING!”.

How right he is!

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