Stuart Turner 7a restoration project

[half whitParticipant @half-whit]

Hi All,

I recently bought this stuart 7a engine which I plan to restore to its former glory.

I would  guess that it is around 50 to 60 years old and has not been run for a long time.

As you can see it is all complete and looks very much like it has sat neglected in a shed for many years.

Despite that after a little tweaking and few drops of oil l got it running.

Having dismantled it there are numerous issues which I will document in this thread. I do hope it proves of interest.

Cheers for now

Geoff

[JAParticipant @ja]

I would guess it is well over 60 years old. I started mine as an apprentice in 1967 and finished it in retirement about 12 years ago.

 

Asking a few questions:

1. Are the brass colour nuts and screws actually brass?
2. What is the large hexagonal brass thing on the cylinder cover?

I will follow your adventures.

JA

[half whitParticipant @half-whit]

Hi JA

That’s a really well finished engine, I hope mine looks that good when I’ve finished.

I also intend to fit reversing gear as you have.

Your questions, the nuts are not brass they’re painted yellow,  same as the flywheel. The hexagon on the cylinder is just a brass screw, presumably to remove for lubrication.

Geoff

[half whitParticipant @half-whit]

Hi All,

Ok I’ve spent enough time looking at this time to get the ball rolling.

After removing the standard from the sole plate I discovered that one of the studs  was just a dummy as there was a broken 3/16″ whit tap in one of the holes. After some thought I decided that for this application to chain drill around the hole to remove the tap (see drawing). This made it easy to chip at and fracture the cast iron around the tap. The rough edges were removed with a dremel for and 3/8″ c.i. plug jb welded in place. A new hole has now been drilled and tapped.

Moving on to the valve chest next where I’ll have some questions for the forum.

Geoff

[JasonBModerator @jasonb]

The use of Whit threads makes it a fairly old model as they have been BA for as long as I can remember.

[JAParticipant @ja]

The drawing that came with the reversing gear bits from Stuart Turner is dated 25/1/54. The fixings are called up as BA.

JA

[half whitParticipant @half-whit]

Thinking about the age of this engine I’m inclined to agree with JA that it’s probably over 60 years.

The threads are all b.a. with just the standard to sole plate studs b.s.w.

The piston has a 5/32″ wide ring which is wider than the rings currently offered by S.T.

The drain cocks also may give some age clue with their horizontal handles, not angled upwards?

But how about this recess in valve face, chiseled by hand which take some of us on here back a few years?

Geoff

[noel shelleyParticipant @noelshelley55608]

The chiselled edges to the recess in the slide valve could well be to fettle the hole to give sharp edges. They were cast with the makings of a hole to start with. A much narrower piston ring would be good or if the bore is smooth even an O ring ? Noel.

[half whitParticipant @half-whit]

Hi Noel

That’s a good point, a cast start to the recess then edges sharpened with a chisel, that didn’t occur to me.

The edges are actually spot on at 3/8″ square and right in the middle of the face.

Geoff

[JasonBModerator @jasonb]

I’m not 100% sure on the 7A but Stuarts did the valves as hot brass stampings on the smaller engines so it could have been that rather than a casting. The eccentric straps/rods were made the same way. Now they have gone over to part CNC machined items.

If it is only going to be run for display then you can leave the ring out and get a nice slow tick-over, save it for if you or the next custodian want to make it do some work.

[half whitParticipant @half-whit]

Hi All, thank you for the replies.

At this time I’m reluctant to dismantle the piston and cross head assembly, time will tell but at present I’ll leave well alone.

The cylinder needs a repair to the port face where rust has built up in the valve chest and impacted on the face. Thankfully the bore is really very good and the piston is a close sliding fit with good compression. I think that face has been over machined as the metal is very thin adjacent to the inlet ports. The first photo has a black spot just above tip of the modelling blade. This a hole forming, and could easily be pierced with blade.

Anyway, photo 2 shows my repair, a cast iron with pre prepared port holes, jb welded and located with 4 8ba csk. Head screws. Just need to lap the valve in and should be good for another 60 years?

Geoff

[noel shelleyParticipant @noelshelley55608]

Remember that the eccentric will now be further out on the crankshaft when reassembled. Noel.

[half whitParticipant @half-whit]

Hi Noel,

Yes you’re right it will be further out but as mentioned in an earlier post I intend to add a reversing mechanism.

The new cast iron face is 1/8″ thick. This effectively moves the centre line of the valve rod further out by the same amount. With the eccentric in it’s normal position the centre line of the rod will be on its outer edge. This perfect for when I add the second eccentric the centre line will then be on the inner face of both eccentrics. I like this arrangement which is the same as the reversing gear in Muncasters book page 69. The forks on each side will be identical, one left handed, one right handed but still the same.

I don’t like the S.T. arrangement where one fork is bent to shape.

Geoff

 

[JAParticipant @ja]

There is nothing wrong with a bent link in a Stephensons reversing gear. Bronze bends well without any difficulties. One of the problems with the Stephensons gear is that not all the forces line up with the links. There has to be at least one offset. In addition, to be pedantic, the gear used is not a true Stephensons gear where the fixed pivot for the expension link is in its centre, not at one end which was common practice on marine engines. All reversing gears are complex, very complex.

Going back to simpler matters, when machining the double eccentric I broke two casting. The third was much easier, I used mild steel. At present I am making a true metric Stuart Compound Marine engine as a one day a week project. Although I bought all the castings from a dead local model engineer’s estate the double eccentric will be mild steel.

JA

[Nigel Graham 2Participant @nigelgraham2]

An alternative eccentric detail:

NB: this does need sufficient wall thickness on the thinnest part of the sheave.

I am basing my steam-wagon engine partly on the ST design, partly on K.N. Harris’ modification to the Maid of Kent locomotive.

The eccentrics are separate, in cast-iron, cut from stock bar.

To simplify machining at cost of some extra work, I modified the central retainer.

Rather than try to turn two identical steps, machine the rim right across then groove it to match the strap.

 

The retainer is a split mild-steel ring like a circlip without the end ears, manipulated into place by hand. (It could just as easily be of brass. There is, or should be, very little side-load on it.) The ring could be cut from sheet but is more easily turned, perhaps from thick-walled tube. Ensure some radial clearance to allow the strap to close properly without the retainer binding.

Deburr and slightly round off all its edges. I rubbed mine down on wet-&-dry paper on a flat surface.

Cutting the split wide enough to accommodate a small brass pin in the sheave will stop the retainer from rotating round the groove, though it probably does not matter much if it does.

”’

The launch-link, suspended at the end, was also common on traction-engines, possibly for clearance reasons above the boiler, as well as slightly simpler construction. As with a marine engine these spend most of their time running ahead, so less efficient back-gear events are not so important as on a locomotive that has to run equally well in both directions.

[noel shelleyParticipant @noelshelley55608]

Geoff, Whilst the ST D10 has hot stamped eccentric rods, my ST D10 with reversing has the bent eccentric rod on one direction, easy as the rod is steel only about 1/16″ dia, the No1 with reversing has handed rods, well mine has anyway ! Noel.

[duncan webster 1Participant @duncanwebster1]

You can buy spring steel snap rings to use in Nigel’s suggestion. I’ll probably do it like that next time I have to make an eccentric, then you can finish turn to fit the eccentric, which is not possible with the usual grooved design

[Nigel Graham 2Participant @nigelgraham2]

Thankyou for the compliment, Duncan!

Studying the drawing, it shows a 1/32″ groove between the two eccentrics. I doubt that’s cast in, and I’m not certain it’s necessary except maybe for appearance. Though you’d hardly notice it, if you simply turn each eccentric to its full diameter that extra 1/64″ towards the other.

I think if I was making that engine from stock rather than castings, I’d use cast-iron for the sheaves as specified, but consider making them as separate items held together with two discreet countersunk screws from the rear, finished flush on both faces.

It’s not clear though from that drawing how they are secured to the crankshaft.

[half whitParticipant @half-whit]

HI All,

I am now in the process of assembling the engine to test the repairs/renovations before I move on to making the reversing gear. I’ll post a video when I have it ready.

IMO/FWIW whoever made this engine did a really good job. The valve chest has been over machined and the crankshaft was sloppy in the main bearings but other than that most parts the still have good running fits which have clearly stood the test of time.

Having partly assembled the engine I can now assess the the position of the valve rod in relation to a main crankshaft bearing, see the diagram. I find that I have a 1/4″ from the outer face of the bearing to the centre line of the rod. This was designed and not a coincidence and of course means I can position the two reversing gear eccentrics on either side of the line similar to the arrangement in the muncaster drawing. I would like to use eccentric sheaves supplied by stuart but will design and make the attached rods myself. These will be identical but of course left and right handed. Any advice on the design of the rods, diagrams/pictures would be helpful. Geoff

 

[JasonBModerator @jasonb]

I suppose you could make the straps from brass with a flat on the top to take similar steel “T” ended rods as per the Muncaster drawing but the head of the tee will be quite small maybe 5/8 x 1/4 so would need some small fixings

Another alternative would be to have say a 3/8″ wide protrusion out of the top of the strap and then mill a 1/16″ deep slot into that to take your flat steel rod and secure with a CSK screw.

Third option would be to cut the whole strap/rod from solid 1/4″ flat brass bar. This would have more the look of the Stuart castings bit rods could be left a crisp rectangular section.

 

I’d probaly opt for the slot, something like this

This is more the Muncaster type from my Fowler, just scale it all down a bit

 

[half whitParticipant @half-whit]

Hi Jason,

Thank you for your reply which has been most useful.

I agree with you on the second option, which looks great. Very neat and easy to make.

I’ll proceed and post details soon.

Many thanks  again

Geoff

[half whitParticipant @half-whit]

Hi All’

I have assembled the engine to test run it after the repairs to the port face and some necessary adjustment of the main bearings.

Sorry no idea how to post the video of it running but it’s on you tube and if Jason or another moderator would like to upload that’s fine by me.  You tube….An old stuart turner 7a steam model under restoration.

Hope it’s of interest and that will be all for a while on this thread from me. I have design work to complete for the reversing gear and a lot of refurbishment to do. Anyway gents have a good christmas and new year and see you all as soon as I make some significant progress.

Geoff

[JasonBModerator @jasonb]

You can just copy the url from your browser when viewing the video or copy the link that comes up when you click “share” below the video and simply paste that into a reply. Looks to be running Ok

[half whitParticipant @half-whit]

Hi All,

A long break but here we go again.

After some thought I decided to use Stuart eccentric rods. After all I am restoring and modifying a Stuart engine so it seemed appropriate to use Stuart parts? Not a clue at present how to machine them but I expect I’ll work it out when the time comes..

Most of the original main now cleaned and primed and assembled to test fit the reversing gear.

More to come in due course

Geoff

[half whitParticipant @half-whit]

One of the things I really like about model engineering is looking at a drawing and wondering how on earth I’m going to make that part. Of course it usually requires some detailed thought but eventually we find an answer, often a lot easier if we have well equipped workshop.

Geoff
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