Recently, you may have heard that new and more strict EPA emission standards have phased out the production of those good old 2-stroke dirt bikes that many of us had in our youth. Now they are being replaced with cleaner-operating 4-stroke models. We asked MMI Instructor, Chris Reo, what that change would mean to dirt bike riders. Chris told us that one major difference would require the owners to pay more attention to valve adjustments. He then proceeded to tell us just how to deal with this issue.

To begin, Chris says that the valve clearance needs to be adjusted, or the space between the cam and the valve bucket at top dead center. Adjustment is important because too much space can cause the valves to make an annoying clicking noise and will rob the engine of horsepower. On the other hand, if there is too little space, the valves may overheat or become stuck. Getting the precise measurement or clearance is really important. However, before you begin this procedure, Chris suggests that you have four items handy: (1) The correct manual for your bike, which tells what the proper valve clearance should be (as well as other necessary factory specs) (2) A clipboard, pen, and paper to write down measurements and notes (3) A set of proper tools for disassembly and assembly (4) A feeler gauge for measuring the clearance.

While the process of making these adjustments is not extremely difficult for those who do a lot of wrenching, it still can be a bit overwhelming the first time through. There are lots of steps to remember. As with most engines, parts are not always interchangeable. You'll need to be aware of and make notes about the location of certain C-rings. You'll also need to remember which one is the intake cam and how to tell the difference between it and the exhaust cam. Another handy piece of advice is that after removing the cams, don't let that cam chain fall down into the engine! Just use a screwdriver to run it through the chain, and place the screwdriver crossways on top of the engine (see Chris perform this step in the video). You'll also need to measure and replace the shims that control the valve clearance. After you put everything back together (including a gasket replacement), you'll need to torque the engine to factory specs (also found in your owner's manual).

This summary has touched on only a few of the steps that are required to perform this task. Please be sure to review the video segment of this episode to see Chris perform all the measurements and adjustments as he leads you through the step-by-step process. In addition, Chris says that if you are a bit overwhelmed or unsure of what you are doing, you should play it safe and take the bike to your dealership where a certified mechanic can do the work.

Back to Episode CRN10006