Horizontal Twin

[warrenmaker]

Hey guys,

Flushed with my success with the Stuart 7A, I am beginning on my next project.

This will be entirely scratch built from bar stock, except for the fly wheel which I am turning from an old bar bell.
Please take a look at the plans I have drawn so far and see if you can find any glaring errors that might make it explode when I first plug the air in. 

The cylinder build will follow Jason's idea of milling the top flat and fitting the valve chest base with the steam passages already milled in.
If the plan looks familiar it's because it's basically a Muncaster simple horizontal; turned into a twin. Although being a twin required a lot of changes to the crank shaft.

Thanks again.

[Jasonb]

Looks about OK though I would probably have a slightly thicker piston. Plus set one crank at 90deg to the other.

You could save yourself quite a bit of work if you put the valve chests on the inside which would allow you to omit the outer two bearing pedestalls and have simple crank arms or disc cranks on the end of a straight crankshaft. Something along the lines of these couple of gems particularly the bottom one.

[warrenmaker]

Thanks Jason,

what lovely engines,, pity about the rust...

Why are the big end crank pins set at 90 deg to each other. I would have thought 180 deg would provide a smoother running engine. (I know I am going to regret asking that question)   

[warrenmaker]

Also; I made the pistons that narrow to maximize the stroke.

Actual dimensions are 38mm (1.5") bore and 44mm (1.75") stroke. Also; why in general do horizontal engines seem to have longer strokes than the vertical types?

[crueby]

Thanks Jason,

what lovely engines,, pity about the rust...

Why are the big end crank pins set at 90 deg to each other. I would have thought 180 deg would provide a smoother running engine. (I know I am going to regret asking that question)   

With double acting pistons, a 90 degree offset means that there are no dead spots and it will always self start from any location. Also, at 180 both pistpns would stop and start working at the same time so its more jerky a motion than at 90. 

[Jasonb]

Also; why in general do horizontal engines seem to have longer strokes than the vertical types?

The ones that run at slower speeds tend to have a longer stroke than bore but you do find them with near identical bore and stroke where the application requires a higher speed.