Made in 1947 and 1948 by the Air-O Supply Model Manufacturing Co. in Hawthorne, California, USA.
This engine is one of several short lived Post-War efforts by US manufacturers at marketing diesels to North American aero modellers. The perfection of the Arden ‘hot coil’ glow plug in 1948 effectively ended the possibility of diesel model engines gaining a serious toe-hold in that region. The US enthusiasts threw away their batteries, contacts and coils and wholeheartedly embraced glow ignition as the preferred model engine format.
It is an exceptionally well made engine. It features a hardened steel piston lapped and fitted in a mild steel cylinder. Cooling fins are machined integral with the cylinder promoting low distortion and effective heat dissipation.
Despite at first glance looking like a fixed compression engine, it does have a contra-piston. This is adjusted by a compression adjustment grub screw recessed on top for insertion of an allen key. Very neat.
Neither needle nor compression settings are critical and the engine is very easy to set.
Performance is steady though power output is gentle, as is to be expected on an engine of this vintage featuring piston port intake and single transfer port design.
Propeller fitted is a 12 x 6 Master Airscrew GF3. Maximum RPM is about 6,400.
Fuel mix is ‘jungle juice’; i.e. 3 equal parts of castor oil, di-ethyl ether and kerosene.
Further information on these rare engines may be found here:
https://www.modelenginenews.org/ad/aerod.html