Stuart 10V

Hello Scott, sorry I'm a bit late to this thread, only just seen it. To answer your question 'has anyone else come across the 11/16 vs 5/8' issue, the answer is yes I did earlier this year. I am new to Model Engineering, this was my second engine and I had the same dilemma, so I decided to make machine the base casting and bearings and measure the width between the inner faces, and found it to be 11/16 as per the pic below (bit of interpolation needed!). I then made the crank to the 11/16 dimension, it was a tight fit between the bearings and needed a little easing. I would be interested to hear how you got on with this. I finished the 10V a few months ago, and am very please with how it runs (on steam). I have now bought the reversing gear which which I will tackle after my current project, the Stuart Beam which I am currently half way through. Steve

Ah! One must first determine what "the job" is! The desired result is a smooth moving piston with minimal friction that seals. To do that you must know what ACTUAL dimensions you are dealing with. I.E. ACTUAL bore diameter, ACTUAL O-ring X-section diameter, and desired O-ring compression I have found that 5% compression is the upper limit of compression. If it were me, I would shoot for a for no more than .005" total compression. For example: Assume a nominal bore diameter of .750". Assume actual bore diameter = .753". Assume nominal 3/4" x 1/16" (.0625" 0-ring will be used. Actual measured x-section = .071". Desired 0-ring groove diameter would be .753" - 2x.071" + .005" = .616". If you noticed, There is no need to know the piston diameter as it obviously must move freely. The o-ring groove depth has no meaningful relation ship to the piston diameter. Groove width is not so critical. It needs a bit of side clearance. Using published O-ring compression numbers will most likely result in far too much drag. Rick

Stuart 10V

Hi,

Would brass be a suitable material for the piston and valve rods for the Stuart 10V?

Scott.

Probably be lower down the list than mild steel, why not just get some stainless steel, 303 is easy enough to work with.

I've got a 10H on my to-do list (1950's kit, my son found it when clearing out very dusty attic). Will this have a similar problem, or did it just affect the 10V ?

As the OP's problem was a difference between the Stuart drawings and the 10V book I assume you won't be using the book so no problem.

True, for some reason I thought they shared the same book.

Old drawings certainly have all the options on the same sheet, I've not actually got the book but think it only covers the vertical 10 V though most parts are the same between the two engines including space between bearings and the bearings themselves.

Hi,

I am ready to start machining the eccentric strap for the Stuart 10V. Is there anything in particular I should be aware of/watch out for? For example I notice the arm of the strap is cast slightly off centre to the main bearing end that locates the eccentric sheave.

Scott.

Just be aware that the “Gun Metal” is very malleable and easily distorted, so clamping methods are critical. A good portion of the work is hand work, so just take your time. The part is more delicate than it appears, but not overly challenging.

The 10H has the same part, just longer.  If you plan to add reversing, you might want to hold off on the eccentric strap since this one would not be used. 

Edited By Django on 21/09/2023 13:16:23

Edited By Django on 21/09/2023 13:22:23

Edited By Django on 21/09/2023 13:22:55

Most Stuart eccentric starps were/are hot brass pressings, not sure of the very latest but they may well be part CNC machined brass the same as the current conrods are but not gun metal..

I'd try and layout the hole inline with the actual rod and see if there is enough material either side to get the clamping bolts in, you could even leave th ebolt out on the solid side as it is only decorative the one on th esplit side is what adjusts the fit.