DCB Posted March 6, 2021 Share Posted March 6, 2021 Its been bothering me. I'm used to single acting non reversible internal combustion engines with their cam timing, and indeed VVC variable valve timing, not steam locos with reversible double acting cylinders. What I want to know is 1) Were the eccentrics for the valve gear cast and machined as one with the axles or could they be adjusted to adjust the lead etc of the valves. 2) Did 1/4" lead in forward gear become 1/4" negative in reverse with Walchaerts gear, and 3 did the same apply to Stephenson motion or did the positive in mid gear become negative when in reverse. Sorry for such anoraky questions but... Link to comment Share on other sites More sharing options...
LMS2968 Posted March 6, 2021 Share Posted March 6, 2021 Not really my area of expertise, such as it is, but 1) the eccentrics were made in two halves then bolted together around the axle, a keyway ensuring they didn't rotate on the axle. 'Adjustment' would mean a new eccentric with the keyway in a slightly different position. 2) Walschaert's gear's lead was provided from the crosshead via the combination lever and would be positive at each end of the stroke. 3) Stephenson's gear used separate equal links coming off equal eccentrics for fore and reverse gear, so the lead would be provided by the links independently and the same both in fore and back gear. If there's anything wrong with this, I'm sure others will soon be along with the correct answers. Link to comment Share on other sites More sharing options...
PenrithBeacon Posted March 6, 2021 Share Posted March 6, 2021 21 minutes ago, DavidCBroad said: Its been bothering me. I'm used to single acting non reversible internal combustion engines with their cam timing, and indeed VVC variable valve timing, not steam locos with reversible double acting cylinders. What I want to know is 1) Were the eccentrics for the valve gear cast and machined as one with the axles or could they be adjusted to adjust the lead etc of the valves. 2) Did 1/4" lead in forward gear become 1/4" negative in reverse with Walchaerts gear, and 3 did the same apply to Stephenson motion or did the positive in mid gear become negative when in reverse. Sorry for such anoraky questions but... Too which valve gear design are you referring? Link to comment Share on other sites More sharing options...
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