Cummins/Onan — Checking and Adjusting Valve Clearance
Adjustments · Cylinder head / rocker arms
From a Cummins/Onan operator's manual covering: 12.0MDJF-53CR, 12.0MDJF-53CR4, 12.0MDJF-54R, 12.0MDJF-55DR, 12.0MDJF-57R, 15.0MDJ F .. .4R 196 D, 15.0MDJF, 15.0MDJF-3CR, 15.0MDJF-3CR4, 15.0MDJF-5DR. Check it applies to your exact model before use.
Applies to: Cummins/Onan 12.0MDJF-53CR, Cummins/Onan MDJF (Onan J-series diesel) engine, Cummins/Onan MDJF engine
Procedure
- Turn flywheel until cylinder to be adjusted is on compression stroke (socket wrench on flywheel screw hex head).
- Turn flywheel clockwise an additional 10 to 45 degrees so piston is on power stroke with both valves closed.
- Loosen the rocker arm locknut to increase clearance; tighten to reduce clearance.
- Using a feeler gauge, check clearance between rocker arm and valve; set to .017 in intake and .017 in exhaust.
- Always adjust valve clearances in the firing order (1-2-4-3) sequence, rotating flywheel 180 degrees between cylinders.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- .017 in intake
- .017 in exhaust
- engine at room temperature (about 70 deg F)
Full service-parts list: Cummins/Onan 12.0MDJF-53CR →
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.