Introduction
13
Valve lash
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 mower for easy access to the cylinder
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 1.12.
4. 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 used not to damage the valve cover gas-
ket, it can be re-used.
5. Confirm that the piston is at T
op-Dead-Center on the
compression stroke. See Figure 1.13.
• 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 1.12
Spark plug hole
High tension lead
(plug removed)
Valve cover
Figure 1.13
Valves closed
(push rods slack)
Probe to confirm piston
is at top of travel
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