chrisben Posted July 6, 2012 Share Posted July 6, 2012 Hi I am busy building this DJH kit SAR GMAM.Please see attached photo ,not sure about the wheel link. Thank you Link to post Share on other sites More sharing options...
nzgresleyfan Posted July 6, 2012 Share Posted July 6, 2012 Hi there, and welcome to RMweb. The answer to your question is no, it needs to rotate. Everything will tie itself up in knots otherwise, very spectacular to watch at speed... The valve gear on your model is the Walschaerts type; rather than try and describe how it operates here I've provided a link for you to have a look at. There is an animated diagram which shows how the system works and is very useful. I won't try and describe which bit is attached to what on a model in order to get the desired action; my experience of this type of gear is limited to replacing parts on RTR locos and I'd probably end up telling you to solder the return crank to the wrong bit... I'd recommend changing the title of the thread to more accurately define your question, for example: "Return crank motion on DJH valve gear". I guarantee you'll get an answer very quickly; I do recall seeing a similar discussion recently on here but can't recall whereabouts, or what it was called. Good luck with your project! Regards, Rob. http://en.wikipedia.org/wiki/Walschaerts_valve_gear Link to post Share on other sites More sharing options...
Arthur Posted July 6, 2012 Share Posted July 6, 2012 It does need to be fixed, it's rotation is fixed in relationship to the wheel crankpin. With the crankpin bottom dead centre, the return crank should be upright with a little lean forwards or backwards, 5 degrees seems to ring a bell, (this depends on the way the valve gear is set up on the prototype and will be one OR the other). It's this lean which gives it the necessary eccentric motion relative to the wheel. I use Romfords/Markits and with these I use a full size, spare, crankpin washer (not a thin spacing washer) on the crankpin, outside the connecting rod, I place the eccentric crank on it, cut and file the excess off the crankpin, and then quickly, but securely, solder the eccentric to the pin and washer. The washer gives a bigger area to solder to and acts as a barrier to prevent solder getting down to the connecting rod, which does, of course, need to be free. This being one of the trickier bits of outside valve gear construction, soldering one bit firmly on without soldering the whole lot solid. A spot of oil on those bits first may help.The crankpin itself needs to be VERY firmly screwed into the wheel otherwise any stiffness in the motion will unscrew it. Others who use Gibsons (and even Markits) etc. may be along to describe their methods. Link to post Share on other sites More sharing options...
Ohmisterporter Posted July 6, 2012 Share Posted July 6, 2012 Welcome to the forum , please keep us posted as to your progress. Hope you find the above advice useful. Link to post Share on other sites More sharing options...
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