Cummins/Onan JWC4-10S-3 — Grinding Valves
Repair & overhaul · cylinder head / valves
For the Cummins/Onan JWC4-10S-3, from the Cummins/Onan service manual.
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Before you start
- Do not drive a screwdriver or sharp instrument between cylinder head and block to break the head loose.
Procedure
- Drain radiator; disconnect governor oil supply line.
- Remove oil filter, fuel line, carburetor, choke controls, manifolds and ignition resistor.
- Remove upper radiator hose and spark plugs; lift cylinder head (use lifting hooks in No. 1 and 4 spark plug holes).
- Remove valve spring cover and screen.
- Compress valve springs, remove valve locks, valves and springs.
- Clean carbon from head, pistons, valve seats and valves; clean valve guides.
- Check valve stem-to-guide clearance; reface valves to 45 degree angle; replace worn parts.
- Touch up valves to seats by hand with fine valve grinding compound.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- .014 in valve tappet clearance
- Intake valve stem clearance .0015 to .00325 Amazon eBay $39.95 in
- Exhaust valve stem clearance .002 to .00375 in
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.