Clarkson [Jackson designed] Schools loco

[John RutzenParticipant @johnrutzen76569]

Clarkson Schools class loco re-designed for piston valves.

I am building one of these in 31/2 gauge.  I have made the cylinders and piston valves.  The original was slide valve.  It was designed by Jackson in 1934.  I am struggling with adapting the valve gear.  I’ve looked at the simulators available but I can’t see how to use them.  Does anyone please know which is the easiest to use?  I made the piston valves with the same port widths and lap as the slide valves thinking it would just be a case of swopping the connections on the link between the valve rod and the expansion link but i think there is more to it than that now I have read Don Ashton’s website about Walschearts gear.  Has anyone adapted a slide valve design to piston valve?

[John RutzenParticipant @johnrutzen76569]

Ok, i will reply to this myself since the problem has been sorted.  I didn’t get any replies so I went onto Don Ashton’s pages and with a few tries and lots of reading I used his spreadsheet to design the valve gear.  I discovered that very small changes make very big differences so one lesson is that the parts have to be very accurately made which I didn’t appreciate.  Also it’s possible to try subtle alterations to get it to fit into the design.  After this I used the Wallace simulator which Don references.  Again it didn’t turn out right to begin with but I found that by adjusting the valve setting by just 0.020 it all came out right and the valve events were really good.  So to anyone else who fancies changing a slide valve engine to piston valve i can thoroughly recommend Don Ashton’s website to design the valve gear.  I also think it would be no bad thing to put the dimensions into it of any valve gear design you are building, many of these older designs are questionable.

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