Cummins/Onan — Cylinder heads and valves - disassembly
Repair & overhaul · Cylinder head / valve assemblies
From a Cummins/Onan service manual covering: 10.0JC, 12.5JC, 15.0JC, 4.0JB, 5.0JB, 6.0JB, 6.1JB, 7.5JB, 7.6JB. Check it applies to your exact model before use.
Applies to: Cummins/Onan 10.0JC, Cummins/Onan 12.5JC, Cummins/Onan 15.0JC, Cummins/Onan 5.0JB, Cummins/Onan 6.0JB, Cummins/Onan 6.1JB, Cummins/Onan 7.5JB, Cummins/Onan 7.6JB, Cummins/Onan JB engine, Cummins/Onan JC engine
Before you start
- Valves, tappets, rocker arms and pushrods should be kept in order and returned in same order
Procedure
- Remove rocker box cover, spark plugs and connecting oil lines; remove intake and exhaust manifold
- Remove capscrews holding each cylinder head to the cylinder block
- Remove each head; if it sticks rap sharply with a soft hammer, don't use a pry
- Remove the rocker arms and pushrods
- Using a valve spring compressor, disassemble the valve assemblies
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Full service-parts list: Cummins/Onan 10.0JC →, Cummins/Onan 12.5JC →, Cummins/Onan 15.0JC →, Cummins/Onan 5.0JB →, Cummins/Onan 6.0JB →, Cummins/Onan 6.1JB →, Cummins/Onan 7.5JB →, Cummins/Onan 7.6JB →
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.