by ianda217

I designed this engine to fit in a 1:5 scale Sopwith Pup I am designing. The design varies from the other engines I have done in that the cylinder heads need to be printed separately. This is due to the valve gear being too complex to easily allow printing of a simple, vertically split engine.

The crankcase / cylinder halves were printed on a Creality Ender 3 without supports and with only a skirt - no brim or raft. The inlet tubes were printed with the fronts facing up and with supports and brim turned on but with the support overhang angle set to 80 degrees to minimise the amount of support. The cylinder heads were printed with “supports everywhere” turned on and with the support overhead angle reduced to 70 degrees.

Pushrod rockers have holes to allow the insertion of 16swg piano wire (or 1.5mm carbon fibre) pushrods. The engine is designed to rotate freely on ball bearings. As printed, it is designed for 65mm O.D. bearings. In my case the engine runs on two 6810 ZZ bearings as shown in the CAD sketch.

The joining ring is glued into the front half of the engine prior to assembly and ensures good alignment of the two halves.

This motor is also a bit porky. All-up weight with piano wire pushrods is around 140 grams (5 ounces). However, most WW1 models end up tail heavy so a bit of extra weight up front never goes amiss. Scale detail trumps a lump of lead every time.