Douglas SV54

[aquila787]

Hello again

I’ve acquired a Trusty tractor with a Douglas SV54 engine. Anyone know where I can buy a new head gasket for it.

I’ve no compression in the cylinder and I think it’s leaking through the gasket. Could be something else too but I’d need the gasket if available anyway.

Kind regards
John

[trusty220]

The Douglas SV54 isn’t one that I’ve worked on but most of the other engines from that era seem to have a solid aluminium gasket which can be re-used. If it’s gone too far at least you can use it as a template to cut a new one out of aluminium plate.

If you don’t have any compression- and the tractor’s been standing for some time- the most likely culprit is the exhaust valve being stuck open. Just about every Trusty I’ve rescued has had a stuck exhaust valve! Moisture will get in via the exhaust and cause the valve stem to rust, then it sticks in the guide when it’s turned over next time.

Let us know how you get on.

[aquila787]

Well I’ve taken the head off and had a look. Valves are working as they should. Timing seems spot on. The gasket is copper and is ok-ish few little spots of black carbon. Valves look OK. I suppose they might benefit from grinding. Don’t think any of that would account for zero compression though (correct me if I’m wrong). The only other thing I’m thinking is leaking past the piston rings. There’s no marks on the cylinder wall. It might have been “worked” on recently as the honing marks are clearly visible.

I suppose the only way I’m going to find out is to take the cylinder off.

John

[john-e-w]

Hi John – been round this loop with my Monroe tiller. Ended up replacing the rings – but don’t forget to gap them halfway down the barrel and make sure the gaps are not lined up when you replace the rings.

However, as its a copper gasket, you could try annealing it and putting it back on the head. Heat the gasket until it is cherry red, then just leave it to cool – do not quench in oil or water. However, if after trying the above you still have absolutely no compression and the valves are working OK, then unfortunately the problem is likely to be rings.

Best of luck

John E-W

[trusty220]

If you’re sure that the valves are sealing make sure that the head is flat by getting a sheet of emery cloth, lay it out on something that you know is flat (like a piece of glass) and rub the underside of the head on it using a circular motion. It’s surprising how much some of these heads can distort over time and the rubbing marks will give you an idea how much- or how little- it’s out of true.

If it’s not the head, head gasket or valves then it has got to be the piston rings. Cylinder bores tend to wear more at the top than the bottom and if your engine has been standing it’s a good probability that the old oil will have glued the piston rings in. Turning the engine over will compress the rings on the piston as it moves down the tapered bore, then they don’t spring out again as the piston comes back up. Have you tried some engine oil down the sides of the piston to see if it raises the compression?

[aquila787]

Might try that oil trick, tomorrow though. Thanks

[aquila787]

There’s a sprocket on the side of this trusty tractor. Don’t know what it could have been used for. Any ideas?

John

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[trusty-mad]

That would have been to run a belt pully as in this photo.

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