Valve Clearance Check

Part of the periodic maintenance on the KTM is to make sure that there's the appropriate clearance between the cam and the followers when the valves are fully closed. Too much clearance means that the valves are not opening the whole way and causes extra noise and wear from the drive train. Too little clearance means that the valves are not seating fully and can make the bike hard to start or cause burned valves because much of the heat is transferred to the head through the seat when the valve is closed.

As an engine wears over time, the valve clearance generally decreases as the hardened steel valve seats are very slowly pushed further into the aluminum head by the hammering of the valve. In this bike, there are small steel shims that fit in the cam follower to allow some adjustment. If the clearance is less than the appropriate amount, the shim is replaced with a slightly thinner (like by 0.0015") shim so that the cam-to-follower clearance is corrected.

The specifications for this motor call for 0.003-0.005" clearance for the intake valves and 0.005-0.007" clearance for the exhaust valves—this is measured when the engine is cold. The clearance for the exhaust valves is usually specified to be more than the intake valves because they will get hotter and expand more than the intake valves.

inside the RF4 head

Although space is a bit tight, checking the valve clearance in an RF4 motor is really straightforward.

  1. Remove the fuel tank to get easy access to the top of the engine.
  2. Clean the top of the engine so you don't accidentally get any dirt inside the head.
  3. Pull out the spark plug lead.
  4. Remove the three bolts holding down the valve cover.
  5. Carefully remove the valve cover. The gasket is rubber and can be re-used if you do not damage it.
  6. Rotate the engine so that it is TDC in the compression stroke. There are many ways to do this.
  7. Measure the clearance between the cam and follower using feeler gauges.

If you have to swap shims to adjust the clearance, you need to remove the cams and it gets a little bit more finicky. Fortunately, all of the valves on the bike were in spec, so I just buttoned it back up. I'm a little surprised that everything was in spec—I think it means I just need to ride the bike harder!

It was nice to do some maintenance that didn't actually require any expense other than my time.