Setting the valves on an XS650
Step One: ADJUST THE CAM CHAIN.
(1) First provide ability to turn the motor:
Put the bike on the centre-stand, remove both spark plugs, and put it in top gear. This is so you will be able to rotate the engine by turning the wheel with your hand. Or alternatively put the bike in neutral, remove the alternator cover on the left side of the engine; that is the plate held on by two Phillips head screws with the word "Yamaha" on it, and then you can rotate the engine using a socket wrench on the nut in the centre of the alternator rotor. ALWAYS ROTATE THEY ENGINE IN AN ANTI-CLOCKWISE DIRECTION, LOOKING FROM THE LEFT, OR BY TURNING THE WHEEL FORWARD. If you rotate the engine backwards your settings will be off.
(2) Access the adjustment:
Remove the big cap screwed onto the back of the cylinders just below the carburetors. A big crescent wrench is suitable for.
(3) Check the adjustment:
There is a large threaded stud underneath the cap, with a hole down it's centre. This stud has a hex on the end, and a large lock nut. There is a pin visible in the hole, which should be flush with the end of the stud. However, if the adjustment is off, the pin will be either protruding or recessed. If it is flush, then rotate the, looking at the pin. It should just move a little, in and out, as you rotate the engine. It should come out as much as it goes in.
(4) Adjust if necessary:
Loosen the big locknut. Then turn the threaded stud either in or out as necessary so it ends up with its end just flush with the pin inside the hole in the centre of this stud.
(5) Check the adjustment:
Then rotate the engine, looking at the pin. Again, it should just move a little, in and out, as you rotate the engine. It should come out as much as it goes in. If not right, turn the stud a little more.
(6) Button it up:
When correct, tighten the locknut and replace the cap; the cam chain is now correctly adjusted.
Step two: SET THE VALVES
In addition to the normal 12mm and 10mm ring wrenches, you will need a small crescent wrench and a set of feeler gauges.
(1) Make sure the engine is cold, or the settings will be wrong:
The engine must be completely cold and not have run at all for a number of hours.
(2) Get the engine to TDC (Top Dead Centre):
With the bike still on the centre stand, shine a flashlight into either sparkplug hole. Rotate the engine slowly. Watch the top of the piston through the spark plug hole. When it is at the top of it's stroke, stop rotating the engine. You can also use a screwdriver blade or a wooden dowel to "feel" the position of the piston, just be careful not to jam anything, or drop anything into the cylinder. A flashlight is safer.
(3) Remove the valve covers:
These are the (4) covers at the top of the engine front and back. Three are round with three bolts each, one in the left front is square with four bolts.
(4) Determine which cylinder has come up on the COMPRESSION stroke:
Do this by looking at the valve rockers. The cylinder that is NOT at the top of the COMPRESSION stroke will be at the top of the EXHAUST stroke, and the exhaust (front) valve will be depressed by the rocker. On the cylinder at the top of the COMPRESSION stroke you should be able to feel a slight ability to rock both the rockers, but this is not always the case. The movement is very small.
(5) Check the valve clearance on the cylinder that has come up on the COMPRESSION stroke:
Use the feeler gauge to check the clearance, referring to the settings listed below for the various model XS650’s. This is the clearance between the bottom of the square headed screw that goes through the rocker, and the top of the valve stem, which is peeking above the spring. You choose the feeler gauge with the number etched on it per the settings given below, and try to slide it in between the bottom of the screw and the top of the valve stem. The gauge must just be able to slide in, with a slight feel of drag. The best way is the go/no-go method, i.e. the correct gauge will slip in, but the next largest size will not. The inlet valves are the valves at the back of the cylinder, the exhaust valves are the valves in the front of the cylinder;
The settings are:
Inlet .003 (three thou.)
Exhaust .006" (six thou.)
Inlet .002 (two thou.)
Exhaust .004" (four thou.)
Inlet .002 (two thou.)
Exhaust .006" (six thou.)
Inlet .004 (four thou.)
Exhaust .006" (six thou.)
Inlet .0024 (two and a half thou.)
Exhaust .006" (six thou.)
(6) Set the valves:
Set the valves on the cylinder on the COMPRESSION stroke. Put the wring wrench on the locknut on top of the valve, and turn it anti-clockwise. It will be tight. Turn it about one quarter turn, and keep the wrench on it. Then, using the crescent wrench turn the square headed screw either in or out depending whether you need more or less clearance. We are talking about fractions of a turn here. Then lightly lock the locknut, holding the square headed screw with the crescent wrench so it doesn't move, and check the clearance. Repeat until it's exactly right. When it's exactly right, tighten the locknut. Recheck.
(7) Rotate the engine one revolution exactly:
Shine the flashlight into either sparkplug hole and rotate the engine slowly so that the piston goes down once and comes back up. Stop when it's at Top Dead Centre.
(8) Now do the other cylinder:
Check the gap and set if necessary the other cylinder's valves
Repeat steps (5) and (6) for the other cylinder.
(9) Button it up:
Replace the valve adjustment covers, making sure to keep the gaskets or o-rings in place, the bike will have one or the other.
That's all there is to it!
Farrell