Slide valve – which way?

[GaryMParticipant @garym]

[GaryMParticipant @garym]

Hi guys,

Finally managed to get my S50 running today (at long last they all say). However, I have a very basic question that I've tried to figure out myself without complete success. Which orientation should the slide valve have on the valve spindle. The first pic below is what I think is the correct orientation and the one that I used and it ran. Should it have been like the second pic? Just looking for confirmation. Most of you can probably answer this.

Thanks

Gary (now making swarf again)

[FMESParticipant @fmes]

first is the correct way Gary, with the lands of the valve being machined to obtain the correct valve opening event.

[Neil WyattModerator @neilwyatt]

Not immediately easy to answer, as it may run either way, as long as both admission ports aren't uncovered at the same time, but you will need a different setting of the eccentric.

Probably the top one, but without knowing dimensions of ports and valve cavity I can't be sure. It will effect events even if the cavity is square, as in the top arrangement you will get much earlier cutoff and more expansive working.

It may be that it runs better on air with the second arrangement, and on steam with the first

If the cavity is rectangular, the answer is easy as I think Stuart usually make the valve cavity the same width as the ports.

Can you show a picture showing both the port face and the valve cavity? Or give some measurements?

Neil

[GaryMParticipant @garym]

Thanks Lofty,

I thought that was probably the case. It is odd that the drawings and even the text from ME that I've been following don't actually tell you which way is correct and it will fit both ways. I couldn't try it the other way to see if the engine would run unless I filed the slot in the valve, although I suspect that it wouldn't.

Gary

[GaryMParticipant @garym]

Hi Neil,

You posted while I was replying to Lofty. Valve cavity is 9/32" x 9/32". Valve is 13/32" in one direction, 1/2" in other. Inlet ports are 7/16" to outer edges, 9/32" to inner edges. I would have posted a pic of the plans but camera battery has just died. I'll post one later for info. It might help other beginners to visualise it.

Gary

[Neil WyattModerator @neilwyatt]

Hi Gary,

As Lofty say, the top one, otherwise there will be a time when both inlet ports are open, rather than both closed.

Neil

[GaryMParticipant @garym]

Yes Neil, they were both open with second option. Unfortunately this wasn't enough of a clue to a newbie.

Gary

[thomas oliver 2Participant @thomasoliver2]

Instructions from Stuarts — First set valve for equal port opening. Place piston on top dead centre. Loosen eccentric on shaft and rotate in the direction the engine is to run until the port is just cracked open, then lock up grubscrew.

[Neil WyattModerator @neilwyatt]

> just cracked open

By "the thickness of a tram ticket" – a bit hard on those constructors in Edinburgh.

Neil

[GaryMParticipant @garym]

Hi Thomas,

Thanks for the reply. There is even more detail in the article from ME that I've been following, but you can follow those instructions with both orientations and still not know which is correct.

I think Lofty and Neil have answered the question. For the sake of completeness for others who may read later here are the drawings.

Gary

[JasonBModerator @jasonb]

Its all explained here, the 1/2" is the critical dimension , so number 1 is correct.

If you play with the PDF numbers you will get all 10 parts 1-10

 

Edited By JasonB on 24/05/2014 20:27:39

[GaryMParticipant @garym]

Thanks Jason.

Those are the articles I've been using, obviously it wasn't clear enough for me . I had assembled it as in first pic and it ran and then I had doubts that it might be the wrong way round.

Gary

Edited By GaryM on 24/05/2014 21:09:49

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