Stuart triple timing

[Steamingandy]

Timeing a Stuart triple is often considered a black art, this is hopefully shows one of the the problems that I think gets overlooked,the drawings have a note on them stating “if the ports vary from the drawings adjust the length of the valve to suit”.
This engine shows exactly why this is important
To the drawings the port positions require the Valve to be 0.625” long
This engine has both inlet ports larger, lower 0.022” over size and the upper 0.060” over size total of 0.082”.
So the valve for this cylinder is 0.707” instead of 0.625”
The exhaust port is to size so valve is machined to drawings.
Hopefully this clear enough to understand with the pictures.

 

[Steamingandy]

Setting the eccentrics on the crankshaft

 

[oldengineguy]

Steamingandy: I built a Stuart triple last year. My drawings showed a 30 degree offset for HP cyl and 15 degree for IP and LP . Couldn't get the d--- thing to run forward and reverse on comp air with this set up. Made IP with 30 degree offset and eventually made separate eccentrics for LP as there is room to put them on shaft with bosses facing out. I don't know what the eventual offset ended up at on the LP cyl. I know I'll never run this on steam so don't care what Stuart say's it's supposed to be. All I know is it runs smoothly at as low as 40 RPM forward or reverse on 15 psi. Have run as fast as 1600 RPM @ 60 psi. I'm happy with the result ,engine finished on the shelf with others gathering dust . On with next and the next. P.S. The valve ports in mine were way out of spec too.
Good luck with it . It's a beauty to watch running.
Colin

 

[Steamingandy]

Steamingandy: I built a Stuart triple last year. My drawings showed a 30 degree offset for HP cyl and 15 degree for IP and LP . Couldn't get the d--- thing to run forward and reverse on comp air with this set up. Made IP with 30 degree offset and eventually made separate eccentrics for LP as there is room to put them on shaft with bosses facing out. I don't know what the eventual offset ended up at on the LP cyl. I know I'll never run this on steam so don't care what Stuart say's it's supposed to be. All I know is it runs smoothly at as low as 40 RPM forward or reverse on 15 psi. Have run as fast as 1600 RPM @ 60 psi. I'm happy with the result ,engine finished on the shelf with others gathering dust . On with next and the next. P.S. The valve ports in mine were way out of spec too.
Good luck with it . It's a beauty to watch running.
Colin

Adding very light springs to hold the valve against the ports makes running on air a lot better all cylinders work properly

 

[Mechanicboy]

Steamingandy,...

No need to put spring pressure on the valves as it is the pressure whether it is steam or air pressure that ensures that the valve gets in place on the cylinder. I have the same Stuart triple expansion steam engine as yours and have run on air with no problem. Cylinder oil also allows for a better seal while lubricating between the valve and the cylinder. With springs, wear can be amplified in the valve rod and the holes in the steamchest and gland leading to the holes become oval.

Adding very light springs to hold the valve against the ports makes running on air a lot better all cylinders work properly View attachment 135533

 

[Steamingandy]

Steamingandy,...

No need to put spring pressure on the valves as it is the pressure whether it is steam or air pressure that ensures that the valve gets in place on the cylinder. I have the same Stuart triple expansion steam engine as yours and have run on air with no problem. Cylinder oil also allows for a better seal while lubricating between the valve and the cylinder. With springs, wear can be amplified in the valve rod and the holes in the steamchest and gland leading to the holes become oval.

The two I have built will run without but they definitely run better with the springs
If it was running on steam there would not be any benefits