Cummins/Onan JWC4-10S-3 — Setting Valve Timing
Adjustments · timing chain and sprockets
For the Cummins/Onan JWC4-10S-3, from the Cummins/Onan service manual.
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Procedure
- Turn crankshaft so No. 1 or No. 4 pistons are at top dead center (TC mark visible through flywheel housing hole).
- Place camshaft sprocket on camshaft and start the four capscrews by hand.
- Rotate camshaft so punch mark on sprocket aligns with punch mark on crankshaft sprocket.
- Remove sprocket, install timing chain, and re-position sprocket in chain until capscrew holes match.
- Verify punch marks align on a straight line between sprocket centers.
- Tighten capscrews and lock with special washers.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Inlet valve opens 9 degrees before top center (.039 inch piston travel)
- No. 4 cylinder at top of compression stroke
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.