Stuart Turner WD

Had this one a few years, but still and interesting beast and a firm fav of mine.

In 1923, Stuart Turners and seven other companies were approached by the War Office to see if they could produce a light weight air cooled engine to drive a generator for military use. Five firms tried, but only the ST unit operated as it was supposed to & they got the contract. The brief was that the whole set should weigh no more than 84 lbs (38 kilos) as it was intended for forward radio positions in difficult terrain & would be carried on a pack mule. It must be unaffected by the position in which it was carried, be capable of operating in any temperature from freezing to 140oF and govern its speed to within 5%. There were other conditions too, but these are the salient details.

Originally, the engine was close-coupled to a 24-volt dynamo rated at 300 Watts. This unit was mounted on an aluminium base plate and protected by a lightweight steel tubular frame that was probably enclosed with a shaped canvas cover. The cylindrical petrol tank is fixed to the frame with leather straps before use. Few examples remain in any kind of complete state.

The engine is a lightweight, side valve, air- cooled, horizontally opposed twin. A single carburettor of typical ST design feeds the cylinders through nickel-plated bronze induction pipes. The crankcases are bolted to a sump that carries the oil supply. Both are in aluminium and have an all machined finish. A pumped oil supply is metered to 12 drops per minute & this is galleried through the engine to feed mains and big ends by gravity. The steel crankshaft supports slim connecting rods upon which operate cast iron pistons with three compression rings but no oil control ring. The cylinders and separate heads are of commendably thin section cast iron and are a tribute to ST's model making background.
According to its spec plate it turns out 1 BHP & the tight requirement of governed speed probably means it was used to directly drive radio equipment rather than just charge rather more forgiving batteries. It must have been pretty successful straight off the drawing board as surviving examples show few variations from early to late. 2 sets were used at Everest base camp and by government agencies.

Lovely - thanks for posting

Nice post Steve...
Worth chipping in that if anyone comes accross such an engine please get in touch with Steve and myself. I keep a register of these engines/sets and any new additions or changes to the register is useful to receive. I have one of these sets and the register has 27 engines/sets listed. There was a detailed article in the SEM issue 398 May 2007, and a follow up in issue 500 November 2015 which are worth a read. They are certainly something a bit different!
Cheers Dave