The basics of checking your valves
Adjustment is unnecessary on motorcycles equipped with hydraulic lash adjusters (hydraulic tappets). However, the appropriate clearance is needed between both the intake and exhaust valves and the valve opening/closing mechanisms in all other 4-cycle engines. This clearance allows for a change in the size of the valve caused by thermal expansion as the heat of the combustion chamber is transmitted to the valve.
If there is too much clearance, it may result in engine noise (tappet noise). If there is too little clearance, the valve is pushed during the heated period, causing a drop in compression, resulting in bad idling and, eventually, burned valves.
Adjust the valves using the appropriate service manual procedures. (And if you don’t have one, which is why you are here, a Haynes or Clymer manual for your bike, or importantly, something similar made provide adequate guidance. There are also online videos, or riding buddies with more wrenching experience. Take your time, and be willing to sleep on an issue that is unclear. Have a plan before you start.)
Inspect and adjust the valve clearance when the engine is cool (under 35°C/95°F}.
Inspection and adjustment of valve clearance should be performed with the piston at top dead center of the compression stroke. This position can be obtained by confirming that there is slack in the rocker arm when the stamped “T” mark on the flywheel rotor and the index mark on the crankcase cover are aligned. If there is no slack in the rocker arm, even when the T-mark and index mark are aligned, it is because the piston is moving through the exhaust stroke to top dead center. Turn the crankshaft one full rotation and match up the T-mark again. The piston will then be at the top of the compression stroke (top dead center).
On in-line 4-cylinder engines with the firing order 1-2-4-3, the inspection of valve clearance can be conducted by rotating the crankshaft twice. After the above procedure has been property carried out, the inspection and adjustment of all cylinders is complete.
(In-line 4-cylinder engines are numbered 1-2-3-4 starting from the left cylinder.)
On V-twin and V-4 engines, inspection and adjustment are performed by placing each cylinder in the compression, top dead center position.
The valve clearance adjustment is correct when the specified feeler gauge fits snugly, but the next size larger feeler gauge will nol tit in.
On motorcycles that have a decompression mechanism which lifts the valve when starting the engine, the adjustment for decompression must be carried out first in order to provide an accurate valve clearance inspection.
Valve clearance inspection on engines with common, screw-type adjusters is measured by inserting a feeler gauge directly between the end of valve stem and the adjusting screw.
On one-sided ball-joint type engines, the clearance is measured by inserting the feeler gauge between the rocker arm and the cam.
For valve lifters in direct push-type engines, the clearance between the cam lobe and lifter or shim is measured with a feeler gauge.
If adjustment is needed. loosen the lock nut and the adjusting screw and insert the feeler gauge. Proper intake and exhaust valve tolerances are found in model specific manual(some specs may be found elsewhere on this site).
Turn the adjusting screw until the inserted adjustment gauge can only be pulled out with a little difficulty.
Leaving the feeler gauge inserted, and being careful not to turn the adjusting screw, tighten the lock nut to the specified torque.
An improperly tightened lock nut can loosen, and obviously cause serious engine damage.
When the lock nut is tightened, the clearance may change. So be sure to recheck the clearance after tightening the lock nut.
Adjustment is properly carried out only when the feeler gauge can be pulled out with a little difficulty. If tension on feeler gauge is too great or too little, readjust.
For valve lifters in direct-push-type engines, change
the shim to adjust the valve clearance. Refer to the
Model Specific manual for the appropriate adjustment method.