Cummins/Onan WC4-10S-5 — Valve Servicing
Repair & overhaul · Cylinder head and valves
For the Cummins/Onan WC4-10S-5, from the Cummins/Onan service manual.
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Before you start
- Major repairs should be attempted only by a mechanic thoroughly familiar with automotive type engines.
Procedure
- Drain the radiator and disconnect the fuel line at the carburetor.
- Remove the air cleaner, air cleaner tube and bracket assembly.
- Disconnect the throttle control rod and choke control from the carburetor; disconnect exhaust pipe and remove manifold.
- Remove spark plugs and disconnect the temperature gauge thermal element from the cylinder head; remove upper radiator hose.
- Remove cylinder head nuts holding the spark plug cable conduit and lay the conduit aside.
- Remove cylinder head and valve spring covers; pry down on top of a valve guide to remove retainer, then remove valve, guide and spring assembly upward.
- Remove carbon and corrosion; stem clearance in guide should be .0015 in to .0035 in; discard guide worn larger than .214 in.
- Reface valves to 45 degree angle; discard valves that become thin-edged or have worn stems.
- Clean all carbon from valve seats and ports and tops of pistons; reface hardened seat inserts if necessary (width not to exceed 3/32 in).
- Grind each valve in its seat with fine valve grinding compound; clean compound from all parts.
- Assemble valves; check valve-to-tappet clearance with tappet entirely down (.013-.015 in exhaust, .010-.012 in intake).
- Install valve spring covers using new gaskets; install cylinder head with a new gasket without cement.
- Tighten all head nuts to 50 ft-lbs with a torque indicating wrench.
- Complete reassembly in reverse order; install new radiator hose if needed and ensure thermostat arrow points toward radiator.
- Close drain cock, fill radiator, start the power unit and run without load to normal operating temperature; adjust carburetor and governor.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Valve stem clearance .0015 in - .0035 in
- Valve face angle 45 degrees
- Seat width max 3/32 in
- Cylinder head nuts 50 ft-lbs
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.