B3.9 and B5.9 Series Engines
A/C Cylinder Head (QE Models) (012-104)
Section 12 - Compressed Air System - Group 12
Inspect the upper part of the unloader valve cap where the
rectangular v-seal operates. Check for scoring.
Inspect the valve seat surfaces.
NOTE: Inspection of the valve seats in the valve plate
requires specialized equipment and is beyond the scope of
If the valve seat is visibly damaged, or can not be cleaned,
a new valve plate is available in a service kit. Otherwise, a
QE valve plate service assembly can be used.
Gasket sealing surfaces must be clean and free of all old
gasket material, carbon, rust, and other buildup. Surfaces
must be free of scratches, gouges, burrs, and other
After making sure all gasket surfaces are clean and free of
the above, inspect the head and cover for flatness. Use the
flat plate and the feeler gauges.