Part built Allchin 1.5 inch

Evening all.

Well I’ve gone from proud to feeling very sad and stupid, looks like I’ve ruined the cylinder after all the work.

I had to chain drill and Dremel and file steam ports as I have no milling machine, however in doing this it’s not as accurate as it should be and the middle two section is thinner than it should, the separating splines for a better work should be 3/32 but mine come in at 2mm each, add that to the undersized 1/4 hole and my valve when sat in the middle covers exhaust and leaves open the side ports by half way.

Looking at the drawing and what I can others have done this valve when central should cover exhaust and the side ports but only allow steam into the valve steam space.

The way mine is steam could get down the side ports as my valve hangs over them half way each, I feel abit sick and disappointed in myself today.

Only thing I can think of is to get someone to machine a slide valve in the future with a thinner exhaust space so that it will only cover exhaust port when central, but not sure even that a fix, one positive is the width of all three ports together is correct st 15.87mm this part is fine, but the two spacing being undersized has left less material for the valve to sit on when central.

Edited By derek blake on 30/01/2019 19:13:49

Edited By derek blake on 30/01/2019 19:21:32

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Many thanks Bill, everything I’ve posted so far has been on lathe or hand filed this is really the biggest mistake so far and it’s a real kick in the teeth after such effort.

Your right I hope Jason does have an idea, I’m hoping a new valve will save the cylinder being scrap.

Regards

Derek

I'll stick my neck out a bit but I suggest that your error won't be too serious. If the distance between the outer edges of the 2 inlet ports is correct, then basic valve timing will be OK. What you will have is a narrower sealing land between inlet and outlet ports, which might allow a bit more live steam to pass directly to the exhaust. This is not ideal, but not a show stopper.

Others might see it differently.

Hi Clive

Thank you for your response, hopefully you are correct and it’s still useable. What I’m thinking is if I made a new valve with more material left and thinner exhaust port this would mean that the two side ports wouldn’t be exposed like they are now.

Derek,

Don't panic Mr Mainwaring!!! Don't panic. As the overall distance is fine the timing of inlet steam will still be OK (it does look as if the valve has quite a bit of steam lap though). The lap of the valve is the amount the valve overlaps the ports (steam or exhaust). Some engines have a positive lap on the exhaust cavity which leaves a cushion of steam in the cylinder at dead centre but many have negative lap on the exhaust (more commonly termed exhaust clearance). I am sure Jason being very CAD literate and a nice chap could knock up a drawing to asses the impact of what you have now and whether you really need to adjust anything. You will need to give him some decent dimensions though. Overall length of valve (across the ports) the distance between the outer edges of the steam ports, the width of the steam ports, the width of the exhaust port and the size of the ligaments as a check. Overall designed valve travel would be helpful too (throw of the eccentrics would be close enough). I am afraid I am a CAD dunce so it would take me a lot longer to work out than Jason. You could also mock it up in a valve simulator to get an idea of what the effect would be but I struggle with them as well lol.

Paul.

Derek, post the 5 sizes of the ports and gaps and I'll see what size valve cavity would work best with them.

Another option would be to mill out a recess over the ports and let in a plate with the right spacing, though not easy without a mill.

Hi Jason

Please could you confirm what you need, the overall width of port face with the drilling’s is 15.87mm as per drawing.

The side ports are 2.75mm wide appox, the vains or strips of material down the middle are 2mm wide each instead of the required 2.38mm

The central exhaust port is 6mm instead of 6.35mm.

The width of steam space on valve should be 29/64mm but mine is 11.64mm and I didn’t touch that part it’s from casting so I hadn’t cleaned it up yet.

I’m not sure I’ve given what you ask but ask me what you require.

Many thanks

That's what I needed the size they have come out at, I have the original drawings.

Thank you very much for taking the time everyone to help me.

Think i have got a cure, will post in the morning. But if you want to post the exact 3 opening sizes as you have the overall an dtwo dividers I'll tweak my drawing to suit.

Edited By JasonB on 30/01/2019 20:53:01