Cummins/Onan — Cylinder Head Assembly
Repair & overhaul
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Protect head sealing surface against marring.
Procedure
- Install pipe plugs, fittings, and cup plugs.
- Dip valve stems in clean engine oil.
- Insert valves into guides.
- Place lower valve spring seat and spacer(s).
- Place spring and upper spring seat.
- Compress valve spring and install new half collets.
- Release tension and check collets seated.
- Remove spring compressor.
Tools required
- ST-448 valve spring compressor Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
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.