Valve Lash - MTD 478 Series Professional Shop Manual

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 thor-
oughly. Position the equipment 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" exten-
sion may help. See Figure 1.8.
Spark plug socket
Muffler
Valve cover
Figure 1.8
4. Disconnect the breather hose from the valve
cover. See Figure 1.9.
Figure 1.9
5.
6.
7.
•
•
8.
Breather
hose
spring
clamp
7
INTRODUCTION
Remove the five bolts that secure the valve
cover using a 10mm wrench. Remove the valve
cover from the engine.
NOTE: If care is taken not to damage the valve
cover gasket, it can be re-used.
Slowly pull the starter rope until air can be heard
coming out of the spark plug hole.
Confirm that the piston is at Top-Dead-Center on
the compression stroke. See Figure 1.10.
Probe to confirm piston
is at top of travel
Valves closed
(push rods slack)
Figure 1.10
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
mechanism that "bumps" the exhaust valve as
the piston rises on the compression stroke. At
TDC, the exhaust valve should be fully closed.
Check valve lash between each valve stem and
rocker arm using a feeler gauge.