JOWITT MKII POPPET VALVE STEAM ENGINE
By Jason Ballamy - Part six
JOWITT MKII POPPET VALVE STEAM ENGINE
By Jason Ballamy - Part six
At a shade under 24mm dia the piston will come nicely out of a piece of 25mm or 1" bar so pop a bit in the chuck with enough poking out for the part and turn down to the required 23.95mm which will leave a little room for the piston to expand due to the heat if you decide to run on steam.
At the same setting the end can be faced off then starting with a spotting drill most of the waste can be drilled out to say 12mm before changing to a boring bar to open up the hole to the required 16mm dia by 24mm depth.
You will notice that I cut three grooves as per Stan Bray's sketch but two will be quite adequate and is what I have shown on the drawings. My engine runs fine on air with just one ring in the groove furthest from the crank.
O-Rings
I used Vitron O-rings: 19.6mm ID x 2.4mm section, bought on e-bay # 371503929586
Wrist Pin
This is just a short length of 4mm silver steel (Drill Rod) faced to 21mm long and with a 2mm dia x 5mm deep hole in each end.
Wrist Pin Pads
These can be from Acetal, nylon, or any other similar material or bronze if you prefer doing them in metal so long as it is softer than the iron so they protect the bore from the wrist pin. Turn a short length to 4mm and then the 2mm spigot and finally part off to give a 1mm thick head.
Conrod
I used a piece of 12x25mm black mild steel bar for this a few mm longer than the finished size. Start by machining one end down to 10x22mm and then the other to 6x10mm, square off the 10x22 end and then drill and ream 6mm dia 80mm from that end.
Big End Bearings and Keep Plate
I will describe these together as some of the work can be done on both at the same time.
For the bearings machine two pieces of bronze to 6mm thick and then soft solder together, once cool machine the pair to the final 22mm x 12mm. I find it easier this way than trying to line up two pieces that are finished size when soldering.
The keep plate is just a piece of 3mm thick material machined to 10mm x 22mm.
Drill the 3mm holes and include another small center drill hole in the keep plate.
Small End Bearing
This is a straight forward turning job, the bearing can be pressed or Loctited into the conrod.
Finally, thread the ends of a couple of bits of 3mm rod and add a nut each end to hold things together. Test the fit on the crankshaft as the bearings may have closed up a bit when the solder was cleaned off, if so just run the reamer through again.
Part one here Part two Part three Part four Part five Part six Part seven Part eight