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Stuart S50

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Mike Bondarczuk02/04/2014 17:33:57
91 forum posts
6 photos

Hi to all,

Embarking on a Stuart S50 build and armed only with enthusiasm, an ML7 and a small mill and a huge gap in knowledge, so here is no doubt the first of many questions.

I am following Tubal Cains "Sally" build guides as in Model Engineer 1992 and have a question about the location of the three holes on the bedplate for the cylinder.

I have followed his instructions and find that these holes appear to be too far to the right of the bedplate, so am asking whether his dimension of 5 7/16" from the centre of the axle to the middle hole location is correct.

I am attaching a photo in which it is possible to see the scribe marks for the three holes and the furthest to the right just does not seem right.

How critical is this 5 7/16" and is the eventual distance between the piston travel and the axle a fixed distance or can to be varied to suit the casting.

Any suggestions are most welcome.

With thanks, Mike

bedplate 2.jpg

Dismaldunc02/04/2014 21:27:34
91 forum posts
8 photos

Hi Mike

Sent you a PM


thomas oliver 204/04/2014 23:45:03
104 forum posts

I have an S50 assembled from a Stuart Turner kit and have checked the dimension which does appear to be 5 7/16ins. I also have a part complete one marked out and the marking appears exactly as yours. It would appear that the bosses are not too well positioned.

GaryM06/04/2014 11:30:25
314 forum posts
44 photos

Hi Mike,

I thought the same as you, that they didn't line up with the pads very well.

If you haven't drilled it already, here is what I did. I left the hole nearest the crank in the same location, moved the second hole (valve side) 1/16" nearer to the crank and moved the third hole (farthest from crank) 1/8" nearer to the crank. So that would make the 5 7/16" dimension to the centre hole 5 3/8" and the other two holes 7/16" from that rather than 1/2". Pics below, you can just see the original scribe marks.

Having said all that I've not got it running yet due to "essential" decorating of hall, stairs and landing. wink

Hope this helps.


cylinder drilling.jpg

cylinder drilling under.jpg

cylinder drilling cyl.jpg

Anthony06/04/2014 13:28:33
6 forum posts
3 photos

I built an S50 from castings and did the same as GaryM. I also put small pins in on the base pads at the sides of the bolt holes as suggested by Tubal Cain. This really does help later on in the build, as the cylinder is always held in the correct position whilst the bolts are tightened up. Good luck with your build.

Mike Bondarczuk06/04/2014 15:20:38
91 forum posts
6 photos

Hi Gary, Anthony and everyone else who offered advice,

Many thanks for the valuable information and as of yet I have not drilled any holes but with your advice now know what to do.

Will post more pics as I get to grips with the final marking out again.

With thanks,


Michael Edwards 101/01/2019 16:34:23
59 forum posts
46 photos

Hi All I know this is an old post but I have just received a Stuart S50 for Christmas off my children and starting to machine it. I have machined the cross slide and the cylinder mounting points on the bedplate but cant markup for the holes. I have attached a photo showing the issue I have. According to the articles by Tubal Cain you use the approximate center of the crank bosses to measure the 'A' axis and use this as the datum but when I come to measure anything on the 'B' axis im lost to what to use. As I cant take a measurement from the edge of the casting because that is not square. Any help appreciated in advance



Edited By Michael Edwards 1 on 01/01/2019 16:35:45

Edited By Michael Edwards 1 on 01/01/2019 16:36:22

Edited By Michael Edwards 1 on 01/01/2019 16:36:41

JasonB01/01/2019 16:49:41
19506 forum posts
2131 photos
1 articles

I would set the cross head guides to run as straight (Vertical in photo) as possible and then find the ctr line between the two of them. From that you have the ctr of the cylinder so can set out it's mounting holes. Set the sides of the bearings from this ctr line too but if you can't get things to fit then the far left is not critical and if the the right side does not work out then adjust the crank web width to suit.

Michael Edwards 101/01/2019 17:11:40
59 forum posts
46 photos

Thank you Jason.Will crack on with that now. Regards Mike

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