Cummins/Onan — Alternator Assembly (PTO and Two Bearing)
Repair & overhaul · YD PTO / Two Bearing alternator
From a Cummins/Onan service manual covering: 15.0YD-3G, 20.0YD-3G, 20.0YD-5DG, 25.0YD-3G, 25.0YD-5DG, 30.0YD-3G, 30.0YD-5DG, 6.0-3CS1, 7.5-3CS1. Check it applies to your exact model before use.
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Procedure
- Clean and inspect all mating surfaces.
- Coat mating area between alternator bearing and end bell bearing hole with a thin film of Molykote.
- Install rotor-through-stud in drive pinion shaft if removed.
- Install rotor and fan assembly on adapter.
- If removed, install exciter rotor and shaft bearing; torque shaft nut against exciter rotor 130 to 150 ft. lbs. (176 to 203 Nm).
- Install two stator through-studs in adapter for aligning.
- Install baffle ring.
- Install remaining two stator through-studs.
- Install stator and end bell; torque nuts 19 to 21 ft-lbs (26 to 28 Nm).
- Torque down rotor-through-stud nut to 55-60 ft. lb (75-81 Nm).
- Install mounting feet and control box.
- Connect alternator output and control leads.
- Replace end bell cover and control box cover.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Shaft nut against exciter rotor: 130 to 150 ft. lbs. (176 to 203 Nm)
- Stator through-stud nuts: 19 to 21 ft-lbs (26 to 28 Nm)
- Rotor-through-stud nut: 55-60 ft. lb (75-81 Nm)
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.