Checking Valve Clearance

This simple examination can help your valves live a long and lash-free existence.

High-performance motorcycle engines require hardly any maintenance at all. Yep, you should keep the oil clean and change the filter, but often service recommendations suggest that inspecting the valve clearances is something done infrequently.

For example, on Yamaha's latest 20-valve literbikes, you're not expected to check valve clearances (sometimes called valve lash) at the initial service; Yamaha thinks you can forget about the valves until 26,600 miles!

We're going to tell you how to check valve clearances, but not how to actually make the adjustments. Why? In part, because there's not enough space in How-To to do the subject justice, but also because many modern engines must have their camshafts removed to gain access to the adjusting shims, which is a considerably more complicated mechanical endeavor.

These engines use what's called shim-under-bucket adjustment, in which small steel shims are placed between the end of the valve stem and the bucket follower that's in contact with the camshaft lobe. You must remove the cams to liberate the buckets to even see the shims. Other designs may use screw-and-locknut or shim-over-bucket adjustment; in either case, you can adjust the valve clearances without pulling the cams.

With some bikes, there are special tools that allow you to extract the above-the-bucket shims without removing the cams. On a cold bike, start removing bits and pieces until you have a clear shot at the valve cover. A shop manual and digital camera will help you keep track of what goes where. (1)

Be patient and consult that shop manual. If it says you'll need to remove the carbs, for example, you should do so; shortcuts seldom work out to your advantage. Be particularly careful to clean the area around and above the cam cover before you remove it; some bikes collect muck beneath the airbox or fuel tank, and you don't want this stuff in your engine.

Some bikes, like this Yamaha FZ1, require that you drain the radiator slightly before removing the upper coolant hoses. When you remove the cam cover, pay attention to the orientation of the O-ring and any other sealing devices under the mounting hardware (2).

Next, remove the cam and timing covers (3, 4). You will use the ignition trigger as a reference for the proper crank position for measuring valve clearances. Again, consult your manual. On the Yamaha, you start with the number-one cylinder. Set the T on the ignition rotor to the crankcase split line behind the pickup. This sets top-dead center on the number-one cylinder. Use a wrench to turn the crank.

Now look at number one's cam lobes; they should be pointing away from each other (5). If they're not , you've got the engine at TDC on the exhaust stroke; rotate the crank one full turn. Reference your manual for the proper cold clearances. For the Yamaha it's 0.11mm-0.20mm on the intakes and 0.21mm-0.25mm on the exhausts. Hint: You can find this information on the "smog" tag on the frame (6).

Grab your feeler gauges and pick out the one matching the desired cold clearance. Gently slip the feeler gauge in between the cam lobe and follower of the number-one cylinder's valves (7).

It should slip smoothly between the surfaces. So far so good? Try the next-thickest gauge. Does it fit? Continue until you find the thickest gauge that will go in without jamming or binding--this one's too thick (8).

If the gap is too small, work down to the gauge that does fit. That's your cold clearance. Write it down in your service manual before you forget it. Continue with the other valves on this cylinder and then move to the number-two cylinder after you've rotated the crank 180 degrees clockwise. Check, rinse, repeat.For the number-four cylinder, rotate the crank another 360 degrees clockwise and check; for the number three, rotate the crank another 540 degrees clockwise. Don't get confused; all you're doing is ensuring that the cam lobes are facing away from each other on the cylinder you're measuring. It's that simple.

What if you find out-of-spec clearances? Borderline loose clearances aren't worth worrying about immediately, but tight valves should be adjusted as soon as possible.

Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!

*Please enter your username

*Please enter your password

*Please enter your comments
Comments:
Not Registered?Signup Here
(1024 character limit)
Motorcyclist
  • Motorcyclist Online