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Home›Repair guides›Cummins/Onan›Cylinder Head Decarbonize

Cummins/Onan — Cylinder Head Decarbonize

Maintenance

From a Cummins/Onan service manual covering: 4.5 MCE, 5.0 MCE, 6.5 MCE. Check it applies to your exact model before use.

Applies to: Cummins/Onan 4.5 MCE, Cummins/Onan 5.0 MCE, Cummins/Onan 6.5 MCE, Cummins/Onan MCE engine

Procedure

  1. Drain engine coolant and disconnect coolant hoses from cylinder heads.
  2. Remove cylinder head bolts and pull off cylinder heads.
  3. Remove carbon deposits with a wire brush.
  4. Install new head gaskets.
  5. Reinstall heads, torquing bolts in sequence in steps of 5 ft-lbs to 29-31 ft-lbs.
  6. Reconnect hoses and refill engine with coolant.
  7. Retorque head bolts when set has run 25 hours.

Tools required

Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.

Specs & values

  • Head bolt torque 29-31 Amazon eBay ft-lbs (39-42 Nm)

Full service-parts list: Cummins/Onan 4.5 MCE →, Cummins/Onan 5.0 MCE →, Cummins/Onan 6.5 MCE →

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.

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