Cummins/Onan — Valve Service
Repair & overhaul · Valves
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MCCK
Before you start
- Do not use a pry to loosen the cylinder head.
- Do not hand lap valves.
Procedure
- Remove cylinder head; do not use a pry; rap sharply on edge with a soft-faced hammer.
- Use conventional valve spring lifter to remove split-type valve spring locks.
- Clean all carbon deposits from cylinder head, piston top, valves, guides, etc.
- If valve face is burned or warped, or stem worn, install new valve.
- Worn valve stem guides may be replaced from inside valve chamber; seal behind intake valve guides only.
- Smaller diameter of tapered valve guides must face toward valve head.
- Tappets are replaceable from valve chamber after removing valve assemblies.
- Valve face angle is 44 degrees; valve seat angle is 45 degrees; do not hand lap.
- Finish valve faces in machine to 44 degrees; grind seats with 45 degree stone; seat band width 1/32 to 3/64 inch (0.79-1.2 mm).
- Grind only enough to assure proper seating.
- Remove all grinding compound; place each valve in its proper location.
- Check each valve for tight seat using air pressure type testing tool or pencil marks.
- Lightly oil valve stems and reassemble all parts; adjust valve clearance.
Tools required
- soft-faced hammer Amazon
- valve spring lifter Amazon
- 45 degree stone Amazon
- air pressure type testing tool Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Valve face angle: 44 degrees
- Valve seat angle: 45 degrees
- Valve seat band width: 1/32 to 3/64 inch (0.79-1.2 mm)
Full service-parts list: Cummins/Onan MCCK →
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.