MTD Engine - Series 350/450/650
6
5.12. Fuel: Use clean, fresh fuel with a pump octane
rating of 87 or greater.
• Stale or out-of-date fuel is the leading cause of
hard starting issues.
• Pump octane ratings beyond 87 will not improve
engine performance.
• The gasoline can have a maximum of 10% etha-
nol or 15% MTBE.
• Do not use E85 in MTD engines.
5.13. Valve lash can be checked and adjusted using
the following steps:
5.14. If the engine has been run, allow it to cool thor-
oughly. Position the mower for easy access to
the cylinder head.
5.15. Disconnect the high-tension lead from the spark
plug and ground it well away from the spark plug
hole.
5.16. Remove the spark plug using a 13/16” or 21mm
wrench. A flexible coupling or “wobbly” exten-
sion may help. See Figure 5.16.
5.17. 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.
5.18. Secure the safety bale with a spring clamp, and
slowly pull the starter rope until air can be heard
being expelled from the spark plug hole.
5.19. Confirm that the piston is at T
op-Dead-Center on
the compression stroke. See Figure 5.19.
• TDC can be identified using the probe. The key-
way in the PTO end of the crankshaft also corre-
sponds with the crank pin (and piston) position.
• 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.
5.20. Check valve lash between each valve stem and
rocker arm using a feeler gauge.
See Figure 5.20.
Figure 5.16
Spark plug hole
High tension lead Muffle
(plug removed)
a
ve cover
Figure 5.19
Valves closed
Probe to confirm piston
is at TDC
Figure 5.20
Setting exhaust valve lash
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