Seagull Engine Construction Diary

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

Cooling System

I had intending a passive thermosiphon cooling system with an open topped tank piped to the cylinders. My ideas changed during the later stages of construction. The first test runs of the engine showed that a thermosiphon system would be hopelessly inadequate.

I want to achieve neat pipework with swept Y joints, and two-bolt flanges throughout. The manufacture of these pipes is covered in the Fabrications section.

2020-05-01 – Trying out the fan

Since last writing about the cooling, it has become more complicated. I have acquired a little radiator and fan, intended for cooling souped-up computers. The plan is to use a microcontroller for some limited engine management. The fan will be switched on and off, and its speed controlled according to a temperature sensor on the engine. It is a 4-wire type, having 12V positive & negative, speed control signal input, and tacho output giving two pulses per revolution. The speed control requires a pulse-width modulated signal at 25kHz (The high PWM frequency is to stop the fan in your desktop gaming machine making a nasty audible whine.)

This evening I wired up the fan to a 12V battery for the first time. The wires seem very thin. It is very quiet and does not push as much air through the radiator as I thought it might, but I think it will be enough. It did not seem to be running very fast, but a check with my hand-held tacho indicated 3100 rpm.

Further work on the control system is covered in the Electrics section.