Cummins/Onan — Decompression Release Adjustment (MDJA)
Adjustments
From a Cummins/Onan operator's manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MDJA, Cummins/Onan MDJC
Before you start
- If the screw is tightened more than 1 turn, the exhaust valve could hit the piston.
Procedure
- Set valves to correct clearance and leave flywheel at 10° ATC.
- Set the arm in the decompression position.
- Turn the set screw so the end just touches the exhaust rocker arm.
- Turn the screw exactly 1 revolution clockwise.
- Hold the set screw and tighten the lock nut hand tight, then 1/4 to 1/2 turn farther.
- Release the mechanism and check clearance between screw and rocker arm.
Tools required
- Feeler gauge Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 10° ATC; 1 revolution clockwise.
Full service-parts list: Cummins/Onan MDJA →, Cummins/Onan MDJC →
Source: Cummins/Onan operator's 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.