My first motorbike experience was a bike we built as mates when we were just turning 10. Lived near the Newcastle tip. Treasure land. Victa 18 came from there. A couple of inches of Rubber air hose forced over the end of the crankshaft, with washer and nut put back on to hold it there which ran directly onto the rear tyre of the 28" inch Speedwell. Bolted on via two 1/4" flat bars bent to 90deg angles. One engine bracket, bolted/clamped to the area that a side stand normally would be just in front of rear wheel but behind pedals crank. The other bracket bolted through lower frame spar that runs to rear. Pedal crank removed and a long industrial bolt with pipe sleeves fitted for foot rests pegs. Victa 18 fuel tank tied under top bar. Continuous direct drive. Throttle lever on handle bar. The smaller one of us would sit in the turned up racing bars. The skipper on the seat with thumb on throttle. A third would push until fired!! Then run along beside and jump up side saddle on to the top bar. Obviously we only rode it on the road. It was fast too. We loved it. Coppers didn't, hence the forced closure of Newcastle Motorcycle inc.
It was shortly after that we discovered stepthru's, had a thing called suspension. So we disappeared into the scrub in stead.
