Eccentrics

The valve eccentrics on my Ruston Proctor SD traction engine are set at 32 degrees (as shown on the supplied drawings) and the engine is running OK but I would be interested in knowing what angle other engines are using.

Paul

The Fowler A7 has them at 38.2deg

The ideal lead on the eccentrics will depend on the lap of the associated valve. If you are sufficiently curious, you could measure all the relevant parts and do a diagram or better yet, use the Dockstater software to see what the events are like.

John

The angle of advance is set by the designed lead (usually a tiny bit > 0 " as well as lap, so varies from engine to engine, but a bit over 30º seems quite typical for Stephenson's Link-Motion, full admission port openings and fairly late full-gear cut-off.

In fact your drawing gives what appears to be the lap (7/32 " and lead (that ' +1/64'. Which is quite possible as a traction-engine's engine itself, is designed to run fairly fast.

If I recall aright, the angle of advance on LBSC's Maid of Kent with Ken Harris' version of its Stephenson's Gear is around 35º. A loco is designed to be driven at speed on a very early cut-off, and the effect of that link motion is to increase the lead with notching-up, especially beyond what appears typical for a traction-engine.

The usual plots for eccentric / crank geometry are the Zeuner or the Reauleaux Diagrams, or simplified versions, both quite easy to draw. They simply relate valve-travel to crank and eccentric positions at dead-centre, but not the port openings themselves, nor the full effects of all the bits of steel in between.

Aaaarrrghh! Those blasted silly faces!

I thought I'd given the spaces necessary to prevent them, and I cannot edit them out!

Perhaps you should use millimetres instead... it's the inch symbols coupled with the brackets that causes the problem! (I'll get me coat).

Thanks Nigel!

Yes- I know the cause but I'd forgotten!

It would be beyond my computing knowledge but I do wonder if forum moderators are able to turn them off.

In that case too the drawing given is in inches so replying in inches was appropriate.