I sent an inquiry to tech@bonnevillespeedtrials.com 8 days ago and have received no reply. As such I have decided to ask my question here. As I read the chapter 5 rules regarding modified production frames the engine and frame of a motorcycle must be from the same manufacturer. Further limited production, off road and production road racers are legal if produced in numbers less than 500. No mention is made that the engine and frame be from the same model. I am planning to run a Yamaha 350 in the M-AG and M-CG classes. The frame is a raked 1971 R-5 350 street unit with 1971 R-5 cases. The engine is fitted with pre 1981 TZ-350 crank, pistons, cylinder, head, clutch, transmission, ignition system, carbs and pipes . The TZ-350 A & B was produced at approx 250 units per year As I see it the bike is legal for the classes mentioned. Am I correct? If not I'll just run it in the A-AG and A-CG classes.
I chose not to use the TZ chassis and cases because they are rare and valuable. Modifying the frame by raking it and damaging the cases in the event of engine failure will destroy the value of the components. The A & B model TZ-350 frame and the R-5 frame are identical in design the only differences being tubing thickness, bracketry and the TZ has a rectangular section swing arm. The TZ frame is 5lbs lighter than the R-5 frame. The cases are identical except for the front engine mounts and a triangular sheet metal bracket mounted by 3 screws behind the clutch. The TZ front mounts are bored to accept rubberized inserts added to prevent cracking of the frame from the engine being totally solidly mounted as in the R-5. The sheet metal bracket was added to prevent case spread due to the higher hp of the TZ. There is no performance advantage gained by using the R-5 items.
The swing arm I am using is a modified R-5 unit. The forks and triple tree are TZ-350 units. Wheels are RD-400 items. Rear brake is a TZ unit, seat is a modified Vesco TZ unit, tank is a Suzuki X-6 250 factory rr accessory.
