Mechanic: Shawn Ulikowski
Text: Dan Worley
Has the old thumper been a little hard to start lately? Do you get more of a workout trying to ignite your bike than you do riding it? If you answered yes to these questions, old Betsy needs a few minutes of your time to get her running smoothly again.
Despite all the benefits of four-strokes (top ends last forever and you really can “fill up” at the gas pumps), there are times they may be a little more work. The more moving parts a motor has, the more things wear out, which means more maintenance if you want to keep all of your ponies in order.
Valves are one of the most abused parts of the entire motor; they basically have a hammer slamming into them constantly just before they turn around and have a spring pound them back into the head. Doesn't sound like much fun, but most new four-stroke bikes have titanium valves that can endure a ton of slam dancing.
Shawn Ulikowski came by the shop to explain that it is a good idea to check valve clearance after the first couple of rides on a new bike, and then once per year is sufficient for most average riders. After a new bike has been broken in, the valve clearance can change. As parts settle or seat, many parts will have slightly larger tolerances. In the past, this was a huge issue, but the modern bikes of today are much better.
Though it sounds a little intimidating, it's actually easy to check valve clearance. The bad news is that if the clearance is not up to spec, it will require a little more work. We won't get into that part today, as it's a little complicated for such a short feature, but your owner's manual will guide you through the steps in an easy fashion. Checking valve clearance is fairly universal for all the brands, so follow these steps and get your baby back to good health.
Step 1) It is always wise to start with a clean bike since internal engine parts will be exposed. Try to get the top of the engine and the area under the gas tank as clean as possible. Remove your seat and gas tank to expose the valve cover on top of the motor.
Step 2) Use compressed air to blow out the spark plug hole before removing the spark plug cap, then remove the valve cover. On the Honda CRF250R there are two 10mm bolts to remove the cover.
Step 3) Now that the head is off, it is time to find top dead center (TDC). On the CRF250R the easiest way is to use the kickstart lever to turn the motor over slowly. Once you hear the decompression lever “click,” you have found TDC. The cam gear will have two flat marks that will line up with the top of the head. Every brand will use different marks on the cam gears to locate TDC. Please use you owner's manual to refer to the proper technique for finding TDC. If you try to measure the valve clearance at any other location, the measurements will be off and there is a chance of making a costly mistake.
Step 4) First check the intake valves (the two or three valves closest to the carburetor). Using a feeler gauge, slide the appropriate petal between the cam and the valve. Do not force the petal in; The fit should be nice and snug. Refer to your owner's manual for the proper tolerances. On the CRF the clearance should be between .004 to .006 thousandths of an inch or .09 to .15 hundredths of a millimeter. If your ride doesn't fit these standards, the cam will have to be removed and a different sized shim must be installed.
Step 5) Using the same method, check the two exhaust valves. All the brands except the Hondas will have a cam above the exhaust valves and look similar to the intake side. Hondas only have one cam so they need a rocker to open the exhaust valves, but the feeler gauge is still placed between the valve buckets and the rocker arm.
The CRF clearance specs for the exhaust are .010 to .012 thousandths of an inch or .25 to .31 hundredths of a miillimeter.
Step 6) Now that it is confirmed that the valve clearance is up to par, the valve cover, spark plug cap, tank, and seat can be installed back onto the bike and you're ready to ride!