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Stuart S50 - advice needed regarding valve/steam chest assembly

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TiddlerTad10/07/2018 09:59:40
54 forum posts
2 photos


I'm a novice and building my first stationary engine - a Stuart S50. Very enjoyable so far!

I'm following Tubal Cain's Model Workshop series (one of the reasons I chose the S50) and have got to the point where I need to transfer and drill holes from the chest cover, into the chest and through to the cylinder. The bosses on the chest are offset and, from what I can gather from Tubal Cain, they are offset towards the cylinder side. However the assembly diagram that came with the kit seems to suggest that the bosses are offset towards the cover. I think the assembly diagram isn't 100% accurate, or maybe it's just the way it appears in print.

My guess is that the bosses should be offset towards the cylinder, but I need to be 100% sure before I start drilling.

Can anyone confirm which side the bosses are offset towards?

Many thanks in anticipation.


Edited By Andrew Whale 1 on 10/07/2018 10:00:46

Edited By Andrew Whale 1 on 10/07/2018 10:20:50

Gas_mantle.10/07/2018 10:41:51
359 forum posts
269 photos

Hi Andrew, I haven't built a S50 so I'm no expert but can it be worked out by looking at the thickness of the slide valve and the nut that retains it ?

JasonB10/07/2018 10:44:45
18119 forum posts
1996 photos
1 articles


Easiest way to check is to look at the valve and nut. The part of the valve that does not have the nut slots in it is 1/8" thick. The nut is 3/16" wide with a central hole so 3/32" from the edge.

Add up 1/8" and 3/32" you get 7/32" and will also need a slight amount of movement so the valve can lift off the port face.

Now if you put the bosses for the valve rod closer to the cylinder port face that will only give you 3/16 to the center of the valve rod but you need over 7/32" so it can't go that way around.

With the bosses away from the port face you have 1/4" to plat with so that works out nicely for 7/32" and a 32nd for lift.

Chest drawing and valve parts drawing change the last number to get the rest of the articles 1-10

Edit. Peter posted the same method while I was typing all the details.

Edited By JasonB on 10/07/2018 10:45:52

TiddlerTad10/07/2018 11:49:27
54 forum posts
2 photos

Hi guys - many thanks for the super fast replies. Your logic is spot-on. I never thought to look at Part 9!

It looks to me like Fig 28 in Tubal Cain's Part 4 is therefore wrong - as it clearly states 'Top face' - in which case the bosses would be closer to the cylinder. But, maybe, I am misinterpreting it.

I'm really glad I sought advice on this and avoided a mini disaster - and I do really appreciate your help.



mechman4810/07/2018 18:10:43
2663 forum posts
410 photos

Just checked my S50; the valve rod bosses are biased toward the top plate, away from the cylinder, only just noticeable, so falls in line with JasonB's description.


TiddlerTad10/07/2018 18:28:29
54 forum posts
2 photos

Thanks George - I really appreciate you checking yours out for me. I'm also very pleased that it is engineered as JasonB thought it should be.

All the best.


TiddlerTad25/09/2018 15:32:50
54 forum posts
2 photos


Hi folks - just an update...

I managed to complete the S50. It runs really well on air and I am well chuffed. Gas_mantle is bringing his boiler over tomorrow to give it a run on steam!

Many thanks for the help and advice.


Edited By Andrew Whale 1 on 25/09/2018 15:33:22

Lainchy13/06/2019 09:42:09
244 forum posts
95 photos

Really enjoyed watching your series on this Andrew. I have now purchased a Chester DB7vs, and a Warco WM14 mill. Plenty of learning to be done, but hopefully getting an S50 at Warwick in October. I'm booked on Axminster's small lathe course in August, but looking forward to having a go.

TiddlerTad14/06/2019 10:08:45
54 forum posts
2 photos

Thanks Ian. I found the S50 a pleasure to make. I hope it goes well. I recently made a Stuart 10V, which I found more challenging. I made a series of videos on that too. Check out the following link: My YouTube Playlists

All the best.


Edited By Andrew Whale 1 on 14/06/2019 10:10:22

Lainchy29/07/2019 09:11:04
244 forum posts
95 photos

Cheers Andrew Subcribed and full notifications set. Enjoying the series on the half beam too.

TiddlerTad29/07/2019 10:33:46
54 forum posts
2 photos

Thanks Ian. I hope the Chester and Warco gear is working well. I think I've set myself a real challenge with the Stuart half beam!


Lainchy29/07/2019 11:12:33
244 forum posts
95 photos

I really does look a challenge too!

I've started on a small bar stock oscillating engine Andrew, but the S50 has arrived. I have the Axminster small engineering course in about 3 weeks... so I should be well prepared for the S50 as a project over winter.

Cheers Andrew,

Looking forward to see the half beam progress



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