 
The bike looked something like this when new except that it had the famous "Jampot" shocks and springs at the rear, so maybe the motor was an earlier model inserted in the sprung frame?
 engine                
single cylinder OHV 4-stroke
 cylinder bore
 piston stroke
 cubic capacity           
497cc
 bhp at rpm           
N/A (estimated 18 bhp)
 lubrication           
Dry sump
 carburetors           
One Amal Monobloc
 gears                 
4, right-hand foot change
 chassis               
Tubular steel
 tires
 weight
 max. speed           
N/A (estimated 113kph)
 brakes                
single leading shoe drums front and rear
Note
the heavy duty fork-brace and special Primary drive cover! Classic farm
engineering!
 Matchless
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