Stuart Major Beam Engine

[Chipmaster]

I have resumed work on my Stuart Major after a three month break partly due to working on an Alyn Foundry I. F. Allman engine. I'm working on the slide valve but there is a problem, the valve rod as drawn can't be fitted inside the valve / steam chest because it is too long. Fortunately some months ago Dave'Chipswitheverything' forewarned me and set out the solution he had used. 

Extracts from the drawings,


[url=https://flic.kr/p/2jiJy9i]

[url=https://flic.kr/p/2jiJEys]

Slide valve casting
[url=https://flic.kr/p/2ji6ctJ]Slide valve by Andy, on Flickr

The casting was large enough have a socket milled to accommodate the end of the valve rod and dispense with the 1/8" steel plate held on by 2BA screws shown in the drawings.

Milling the slide valve,
Slide valve by Andy, on Flickr
Slide valve by Andy, on Flickr
Slide valve by Andy, on Flickr
Slide valve by Andy, on Flickr

The valve rod, instead of 9/64" I used 4mm diameter stainless threaded 5BA on the outward end and a stainless steel lug silver soldered on to drive the slide valve.
Valve rod by Andy, on Flickr

Slide valve and valve rod by Andy, on Flickr

These two pictures demonstrate the problem,
Slide valve, valve rod and valve chest. by Andy, on Flickr

Slide valve, valve rod and valve chest. by Andy, on Flickr

How is the builder supposed to fit the valve rod inside the steam chest?

The solution is to bore and thread a large say 7/16" hole in the bottom of the chest so that the valve rod can be passed through the hole which can be sealed with a threaded plug. That's what I'll do tomorrow.

Andy

[simplyloco]

Thank you for that insight. A great help!
John

[Jasonb]

The other option would be to make the valve rod in two parts, drill and thread the plain shank to take a longer threaded section rather than have it all one length. Your rod looks to be longer than drawing, I make it that the unthreaded length is 1.657 which will fit into the 1.813 cavity.

That way you can fit the rod, push it up through the hole and screw in the threaded part, could even just do a plain hole and loctite the two together but you won't get it apart easily if needed.

If you do go for the plug option it would be worth making that to take a drain cock so you can get any condensate out of the valve chest if you are going to run on steam.

[Chipmaster]

Yes Jason the threaded section of my rod is considerably longer than specified because it came in handy having been a test piece when I set up a small Coventry Diehead to cut 5BA threads for my Allman exhaust valve rod. I’ll trim it to the required length eventually.
As I intend to run the engine on steam it also occurred to me that a drain cock would be useful beneath the steam chest.

Andy

[Alyn Foundry]

A wee " T " nut ?? 

[Chipmaster]

Yes Graham that was always a possibility too 
Andy

[Chipmaster]

To complete the valve chest I bored and threaded a 7/16" x 26 tpi hole in the bottom of the chest.  The lug on the end of the valve rod was ground down until it would pass through the 7/16 as the threaded end went through the gland at the top of the valve chest.

A brass bush 7/16" x 26 tpi was made with a 3/16" x40 tpi internal thread to fit a union cock for draining the valve chest.







The slide valve will require an hour or more lapping to produce an acceptable finish on the port face.

Andy

[simplyloco]

Excellent!
John

[Chipmaster]

Hello John, pleased we have another ST Major builder, I must get a move on.

Andy

[simplyloco]

No Hurry!

[Johnmcc69]

 
 Nice solution!

 John

[Chipswitheverything]

Hi Andy, pleased to see nice progress on the beam engine again, and the drain cock in the plug on the s' chest is a nice refinement, which ( if I ever get back in my workshop, still curtailed in that after so long ), I can think of adding.   Dave

[Chipmaster]

Hi Dave, sorry to hear you're unable to return to your workshop.

I have been working on the eccentric strap which is a gunmetal casting, here's an extract from the drawings,




I decided to start by milling and filing the casting in order to mark out the positions of the two 5BA clearance then drilled the holes 0.125" to be a snug fit for the 5BA screw. I then sawed the casting in half and milled the joining surfaces flat. The hole in the centre of the casting has a generous allowance for sawing and truing up the faces. Quite a bit has to be milled off to create a circular hole.





 
The two halves were fastened together ready for machining,



To bore out the centre I made a jig holding the casting with four 4BA screws plus nuts and washers crude and possibly dodgy but it worked.



So far so good.



Then mounted on a snug or mandrel so that the sides could be machined to reduce the thickness of the strap to 19/64".



The eccentric strap at the close of play today,



Andy

[simplyloco]

 Lovely job.
John

[Chipswitheverything]

Hi Andy, that's coming on well.  Seem to remember putting the strap on the little GHT rotary table to do the outside profile, also running a bullnose slot drill along the sheave side of the boss to blend the two shapes together. 
  Don't know if John, who is chewing over the prospective work on his Major, happens to have caught up with the forum write up that I did on my engine?, ( albeit still awaiting the finishing stages even now )  - my pics and write up are in my posts starting in March 2016.    Dave