Hi Erin
You'll have to wait for photos, but here's a more detailed description:-
The engine is built using technics components entirely sourced from kit
8462.(Pneumatic recovery truck)
A wheel is mounted centrally in a frame( to act as a flywheel) then outside of
the wheel bearings on each side is a crank to which is connected a pneumatic
cylinder. A further frame then supports the outside of each crank, then outside
that on each side is a cam. The cranks are offset by 90 degrees relative to each
side. The cam on each side trails its crank by 90 degrees. Each cam acts on an
arm both above and below it which is connected to an air change-over switch. The
upper and lower arms are linked. Thus, as the cam turns, it moves the arm and
changes the airflow, via the switch, from one end of the cylinder to the other
at the appropriate time. 2 pressure tanks and a pressure pump are also mounted
on the frame. After about 30 pumps, the whole contraption wheezes into life and
continues to turn slowly over as long as the pump is pumped.
Future improvements are :- a) a more rigid crank - the effort of turning the
cams tends to make it flex! b) a heavier flywheel and c) trying to eliminate
friction from the 2 air switches, which are rather stiff in operation.

Hope this makes sense...cheers...John ...(aged over 18 - lots over 18!!).