How to Adjust the Valves in a Yamaha 650by Floyd Drake IIIUpdated November 07, 2017
Items you will need
3/8-inch drive socket wrench
Metric socket set
Metric wrench set
Small metric crescent wrenches (optional)
Originally called the XS1 when introduced to North America in 1970, the Yamaha XS650 was a Japanese copy of British parallel twin-cylinder motorcycles such as the Triumph Bonneville and BSA Lightning. Known for reliability and ease of maintenance, the XS650 lacked some of the style of its British counterparts but made up for it in performance. To properly adjust the valves on the XS650, the cam chain must be adjusted prior to the valves. The XS650 valves can be adjusted on a cold engine, which eliminates the danger and difficulty of working on a hot engine.
Remove both spark plugs with a socket wrench and spark plug socket. Shift the transmission into first gear. Place the motorcycle on its center stand.
Use a wrench (preferably a crescent wrench) to remove the cap located behind the cylinders, underneath the carburetors. Inside the hole is a threaded stud with a lock nut on the end. Inside the stud is a small pin, which should be even with the end of the stud. If it is not flush, it needs to be adjusted.
Rotate the rear wheel forward. While rotating the tire, the pin should move in and out an equal distance in both directions. Stop turning the tire when the pin is in the middle of its stroke. Loosen the lock nut with a wrench and turn the stud until the end is even with the end of the pin. Tighten the lock nut and replace the cap. The cam chain is now adjusted.
Look into one of the spark plug holes using a flashlight. Turn the rear wheel until the top of the piston is visible in the spark plug hole. The engine is now at top dead center.
Remove the valve covers using a crescent wrench. Four valve covers are located on the front and back of the two cylinders; three are round and the left front cover is square. The exhaust valves are at the front of the cylinder and the intake valves are at the back.
Adjust the valves on the cylinder at the top of its compression stroke, which is the one with the closed exhaust valve. Insert a feeler gauge of the correct thickness between the rocker-arm bolt and the top of the valve stem. The clearance is correct when the next size up feeler gauge will not fit in between. Adjust using a crescent wrench by turning the bolt on the top of the rocker arm counterclockwise to tighten or clockwise to loosen. Bring the other cylinder to the top of its compression stroke and repeat. Remount the four valve covers.
According to 650 Central, the valve clearance specifications for the Yamaha XS650 are: 1970 to 1972 models, intake valve .003, exhaust .006; 1973 to 1975 models, intake .003, exhaust .004; 1976 and 1977, intake .002, exhaust .006; 1978 models, intake .004, exhaust .006; and 1979 to 1983 models, intake .0024, exhaust .006. Measurements are in thousandths of an inch.
A native of New Haven, Conn., Floyd Drake III began writing in 1984. His work has appeared in the "New Haven Register," Medford's "Mail-Tribune" and the "Ashland Daily Tidings." Drake studied journalism at Southern Connecticut State University. After working as a reporter in Oregon, he is now based back home in New Haven.