The 'perfect' Stuart Turner...

[gondolier88]

Hello everybody,

Let's say you had just acquired a very well run-in example of a Stuart Turner 5A, a very well made example, made to the drawings with all from Stuart castings.

It performs as well as any 5A out there, however, therein lies a problem; 5A's are noisy, short-legged, unreliable reversers and have the smallest bearing areas that you could get away with on an engine designed for running at the designed RPM.

If you had the engine in your workshop and were willing to put the time in to make it an all-round better engine, where would you start?

Hypothetical as the question may be, the answers may inspire me to crack on and get some suggestions in motion...

Greg

[cyberbadger]

I find myself that the Stuarts that are all dressed up with lagging, brass and copper and noisy stephenson reversing linkages probably never actually did a darn bit of actual steam service.

I bought a few small engines including Stuart and PM Research.

I sold a fancy 4a all dressed up, nice little "model". Looked pretty, in every respect, but the tolerances, not so much.

The proof is in the pudding if you actually want a little Stuart to do a job.

The Stuart Turner engines are VERY VERY well balanced for a small steam engines.

I kept what I call the "Green Turner". (Painted green)

A good little engine that works.

Probably a little high strung, and the ratios may be off - but my Green turner purs and makes electricity!!
My video:
https://www.youtube.com/watch?v=9AbbH1R48X0

-CB

[Scotty]

This is a 5A - double size, 12.5 HP effective. It drives a 5 ton boat.
It runs now for 25 years, 19 years ago we converted it to piston valve gear.
Starting and reversing is absolutely no problem.
But it has been fabricated to a very high standard and extremely close tolerances.

Scotty

[gondolier88]

CB, Scotty

The engine has been doing lots of real work pushing a well used Frolic 21 around for the last 10 years or so http://www.steamboatassociation.org.uk/page-1117882 .

It has been worked quite hard, so the options are to go right through the engine, service/replace what needs and restore the engine back to new. Or the tempting option is to strip it right down (needs doing anyway), take out all the bad bits, design new parts to more sensible proportions, put them back onto the existing good bits and essentially have a pretty engine (which they are) that works reliably and without excessive noise and wear (which it doesn't at the moment)

The engine you show is really something Scotty- the valve spindle guide mounted lubricator is a nice touch! Interesting you mention the piston valve conversion as it's one of the things at the top of my 'wish list'.

My thinking so far;

1- Convert HP Slide Valve to Piston Valve
2- Redesign Stephenson's valve gear to better geometry, with much larger bearing surfaces, aided by...
3- Increasing the distance from the bottom of the cylinder block to the shaft centreline which would require...
4- Longer con-rods...
5- Longer (hence shallower) valve gear

All things being equal it should make for a better proportioned, lower-revving, higher torqued engine with better valve events.

Greg

[Scotty]

Hallo Greg,
do you want drawings of the modified/enlarged 5A ?
You could scale them back to original size.

Scotty

edit: we had run this engine with > 800 rpm (no load).
Service speed is 350 rpm.

[gondolier88]

Scotty,

That's very kind, but I must admit I have just realised I made a huge typo' in my original post- the engine I have is the 6A- compound, not the 5A single!

That said if you have any drawings I would be very interested, especially the piston valve conversion as the 5A and 6A are very similar in detail, even if dimensionally they are different.

Sorry for the confusion Scotty, thanks for your help!

Greg

[Scotty]

Hallo Greg,
please send me a PN with your postal adress then you will get the piston valve drawings within two weeks.
I have to copy first, these were the last drawings I did by hand.
But be prepared, it is not a simple operation.

Scotty

[gondolier88]

PM sent, thanks Scotty!

The link above doesn't want to work for some reason- click on the letter 'B' and scroll down to 'Bruin' to see the boat the engine came out of.

Greg