stephensons motion problem

stephensons motion problem

This topic has 7 replies, 3 voices, and was last updated 19 March 2020 at 11:16 by David Bothwell 1.

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18 March 2020 at 16:19 #33549
David Bothwell 1
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@davidbothwell1
Only run in reverse
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18 March 2020 at 16:19 #457996
David Bothwell 1
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@davidbothwell1
working on a recently purchased chassis, outside cylinders, inside Stephensons link motion, after a few adjustments I got the engine running, but only in reverse, motion transferred to the valves by outside rockers. Using the reverse lever to half speed produces no movement as does full forward. This morning I even altered the eccentrics to opposite position, no effect, Any advice or suggestion would be most appreciated. Chassis is Virginia 4-4-0 from e-bay and looked reasonably well put together
18 March 2020 at 18:03 #458024
Redsetter
Participant
@redsetter
Obviously we don't know what you have done already, but before adjusting the eccentrics the first thing to do is to centralise the valve on the port face by adjusting the valve spindle, so that the valve opens equally at each end of its stroke.
18 March 2020 at 19:42 #458040
David Bothwell 1
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@davidbothwell1
Thanks for that I have the equal opening and it runs like it should, but just in reverse!!!
18 March 2020 at 20:18 #458044
Jeff Dayman
Participant
@jeffdayman43397
What happens at the reverse links when you move the reverse lever all the way back and all the way forward? If these movements don't move the links a similar amount up/down for forward and reverse, maybe the reverse lever or lifting arms have slipped in rotation on their pivots.
18 March 2020 at 20:36 #458047
Redsetter
Participant
@redsetter
Okay, in principle with launch links the eccentrics should be set 90 degrees either side of the crank pin, then both advanced equally by an amount equal to lap plus lead. In this case you can ignore the lead component.

I would suggest that your reverse eccentric is set about right, but the forward one isn't.

Going back to the first sentence, the eccentrics should appear symmetrical either side of the crankpin but the angle between them will be less than 180 degrees.

I hope that makes sense.
19 March 2020 at 08:21 #458104
David Bothwell 1
Participant
@davidbothwell1
My thanks to both constructive and useful replies, I think the links are moving on an equal way/amount.. I will give the second reply a further investigation today.Sorry about the late response.
19 March 2020 at 11:16 #458148
David Bothwell 1
Participant
@davidbothwell1
Cracked the problem this morning, altered the eccentrics, but when applied air same thing going in reverse, just moved a wheel a quarter of a turn, Hey presto front running! Thanks everybody
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