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The main chimney is a simple job from 10mm OD aluminium tube, thread one end M10x1.0 for a length of 22mm. Face to length and form the 9mm dia spigot on the other end. I used slightly larger OD tube so had to machine it down to overall diameter.

The base is just some 12mm stock drilled to 9.0mm and tapped M10x1.0 with the upper edge rounded off.

The top ring can be turned on the end of some bar and if you put a parting cut part way through so the bead can be easily shaped, the drill will part off the work as it breaks through.

The parts can be assembled with a drop of Loctite 648 to hold the ring in place, make sure you have no more than 2mm of thread sticking out the bottom otherwise the exhaust passage in the base will be restricted.

And a quick test fit.




Part 7 by Jason Ballamy


This could be turned from a length of 10mm aluminium 6082 but I had a lot of 1/2" (12.7mm) so used that.

Cut off a piece about 20mm longer than needed, face each end and put in a small size 0 centre drill hole. Reduce one end to 8mm dia and the other to 10mm if using larger stock.

Now holding the rod in a mill vice the two holes can be drilled and reamed and the ends flattened off.

Back to the lathe hold the 10mm end in a collet or 3-jaw and offset the tailstock to form the taper, I used a small live centre in a boring head to get the offset rather than disturb the setting. You could also set the top slide to an angle if preferred. Do the final cut with either a small HSS tool with a rounded end or an insert tool like I used in the photo to give the fillet where the round rod joins the flat ends. Do take it easy as the rod is getting quite thin at this stage but will be nice and light.

The two bearings are simple turning jobs from a bit of bronze bar with reamed holes. I find the mill vice is quite good for pressing them in, use a spacer on the big end so the bearing can protrude evenly both sides. If your fit is a bit loose then high temp Loctite such as 648 should hold the bearings in place.

This is the finished rod together with the gudgeon pin block and piston described earlier

Part one here  Part two  Part three Part four  Part five  Part six Part seven Part eight

Part nine -

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