diameter than the exhaust valve, so it is heavier. Therefore, by increasing the number of intake valves, the inertial mass of the entire intake valve is reduced to reduce the valve drive output. The three intake valves are not aligned and the central valve is closer to the end. However, he said that all three extension lines of the valve stem pass through the center line of the camshaft, and all the valves are opened and closed directly by the camshaft. Racing history Yamaha was scheduled to participate only in the All Japan F2 Championship at the time of the announcement but changed its policy to participate in the Fuji Grand Champion Race (Fuji GC) as well. Since commercialization is a prerequisite for participating in the GC, it was necessary to commercialize it from 1986. In the GC, the installation of a muffler is required by the rule, so its development was necessary. Regarding the muffler, it became necessary to even in F2 from 1985. The muffler was installed at the outlet of the exhaust pipe for each bank. The actual race participation was limited supply in 1985 for engine development, and from 1986 it was supplied in the form of the rental to those who wished. 1985 In 1985, a limited supply of Geoff Lees (F2/GC all rounds) and Keiji Matsumoto (from F2 Round 3) was implemented. In F2, Reese is up to third in the March 85J, sixth in the championship, and Matsumoto is up to second. At the GC, Reese was ranked fifth in the MCS-VI / March 842 and seventh in the championship, and was judged to have the same performance as Honda, so it was commercialized in 1986. 1986 In the 1986 series, Yamaha leased the supply of OX66 to the team and carried out maintenance with a designated tuner. Used by 9 people in GC/11 people in F2. As the number of users increases, maintenance cannot be done with Matsuura RS alone, so Tomei Engine and Ogawa Motor are also in charge of maintenance. Geoff Lees won the second round of the GC, Keiji Matsumoto won the third round of the GC, and finally, Reese became the champion. In F2, he won a total of four races, but he couldn't win the championship. However, it was found that the overhaul cost of OX66 would be two to three times that of the conventional BMW,