Stuart twin compound

This topic has 4 replies, 2 voices, and was last updated 20 October 2026 at 16:45 by JasonB.

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20 October 2026 at 16:01 #870394
teamricky
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@teamricky
Hi all,

I have just built a Stuart twin compound and in the process of running in 😁

It was built up from pre war parts , base , rods ect but with a new cylinder block as that was missing!

Question for anyone with experience of the engine: how low on pressures should I expect when running one cylinder at a time, I ask because I’m setting up the cylinders ect one at a time and looking for a bench mark in terms of quality of build and set up 😀

Thanks in advance

Ricky
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20 October 2026 at 16:08 #870395
JasonB
Moderator
@jasonb
Have you built a Twin = 2 cylinders of the same diameter or have you built a Compound = cylinders of different diameters.

Next how are you running the single cylinder? Is it having to move the other piston and do the pistons have rings fitted. Both these factors will affect the drag and that in turn affects the pressure needed to overcome that drag.

If you don’t have the other piston rod connected 5psi should do it but lets say 10psi for a new one that is a bit tight and needs the rings bedding in.
20 October 2026 at 16:19 #870397
teamricky
Participant
@teamricky
Hi Jason,

it’s the compound running on a compressor, Currently runs on 10 psi as you say dragging the Lp cylinder currently, it much happier at 20 psi ! I guess a good few hours probably needed to then fine tune the valves? The rings are Viton with a little light oil in the cylinders probably now mixed with a bit of steam oil …

Thanks for your reply

Ricky
20 October 2026 at 16:21 #870398
teamricky
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@teamricky
20 October 2026 at 16:45 #870400
JasonB
Moderator
@jasonb
A compound will never really run well on air, some people find it better to have a “simpling” valve which effectively runs both cylinders at boiler/compressor pressure. If you can take the linking pipe off and put air into both inlets that may improve things.

If you are only going to be running on air then stay away from the steam oil, it is a bit too thick and sticky (even the light grade) until it gets heated by the steam which won’t happen on air.
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Stuart twin compound

Stuart twin compound

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