Tech Tips

Valve Adjustments 101

Written by  May 31, 2004

After doing the last article on Nitrous Oxide Systems (NOS), I decided to come back to Earth and get down and dirty on tech advice. Most people wonder why the valve adjustment procedure must be done.

Engines that are new will break-in; this causes part clearances to change. After metal gets warm due to heat and friction, the tolerances will change as well. When the engine breaks in, the Valve Seat area will wear, this will cause the valve clearance to be out of specified value. All 4-cycle motorcycle manufacturers recommend this service be performed by their standards. There are several valve adjustment types in service today, they are as follows:

Rocker screw type
Shim Over and Under (requires Camshaft removal)
Hydraulic Lifter with pushrod (Most Harley EVO Engines)
Solid lifter with pushrod (V Motor Race application)
Eccentric Type


When the valves are out of adjustment, this will cause premature engine wear and decreased performance. Engine idle will also be affected. You may notice that you hear a tapping sound from the top end of the engine when hot; this is normally caused by valve clearance being too loose. When the engine has a lot of miles on it and you do not hear any noise from the valve train area, most likely the valves are on the tight side. By adjusting valve clearance you will gain better running conditions and power. By having the valves serviced on a routine maintenance schedule, you will gain long engine life and maintain the performance that you desire. If you do not have the valves of your motorcycle serviced, you will eventually wear out the valves, Camshaft and other expensive top end components. If you are not comfortable with this procedure, and you do not have the appropriate tools, I recommend that you DO NOT try this procedure. Please consult your local certified motorcycle technician to have this procedure performed. They have extensive factory training on the latest models that are in production today.


By Dave Miller