Here's some info ........
In 1930, the Marconi Company asked the Norman company for a lightweight,
air-cooled petrol engine capable of driving a one-kilowatt generator. The
three prototypes were of 250cc, but by then the requirement had risen to
1.25 kilowatt, so the capacity was raised to 300cc. Production commenced in
1932 and continued in one guise or another until the factory closed down in
1968, the Mk2 being introduced at the end of the war. Certain features were
modified in an attempt to keep the price down. The oil filler is different,
the Mk 1 has a detachable starting handle and the bottom of crankcase is
finned, but the most noticeable difference is that the top of the main
casting behind the mag is rounded whereas the Mk2 has a flat top with tapped
holes for attaching a fuel tank. The flywheel doubles as a very efficient
fan and is cast in aluminium. Mk1 flywheels bolted to a steel hub but Mk2
are fitted direct onto the mainshaft.
The exhaust pipes curving around the engine leading to a common silencer are
the the alternative to the canister type silencers that fitted directly onto
the exhaust ports. The latter were optional from about 1948/9. Some engines
were also available with a paraffin conversion.
As a stationary engine, the Mk 2 was largely used on battery chargers and
lighting sets and, from 1938, large numbers were bought by the War
Department. The Admiralty bought them for use in charging sets on MTBs and a
marine version was also made, basically the same but without the governor.
Some were supplied to Imperial Airways for use on flying boats as Auxiliary
Power Units (APU's) and typical tasks would have been charging batteries,
bilge pumping and fuel lifting. They were also supplied to various firms for
driving compressors and Auto Diesels purchased large numbers of T300's to
power lighting sets.
The serial number on these engines is found on the left side of the
crankcase and is repeated on the brass plate on the top of the governor.
That said, many of the WW2 engines do not have a serial number and in any
case, the numbers frequently do not agree as parts are readily swapped from
one Mark to another and most parts are interchangeable. About 5,000 MK 1's
were made and around 7,500 Mk 2's. Confusingly, Mk1's have serial number
commencing with TE whereas MK2's begin TA. For Mk2's, the post war numbers
ran:- 1945 TA1001, 1950 TA4673, 1960 TA8034, 1968 TA8590.
From a practical point of view, the engines are very light to carry about,
easily started and are smooth in operation, but Mk1's are said to be
noticeably smoother than the later engines.
If you want to know more about these interesting little engines, Stationary
Engine magazine published a comprehensive article by Phillip Gallimore in
numbers 95, 96, 98 & 100.