I would like to make a finely adjustable gas needle valve and would value some pointers as to the design. Its for a small gas engine, Stuart 800.
The mixer shown seems to work OK on another engine, even if its lacking in its visual refinement.
I need a fine thread, BA, BSB or ME no problem.
Now should the threaded brass part be bottoming out when screwed fully in, or more likely the needle itself??
In this example the needle is 1.8mm dia, so drill a hole that diameter with a standard drill bit ?, or should the tip of the needle seat into a matching tapered hole?
Should the needle have a longer taper? Ideal material for this?
Is this a good basic design, or are there published designs/ sketches available?
Any help gratefully received.

Quote from: jwloach on April 19, 2025, 02:07:36 PM

My grandfather ran the engine with compressed air, but he had to remove all the piston rings to make it cycle easily enough. Perhaps he didn't let it 'run-in' long enough. I'll start the reassembly after freshening up the paint on the base and cyclinder housings.

The problem with running a triple on compressed air, is air does not behave the same as steam.   The available expansion of compressed air in the 120 psi range is quite limited compared to that of steam.  The result is the IP and LP cylinders will over expand the be operating under a vacuum, in opposition to the HP ( high pressure) cylinder.    This results in lumpy running   if you open the drain cocks on the IP and LP it will help a lot,   Additionally, you could run some compressed air to the IP and LP.

Dave

Does the engine have a simpling valve? This is a valve that allows high pressure steam to be fed into the valve chest of a lower pressure cylinder. It is used to start the engine when the high pressure piston is close to top or bottom dead centre. Without it the engine may not start. One can be made and fitted with ease.

AVTUR

Advice with crank please

I have not made this type of crank before and was wondering the best & simplest approach - see diagram. At the moment I'm thinking rectangular stock with 2 holes 0.750" apart, stepped roughly to the correct heights for each boss, and then the rotary table to mill the 2 bosses? I think the intersecting piece between the bosses is visually nice and can be filed afterwards?

How do I hold the work for milling on the rotary table; it looks too small to clamp it directly to the table and will a 4-jaw chuck work?

Thanks as always.....

Hello to everyone, I was a auto technician for 16 years. Changed gears and became a machinist for the last 14 years or so. Currently working as a manual Machinist on electric light rail passenger trains. Was lead to this forum from the Morrison and Marvin Engine works vise projects. I do love me some vises and scale models!

Cheers!
Rich

....Just wheelin along!