Symtoms of excessive valve clearance:

• Tapping, rattling sound coming from top of engine.
• Poor performance

Symtoms of too tight valve clearance:

• Poor compression, especially when engine is hot.
• Rough idle.
• Poor fuel economy.
• Burn/damaged valve/valve seat.

General notes:

• As the cam lobes and slipper faces wear the valve
  clearance will increase.
  
• As the valves and the valve seats wear the valve
  clearance will decrease.
  
• The valves are closed ¾ of the time and while closed
  are cooled by contact with the valve seat, the exhaust valve
  relies heavily on valve seat contact for cooling, thus if the
  valve does not close fully the valve will over heat and burn.
• Valve clearance should be near zero when the engine is at
  normal operating temperture, when the engine cools the valves
  will shrink due to thermal contraction thus causing a clearance
  to open up. The longer the valve stem the more clearance it
  will require. Exhaust valves get hotter than inlet valves so
  usually require more clearance.
• Valve clearance should be inspected on a cold engine.
• Valve clearance should be measured when the piston is at
  "Top Dead Center" on the compression stroke, turn crankshaft
  another 90° after the inlet valves close to reach this
  position, use the notch on the flywheel to find exact position.

Specific notes:

• Honda reccomend inspecting the valve clearances
  every 12,000 Km.
• Removing the rear rocker cover is easy, however,
  removing the the front rocker cover is difficult.
• You can tell the difference between the inlet
  and exhaust valves by the fact that there are two
  small inlet valves and one large exhaust valve.

Procedure

1. Ensure engine is cold.
2. Remove fuel tank and air box.
3. Disconnect all spark plug caps.



4. Rear cylinder.
   • Remove the timing hole cap and the crankshaft
     hole cap on the left side of the engine. Both
     caps require allen/hex keys to remove them.
   • Remove rear rocker cover.
   • Rotate the crank shaft counter clockwise while
     looking inside the timing hole until the "RT" mark
     aligns with the index notch on the crankcase cover,
     and make sure all the cam lobes are facing down and
     the piston is at Top Dead Center (TDC) on the compression
     stroke.
   
   
   
   • Inspect the valve clearances by inserting the
     appropriate blade of a feeler gauge between the
     contact points, if the clearance is correct you
     should feel a slight drag when you pull on the
     feeler gauge.
   • If the valves require adjusting then hold the
     square head of the stud with a special valve tool
     or with a pliers and loosen the lock nut with a
     tight fitting 10mm ring spanner. Adjust the
     clearance and re-inspect.
   
   
   
5. Front cylinder.
   • Remove radiator mounting bolts, but do not
     disasemble the cooling system..
   • Remove thermostat housing mounting bolt.
   • Remove the rocker cover by pulling it out
     the space left by the dropped radiator. Be
     carefull not to damage gasket surfaces.
   
   • Rotate crank shaft counter clockwise until
     the "FT" mark aligns wiht the index notch on
     the right crankcase cover, and make sure all
     the cam lobes are facing down and the piston is
     at Top Dead Center (TDC) on the compression stroke.
   • Repeat steps taken on rear cylinder.
   • Securely glueing the gasket into the rocker cover
     will making re-installation of the rocker cover easier.