Cummins/Onan — Replacing the Serpentine Belt
Maintenance · Serpentine belt drive
From a Cummins/Onan owner's manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MDDC, John Deere 4045TFM engine, John Deere 6068TFM engine
Before you start
- Disconnect negative battery cable before removing access door or belt guard.
Parts for this job
Part numbers from the service-parts lists for Cummins/Onan MDDC, John Deere 4045TFM engine. Verify against your serial number before ordering; some links are affiliate links.
Procedure
- Disconnect negative battery cable with insulated wrench.
- Remove belt guard or enclosure end panel.
- Disconnect PTO shaft if equipped.
- Relieve belt tension by rotating tensioner pulley arm counterclockwise with a 15 mm wrench; remove belt.
- Check tensioner, idler, alternator, and coolant pump pulleys for smooth rotation.
- Check tensioner arm for smooth operation through travel.
- Install belt with each V in its proper groove.
- Check tensioner arm is about midway between end stops.
- Replace belt guard or end panel.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Tensioner arm should be about midway between end stops
Full service-parts list: Cummins/Onan MDDC →, John Deere 4045TFM engine →
Source: Cummins/Onan owner'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.