78/83/90 Series Horizontal Shaft Engines
12
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 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
mechanism that “bumps” the exhaust valve as
the piston rises on the compression stroke. At
TDC, the exhaust valve should be fully closed.
8. Check valve lash between each valve stem and
rocker arm using a feeler gauge.
9. Intake valve lash (carburetor side) should be 0.004”-
0.006” (0.10 - 0.15mm).
See Figure 1.14.
10. Exhaust valve lash (muffler side) should be 0.006-
0.008” (0.15 - 0.20mm).
See Figure 1.15.
11. Use a 10mm wrench to loosen the jam nut, and a
14mm wrench to adjust the rocker arm fulcrum nut.
See Figure 1.15.
• Tighten the rocker arm fulcrum nut to close-up
the clearance between the end of the valve
stem and the contact point on the rocker arm.
• Loosen the rocker arm fulcrum nut to open-up
the clearance between the end of the valve
stem and the contact point on the rocker arm.
12. Hold the fulcrum nut with a 14mm wrench, tighten
the jam nut to a torque of 80 - 106 in-lb. (9-12 Nm)
using a 10mm wrench.
Figure 1.13
Valves closed
(push rods slack)
Probe to confirm piston
is at top of travel
Push rods
relaxed
Figure 1.14
.006” feeler
gauge
Figure 1.15
.008” feeler
gauge
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