Engine
7
Valve lash
NOTE: Valve lash is the clearance between the top of the
valve stem and the rocker arm. The valve lash
should be checked after the first 25 hours of use
and every 100 hours after that. Valve lash can be
checked and adjusted using the following steps:
1. If the engine has been run, allow it to cool thoroughly.
Position the equipment for easy access to the cylin
-
der head.
2. Disconnect the high-tension lead from the spark plug
and ground it well away from the spark plug hole.
3. Remove the spark plug using a 13/16” or 21mm
wrench. A flexible coupling or “wobbly” extension
may help.
See Figure 2.3.
4. Disconnect the breather hose from the valve cover.
See Figure 2.4.
5. Remove the four bolts that secure the valve cover
using a 10mm wrench, and remove the valve cover
from the engine.
NOTE: If care is taken not to damage the valve cover gas-
ket, it can be re-used.
6. Slowly pull the starter rope until air can be heard
coming out of the spark plug hole.
7. Confirm that the piston is at Top-Dead-Center on the
compression stroke.
See Figure 2.5.
• The compression stroke can be distinguished
from the overlap stroke by the presence of air
pressure at the spark plug hole and the fact that
neither of the valves should move significantly on
the compression stroke.
• There is an automatic compression release mech-
anism that “bumps” the exhaust valve as the piston
rises on the compression stroke. At TDC, the
exhaust valve should be fully closed.
Figure 2.3
Muffle
Valve cover
Spark plug
Figure 2.4
Breather hose
Figure 2.5
Probe to confirm piston
is at top of travel
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