Upshur's opposed twin engine

[Steamchick]

Happy Thanksgiving. Enjoy family time.
😊

 

[Brian Rupnow]

I just received this email from R Klopp, who successfully built and ran six (not eight) of these Upshur opposed engines.
Hi Brian

I based my Upshur valve timing on the Wyvern design and came up with these numbers:

Wyvern timing (based on crank angle) is reportedly as follows:
Inlet: 230º duration, open 5º BTDC, close 225º ATDC, lobe centered at 110º
Exhaust: 255º duration, open 235º BTDC, close 20º ATDC, lobe centered at 107.5º BTDC
Offset between the lobes based on cam angle is therefore 108.75 º
Both valves are equally open 7.5º ATDC.

I machined the Upshur cams to these numbers, and I think the reality came pretty close to the numbers. I suppose the main thing for you is to set the angle between cam lobe peaks to 108.75° or thereabouts. You can then shift the cam-to-crank gear engagement tooth by tooth until you get the intake opening as close to 5° before TDC as you can.

This post has a decent explanation: https://www.model-engineer.co.uk/forums/topic/centaur-valve-timing/page/2/

Some old info here: https://www.homemodelenginemachinist.com/threads/upshur-twin-valve-timing.32825/
and here: https://www.modelenginemaker.com/index.php/topic,3793.msg68882.html#msg68882

Please consider copying this info to the main thread so the rest of the community can benefit.

Good luck!

 

[rklopp]

Brian is way too generous. I didn't build 8 . I wish my teachers gave me that much extra credit back in the day.