B3.9 and B5.9 Series Engines
Air Compressor Unloader and Valve Assembly (012-013)
Section 12 - Compressed Air System - Group 12
The unloader body is installed with spring tension. Use
care when removing to prevent personal injury. Always
wear protective eyewear.
Holset QE Models
Hold the unloader valve body down, and remove the four
Remove the unloader valve spring.
Remove the unloader valve cap.
Remove the unloader body gasket and unloader valve cap
rectangular ring seal.
Do not use caustic cleaners. Failure to do so can cause
Remove all carbon and varnish from the unloader valve cap
Inspect for Reuse (012-013-007)
Valve Spring Tester, Part No. 3375182
Use the valve spring tester, Part No. 3375182, to check the
Replace the unloader spring if it does not meet the speci-
fications shown, or the wrong spring has been used.
both cylinder and center unloader springs. Holset recom-
mends that new springs be installed during rebuild.