Cummins/Onan 6.5NH - 3CR / 6000 A — Valve Service
Repair & overhaul · Valves and seats
For the Cummins/Onan 6.5NH - 3CR / 6000 A, from the Cummins/Onan service manual.
Applies to: Cummins/Onan NH engine
Before you start
- Do not hand lap valves if avoidable; the sharp contact may be destroyed.
Procedure
- Remove the cylinder head; do not use a pry, rap the edge with a soft-faced hammer.
- Clean all carbon deposits from the cylinder head, piston top, valves and guides.
- Use a conventional valve spring lifter to remove the split type valve spring locks.
- Install a new valve if the face is burned or warped or the stem is worn.
- Worn valve stem guides may be replaced from inside the valve chamber; the smaller diameter of the tapered guides faces the valve head.
- Finish valve faces to 44 degrees and grind valve seats with a 45 degree stone, seat band 1/32 to 3/32 inch wide.
- Check each valve for a tight seat with an air pressure type testing tool or by pencil marks.
- Lightly oil the valve stems and reassemble; adjust the valve clearance.
Tools required
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
- Seat band 1/32 to 3/32 inch
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.