Holset Air Compressors Master Repair Manual – 012-104   Air Compressor Cylinder Head (Holset® QE Models)

If the cylinder head is removed while the air compressor is on the engine, drain the engine coolant. Reference the specific engine application manual.

Since the valve plate, head and unloader body are indexed, marking of these parts is recommended to make sure they are reassembled in the proper orientation.

WARNING  The unloader body is installed with spring tension. Use care when removing to prevent personal injury. Always wear protective eye wear.

Hold the unloader valve body down and remove the four capscrews.

Remove the unloader valve body.

Remove the unloader valve spring.

Remove the unloader valve cap.

Remove the unloader body gasket and unloader valve cap rectangular ring seal.

Remove the intake manifold and gasket.

Loosen, but do not remove, the center head capscrew.

Mark the head for orientation during assembly.

Loosen and remove the four corner head capscrews. Save and reuse the capscrews.

NOTE: If continuing with disassembly of the head, valve plate, and cover, make sure the work surface is clean. Debris pushed into the valve sealing surfaces by setting components on a dirty surface will cause a malfunction after assembly.

Remove the head, cover, and valve plate assembly and place it on a clean work surface with the intake valve facing upward.

Some units have a press-fit intake valve retainer. If present, carefully remove it to prevent part damage.

Remove the intake valve.

NOTE: The center capscrew is shorter than the four corner capscrews.

Turn the head assembly over and set it on a clean surface. Remove the center capscrew and the capscrew can be used again.

Remove the cover, cover gasket, head, and head gasket.

NOTE: The wave washers must be replaced.

Remove the two wave washers, exhaust valve retainer, and exhaust valve.

WARNING  When using solvents, acids, or alkaline materials for cleaning, follow the manufacturer’s recommendations for use. Wear goggles and protective clothing.

Soak the parts in a kerosene emulsion-based cleaner designed to remove carbon. The cleaner must have a pH of 9.5 or less to avoid turning aluminum parts black. The cleaner manufacturer or supplier can be contacted about solution concentration, temperature, and soak time.

NOTE: Do not use a scraper to remove carbon and scale, the sealing surfaces can be damaged.

The parts can be scrubbed with a stiff nonmetallic bristle brush.

Inspect the intake and exhaust valves for cracks or damage.

NOTE: Cummins Inc., recommends new valves be installed.

Measure the flatness of the intake and exhaust valves. Both valves must be flat within 0.03 mm [0.001-inch].

Replace valves if cracked, damaged, or not flat.

Inspect the upper part of the unloader valve cap where the rectangular V-seal operates. Check for scoring.

NOTE: Inspection of the valve seats in the valve plate requires specialized equipment and is beyond the scope of field service.

Inspect the valve seat surfaces.

If the valve seat is 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 deformities.

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.

Single cylinder heads must be flat within 0.03 mm [0.001-in] between any two adjacent capscrew holes.

Single cylinder top cover must be flat within 0.06 mm [0.0024-in] between any two adjacent capscrew holes and 0.10 mm [0.004-inch] total.

NOTE: Cummins Inc., recommends that new springs be installed.

Use valve spring tester, Part Number 3375182, or equivalent, to check the unloader valve spring. Replace any spring that does not meet specifications.

Reference the Compressor Spring Specifications chart in Section V.

Install the exhaust valve over the post in the valve plate.

Apply a thin coating of antiseize to the inside diameter of the exhaust valve retainer.

Slide the exhaust valve retainer over the valve plate. Make sure that the end of the retainer with the groove faces upward.

Align the wave spring gaps 180 degrees from each other not to overlap.

Place the wave springs in the retainer groove.

Determine the final orientation of the valve plate (air intake location) and the head (coolant ports with respect to air inlet or manifold location). Align the kidney-shaped slots in the head with the kidney shaped slots in the gasket.

If orientation marks were made before disassembly, use them.

Assemble the cover, cover gasket, head, head gasket, and valve plate.

NOTE: Make sure corner capscrew holes are aligned.

Lubricate the threads under the head.

Install the shorter capscrew with washer through the center hole.

Install the valve plate gasket.

Carefully place the intake valve in the valve plate. Install the intake valve retainer.

Install the valve plate assembly.

Lubricate the threads under the head and washer of the capscrews if initially installed.

Install the four head capscrews and washers.

Tighten all five capscrews.

NOTE: The seal must be installed with the grooved side up.

Install the new rectangular V-seal into the unloader body.

Liberally lubricate the unloader valve bore above and below the rectangular ring seal with high temperature Accrolube Lubrication Teflon grease, or equivalent.

Install a new o-ring seal on the unloader valve body.

Use clean 15W-40 oil or Accrolube Lubrication Teflon Grease, or equivalent, to lubricate the seal.

Liberally lubricate the unloader valve body bore and unloader cap with high temperature Accrolube Lubrication Teflon grease, or equivalent.

Install the unloader cap.

Install the unloader spring.

NOTE: The two unloader body screws must not be used to attach any brackets.

Lubricate the unloader screw threads and under head with clean engine oil (SAE 15W-40), before installation.

NOTE: The longer capscrews are used to mount the manifold to the air compressor.

Assemble the unloader components and attach the unloader assembly to the valve plate with the four capscrews and washers.

Install the exhaust valve over the post in the valve plate.

Apply a thin coating of antiseize to the inside diameter of the exhaust valve retainer.

Slide the exhaust valve retainer over the valve plate. Make sure that the end of the retainer with the groove faces upward.

Align the wave spring gaps 180 degrees from each other so they do not overlap.

Place the wave springs in the retainer groove.

Fabricate or reuse the four guide pin tools.

Insert the larger end of two guide pins in opposite corner holes of the valve plate.

Determine the final orientation of the valve plate (air intake location) and the head (coolant ports with respect to air inlet or manifold location). Align the kidney-shaped slots in the head with the kidney shaped slots in the gasket.

If orientation marks were made before disassembly, use them.

Install the head gasket onto the guide pins (either side up, but with correct slot orientation). Install the head onto the guide pins with the kidney-shaped slots aligned and toward the valve plate. Install the cover gasket over the guide pins.

Assemble the cover.

Install the shorter capscrew with washer, if initially installed, through the center hole.

Place the remaining two guide pins in the crankcase head capscrew holes (that will not interfere with the guide pins already in the head assembly). Install the valve plate gasket.

Carefully place the intake valve on the crankcase, located by the valve plate gasket. Do not allow the valve to overlap the gasket.

Install the head assembly over the guide pins. Be careful not to disturb the location of the intake valve. The compressor will not work if the valve overlaps the gasket and is pinched.

Carefully remove two of the guide pins and replace with two head capscrews and washers, if initially installed.

Tighten the two head capscrews.

Remove the remaining two pins and replace with two head capscrews and washers, if initially installed.

Tighten all five capscrews.

NOTE: The seal must be installed with the grooved side up.

Install the new rectangular V-seal into the unloader body.

Liberally lubricate the unloader valve bore above and below the rectangular ring seal with high temperature Accrolube Lubrication Teflon grease, or equivalent.

Install a new o-ring seal on the unloader valve body.

Use clean 15W-40 oil or Accrolube Lubrication Teflon Grease (or equivalent) to lubricate the seal.

Liberally lubricate the unloader valve body bore and unloader cap with high temperature Accrolube Lubrication Teflon grease, or equivalent.

Install the unloader cap.

Install the unloader spring.

NOTE: The two unloader body screws must not be used to attach any brackets.

Lubricate the unloader screw threads and under the head with clean engine oil (SAE 15W-40) before installation.

NOTE: The longer capscrews are used to mount the manifold to the air compressor.

Assemble the unloader components and attach the unloader assembly to the valve plate with the four capscrews and washers.