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Half Scale Domestic "Stovepipe" Hit & Miss

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I'm sure some of you would have been following this one over on HMEM, if not the early part of the build can be seen here where I left off by machining the piston, so next up was the piston rings

These were turned from CI bar, parted off and then split with the cutters you can see in the photo before being spread open and heated to red heat for a few mins.


Next up was the bronze conrod, the drawings have a note to make this a little shorter to reduce compression so the hole does not fall ideally in the middle of the boss which means a bit more clean-up work but nothing too difficult. First I took a light skim off each side to give a ref face and something decent to mark out on.


The casting was then sawn in half with a hacksaw and the two mating faces flycut back to the lines

The two faces were then tinned with plumbers soft solder and then sweated together, this way there is no risk of the parts moving while drilling for bolts and machining.

I set the rod up on packing and bored the big end, followed by the small

The holes for the fitted bolts were reamed and flats machined each end, with the added security of the bolts the rod was mounted onto an expanding mandrel and the sides finish turned.

It was then just a case of several milling opperations to get the big end in particular to the correct shape.

And here it is fitted to the piston.

Next I tackled the carb. The top is turned from 1" brass bar and then transfered to the mill to have the hex formed

before being upended to have 4 holes drilled which are quite a tight fit against the small pip in the middle.

Luckily the bronze casting for the main carb body has a large turning spigot incorporated which makes it quite east to hold so most of the turning can be done at one setting, then moved to the hill for the cross holes and also two rather tricky passages for the fuel.

I then machined a matching 1/2"x40 ME thread onto a scrap bit of stock so the bottom hole could be reamed and undercut. I used the same method to hold the body to drill & tap the fuel needle hole at the required angle.

A couple of plugs for the fuel passages were turned from the machining spigot and then silver soldered into counterbores at the ends of the passages, the bits of angle stop the plugs dropping out when soldering, still a bit hot here.

And here are the two parts after a quick clean up, the plugs now need filing to profile and the surface texturing to match the rest of teh cast body.

The remaining parts are mostly straight forward turning if a little bit on the small side, the main thing to get right is the 45deg seating for the "float" which need s to be lapped in so the fuel is shut off until there is a vacuum in the intake at which point the float lifts against a small spring and allows fuel to flow.

And this is how it all goes together.

It was then just a case of making up the fuel lines, intake pipework and fuel filler pipe & cap.



Looks absolutely spot on this Jason. Still have a thing for stationary engines so love big i.c. models that are of actual engines!

Nice 1.


Hi Jason

Good to see a continuation of your build.  Will be following you along the way.


Dave G:
Hi Jason, I am enjoying your build as I have 2 of these awaiting me to be built. Thank you for sharing, Dave

The exhaust valve and timing are actuated by a gear driven rod that passes down the side of the engine. I used a length of 1/2" presision ground mild steel for this, the gear is supplied in the kit and the rest of the parts are basic turning and milling - from left to right.

Exhaust cam
Timing collar
Corian Insulator
Cap retaining bolt

The other end of the rod is supported by a bracket that bolts to the cylinder head. There are 4 holes that lie on the same centreline, the best I could get was the three small ones in line and the large bearing hole slightly off.

This would have been OK after cleanup had there not been about 1/16 of shift between the two halves of the casting, you can see the step on the left of the photo

Which resulted in the hole on the other side being a bit off :(

I got round this by mounting the casting on a mandrel, turning down the boss and then loctiting a brass sleeve in place, once painted it won't show.

The timing can be advanced and retarded by a lever that is another bronze casting, this was a bit of a pig to hold, first thing was to get a flat face

I could then get it on the rotary table to bore the holes and cut the curved slot.

Final job was machining a recess on the back

And thats the leaver finished with a few of the fittings, the contact at the bottom is held in two bits of corian to insulate it from the engine and this makes contact with the timing collar to fire the sparkplug. The spring pulls the governor trip off the catch

The last of the bronze castings is the exhaust rocker, no machining pics of this just the finished item.

One other item that fits onto the bracket is the governor trip this is fabricated from drill rod and ground flat stock as is the catch.



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