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The shift arm is another built up and machined out part. Start by turning a hub and laying out the arm. The shift arm has a nice taper and rounded portion for the clamping nut. Set up a little jig to mill the taper. Mill the taper on one side, then flip over and do the other side...

The rest of the linkage parts or brass and silver solder fabrications. None of them are particularly difficult. Just have to get them all done. The reach arms are 3 pieces. Two arms are required. The spigots on the boss ends are rather under sized. When the final assembly is drilled out the...

Hi John: I built a #4 couple years ago and had the same issue. I recalculated the valve events. I don't think cast iron soft solders. It silver solders tho. vr Bob

The radius link is a very interesting part to make. My son and I have learned a CAD software for use on his 3D printer. FreeCad is the software we use. It’s a free download, although the author asks for a donation. There are 100’s of FreeCad tutorial videos on YouTube. A handy feature of FreeCad...

The eccentric rods are a 2-piece brass fabrication. It’s possible to whittle them from solid, but that’s kind of wasteful. Mill out the rod arm and saw the slot for the radius link. The cylindrical end of the rod arm will eventually become the spigot to match the eccentric strap. Make that...

I bet those rods are threaded with British Association (BA) threads on both ends. Unless you have BA dies, you'll have to change out a number of other parts. Maybe contact Stuart to see if they have just the replacement shafts. Andrew at the sales email is a good guy, he'll get back to you.

Grade 303 is the best for machinability. It is available "ground and polished" from McMaster Carr. Very precise in dimension and smooth. Won't wear out packing.

The eccentric straps are cast iron bar stock fabrications. Cut and mill two slabs to final thickness. Clamp both pieces on the mill table and machine together. Square the slabs to final width, but extra in height. Eventually the slabs are sawn in half, so leave some extra stock. Saw the...

Time to machine the Stevenson eccentrics using the custom stub mandrel from last time. Chuck the stub mandrel in the four-jaw and center one of the eccentric lobe centers. Fix the eccentric blank to the stub a screw and washer. Turn the first eccentric to final dimension. The key in the...

Super nice work. From your descriptions and photos I think I could take this project on. The method you used for the crank answered a lot of questions.

With the math done and verified, time to start on the eccentrics. The basic engine plan calls for the single eccentric or the slip eccentric collar be fixed to the crankshaft with a grub screw. Makes for an easy adjustment. The 5a Stevenson plan calls for the eccentric to be keyed to the crank...

Let me know if you can't find your drawings. I'll share mine. Bob S

Hi packrat, here we go!! Today is the start of the Stevenson reverse for the Stuart 5a engine. The basic 5a engine plan includes two types of valve mechanisms. One is a single fixed eccentric, and the other is a slip eccentric. The plan for the Stevenson is sold separately. Stuart sells a...

The valve chest, valve and valve spindle are next. I did not take a whole lot of pictures on this because it is all straightforward machine work. Nothing remarkable. The packing gland for the valve spindle is the same general design as the cylinder lower cover. It involves a ½” British Standard...

Back on the cylinder with some work on the portface. Use parallels to set the portface horizontal to the mill table as closely as possible. Mill the portface clean and tap the bolt pattern for the valve chest. And then there was trouble. There is a difference between 1.250 and...

Starting on the cylinder today. The Stuart 5a cylinder casting is wonderful. It is spot on in dimensions and is wonderful to machine. The steam ports and exhaust are right on dimension and very sharp. The cores are clean and uniform all the way thru. No work at all was needed on any of that. The...

Today are the top and bottom cylinder covers. These are a fairly straight forward turning process. The covers are cast iron, with no cast bosses to help in the turning process. However, there is enough material to grip during the machine steps. As with all the other castings, they are way over...

Next for the piston rod is get it between centers with the dividing head to shape the crosshead portion. Mill the crosshead to the final width on both sides. All of the nice-looking cast features on the crosshead are gone. Start profiling those shapes back in. Work the lower end and side...

The piston rod and crosshead are one single casting. As with many of the castings, this one is way oversized. The casting has a very nice profile, but it will all go away during machining. I’m not sure what Stuart uses for the connecting rod and the piston rod castings. It turns like some kind...

Today is a short update to finish the connecting rod. Round over the end of the con rod on the rotary table. Center the rotary table directly under the mill spindle. Clamp down a slab of aluminum and drill for a 3/8” pin. Secure the connecting rod on the pin and round over the end. The rotary...