Hi,
I'm not familiar with the Gemini engine so I don't know if I am suggesting complete twaddle ...
I've been scratch building my own steam engine from handy materials. It's about 11.5mm bore x 10mm stroke, slide valve, non-reversing.
On compressed air (motor-car foot-pump) it would turn over and run sort of. I hooked it up to a steam generator - a length of 3mm (1/8th) copper tube coiled in flash-steamer fashion over the kitchen gas stove. Nothing, nothing, nothing!
Timing, that's it.
If you stripped the engine, it is almost certain you a/ put the eccentric back on the crankshaft at a slightly different (angular) position from its original, and b/ altered the eccentric-to-valve distance.
Try this:-
Set the reversing lever full over for the direction you want, and lock/clamp/wedge it there.
(At any in-between setting, the reversing gear will reduce the valve travel so as to consume less steam. At mid-gear, the valve will not open to admit any steam at all. By and large, this is not required for a model boat.
With the steam chest in place but its cover off, rotate the engine, in the direction you want it to go, to top-dead-centre (TDC). The slide valve should have started down to the point where it is just beginning to uncover the port which admits steam to the top of the piston.
1] Adjust the eccentric-to-valve distance - usually the valve rod is threaded, with a locknut onto a clevis for the eccentric-strap - to split the difference between the port openings at TDC and BDC. It will take a few tries to get it somewhere handy, because the clevis can only be moved by half-turn increments.
2] Slacken the eccentric (grub-screw?) that is doing the pushing for this direction, and rotate it around the crankshaft till you can just see a crack of the port above the top-edge of the valve - a boars hair, as they say. Nip the eccentric in place, gently!
A useful guide is that the valve should be about 70 decgrees in advance of the crack: rotate the crank until the valve is as high as it will go and the crank should eyeball to be a bit less than 90 degree behind TDC in the direction of rotation.
3] Rotate the crankshaft to bottom-dead-centre (BDC) and view the bottom port. It will likely be more open than the TDC - in other words, it started opening earlier than it should have.
Back to [1] and try again (and again), until both top- and bottom ports are just uncovering/opening pretty much the same small amount at TDC and BDC.
For reverse, you will simply put the reversing lever full over the other way and work on the angular position of the other eccentric. Do not mess with the clevis.
Geoff
