Seagull Engine Construction Diary

Making a 10cc twin 4-stroke to the E T Westbury design


2021-01-21 – First light

The engine ran for the first time today.

2021-01-22 – Early testing

A short early run. The engine is motored by the lathe via a sprag clutch (a form of freewheel) so that it can outrun the lathe, and a torque limiter to protect the engine in case it decides to seize up.

It took a while for the engine to lift fuel. The carb is still a long way off - too lean when open and too rich at idle. It also looks as though the choke will be needed, as I had to open the jet before the engine would start, and then screw down again as it warmed up and before it would run well. Once it was warm, I did not try to go to full throttle, I won't do that without a load. I have yet to learn how the engine wants to be asked to start.

The main difficulty is that circulation in the thermo-syphon cooling is hopelessly inadequate. After a couple of minutes running the cylinders are too hot to hold. I shut down this run immediately when I saw a bubble in the water outlet hose. I was expecting I would need a water pump, but not expecting the engine to heat up so quickly. I have a pump more-or-less designed.

At higher speeds the exhaust is blue, so the splash lubrication is working. There may be a bit too much oil in the sump, and hopefully the piston rings will bed in. As a precaution I might strip the engine down to check all is well before it gets much more running time. I think, and fervently hope, the horrible chirruping noise is coming from the cheap double-hooke-joint drive between lathe and engine.