Yamaha YZR 500

From time I wanted to construct artisan a 500 cc 2 stroke engine for racing use and I spended 14 months of my free time to make real ideas... that I had in mind. I begun this "Opera Maxima" buying a 6 years old Cagiva Mito 125 cc motor-cycle without engine. The frame of this motor-cycle is exceptional and superabundant for road use: in fact it was only necessary to make few changes near at fork fulcrum to mount the bigger 500 cc 2 stroke Yamaha RD. Engine supports were reinforced because the bigger weight. [...] Yamaha engine was modified too. First of all I increased the compression ratio from 11.6-12.0:1 to 13.5:1 working faces of cylinder heads and using a lower head-cylinder gasket: so the squish is 0.9-1.0 mm. The four cylinders, fully jointed together crankcase, have the exhaust like the original, appropriately jointed together own valves, which ends in to exhaust mainfold with diameter of 36 mm instead of 33.0-33.5 mm. Cylinder inlets were completely changed: the 4th cylinder inlet, in front of exhaust, was enlarged in volume about 25-30 % more, in height and in lift 6-7° more. Side cylinder inlets were slightly enlarged in width increasing the washing phase of 5°.

Furthermore they were jointed together own engine cylinder, increasing lightly in volume too. I changed old Yamaha pistons (145,2 g) with four new lighter Vertex single-ring pistons (135,0 g). [...] After having studied several exhaust systems for two strokes engines, I planed four expansion exhaust heads of maximum diameter of 112 mm and shorter of originals of 10%. Two of four news are, seeing from up, straigth and pass under the tail, the others pass under the engine and come out from clutch under fork fultrum and have the initial piece slightly curved. For all exhaust new heads the initial diameter is 36 mm and divergence of first section after cylinder mainfold is greater than in the original exhaust heads. The expansion counter-cone convergence is increased of 3.0-3.5° too. The sheet steel is P04, bright, of 0,6 mm thickness, shears cutted, and shaped with hand calander. Air-acetylene weldings. [...] Marmdraw 5.0 created by LPSoft in VB6 code has permitted to develop on plane the surface of all cone and cylinder frusta in which was divided the exhaust heads and to print the development full-scale on A4 paper. It was simple to transfer trasferire the shape from paper to sheet steel. [...]