ATV Tech: Illogic in the World of Valves

Sometimes logic has no place in the rough and tumble conditions of a modern ATV engine operating at full tilt. Logic would suggest that as your engine’s valves open and close millions of times, they would slacken up, become loose and sloppy. However, the truth of the matter is that often valve clearances actually become tighter over time.

And unlike say, your axle nut, a valve that has gotten tighter on you is not a good thing. How can you tell right away that you may have valve clearance issues without doing the right thing and breaking out your feeler gauge? Hot starting will become difficult. Your ATV will turn over but be reluctant to fire up when it’s been running. The reason for this is that heat naturally expands metal- valves out of tolerance will become lifted off their seats because of this expansion, allowing crucial engine compression to escape.

A dip in compression will be most noticeable as difficulty in starting but you will be experiencing decreases in power output as well. Sometimes this deficit is quite obvious, other times not so much.

As valve clearances continue to drop, other maladies begin to present themselves. If, for example, even a single valve were to have no clearance, cold starting would become impossible as well. Go long enough with too little clearance and valves and seats will eventually be destroyed as a valve that can’t rest properly upon its seat cannot adequately disperse the heat of engine operation.

Here is the good news- checking your valve clearance isn’t rocket science. Your machine’s manual should provide you a range of proper clearance tolerances (and there’s always the Internet for those of you who lost your manual). Checking your tolerance is as simple as removing the valve cover and turning the engine until the cam lobe points away from the rocker arm (or valve lifter). Grab a feeler gauge and do some feeling. Make adjustments accordingly if your valves fall outside the range listed.