Cub Cadet MTD P90 Series - Manual (Page 18)

P90 Series Vertical Shaft Engines
12
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 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 1.10.
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 gasket, it can be re-used.
5. Confirm that the piston is at Top-Dead-Center on
the compression stroke. See Figure 1.11.
• 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.
Figure 1.10
High tension lead
Muffler
Valve cover
Figure 1.11
Valves closed
(push rods slack)
Probe to confirm piston
is at top of travel