By Roderick Jenkins
M4. C4n
I designed and built this more than 20 years ago.  Overhead valve designs generally give more power that side valves but one disadvantage is that they tend to be very tall. The idea of this design was to make a compact 4-stroke engine with good power. The Ricardo style head allows a higher compression ratio than conventional side valve designs. Capacity is 10cc (.61 cu. in.) and is a short stroke, over square design.  Mostly made from unspecified aluminium alloy bar stock (almost certainly HE30) but the cylinder is mild steel.
The piston has a single cast iron ring.  The con rod is high tensile ally (H15 over here)
The crankshaft is turned from a large HT bolt with a pressed in crankpin.  Balancing the short stroke piston was helped by these two heavy metal inserts, density is about 18 compared to steel at 8 and lead at 10 (I wish I had a source to buy small quantities of this stuff - I got this from the surplus market)
The cylinder head is a Ricardo type and the design compression ratio was 8:1.  I offset the glow plug over the inlet valve with the idea that the valve would protect the plug from the incoming mixture and help to prevent it quenching.
The cams are pretty fierce.  They are pinned to the gears with a 12 BA screw.  The 3 screw holes are spaced a whole number of teeth plus 1/3 apart so that there is the potential to adjust the timing in fine increments.
I cut the gear teeth using home made cutters.  I made these 30 degrees pressure angle because the pinion is relatively small, though at 15 teeth I'm not sure this is actually terribly important.
The current carb is my trusty Matador model (as used on the Wyvern) but I have a custom one that needs completion.  She's a pretty temperamental beast.  It took me all week to get her started with new valves carefully ground in and the cylinder top and head lapped with fine wet'n'dry.  She likes the throttle wide open and a good squirt of fuel into the carb.  And I need to find a better way of clamping her to the workmate.  I called her Scaup after a species of duck - I don't think that's been used before for an engine or plane (I wait to be proved wrong).

Poster prepared for the Guildford Exhibition. Click on poster for larger version.