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Paul Lousick24/12/2019 20:46:46
1285 forum posts
512 photos

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.



JasonB24/12/2019 20:51:52
17066 forum posts
1839 photos
1 articles

The Fowler A7 has them at 38.2deg

John Olsen25/12/2019 04:23:21
1001 forum posts
86 photos
1 articles

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.


Nigel Graham 219/02/2020 00:33:59
461 forum posts

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.

Nigel Graham 219/02/2020 00:36:10
461 forum posts

Aaaarrrghh! Those blasted silly faces!

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

Nigel Bennett19/02/2020 14:50:12
313 forum posts
11 photos
Posted by Nigel Graham 2 on 19/02/2020 00:36:10:

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).

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