An update on the chronology of the old ST engines:
From the Dec 1968 World Engines advertisement in AAM, The G21/29 and G21/35 were changed to a single ringed piston.
* The plain bearing 35 (combat?) remained the same.
* The plain bearing 35 stunt was changed to a single ring.
* The G15 was new and came in both front and rear induction as a glow or diesel. Also, ST produced a conversion kit to switch from front induction to rear induction.

I also noticed that the G20/15 diesel shown had the longer intake. Mine (1960) has the short intake. Don’t know when they switched.

The G20/15 crankcase was updated in 1970, but I THINK by that time they only used it on the G20/15 glow and the G20/23 glow.

These changes may have been made a little earlier. I just happened to be reading that old magazine.

George

Edit: Oops, the mag was American Aircraft Modeler (AAM), not MAN.