Kohler — Rotor Test Procedure
Testing & diagnosis · Main field (rotor)
From a Kohler service manual covering: 12RES, 8.5/12 RES, 8.5RES. Check it applies to your exact model before use.
Applies to: Kohler 12RES, Kohler 8.5RES, Kohler CH20 engine, Kohler CH 740 engine
Before you start
- High voltage test. An improper test procedure can damage equipment or lead to generator set failure.
Procedure
- Place master switch in OFF; disconnect battery charger power; disconnect battery negative lead first.
- Remove the brush cover from the alternator end bracket.
- Check rotor continuity and resistance; raise brushes from slip rings during ohmmeter tests.
- Measure the rotor resistance in ohms between the two slip rings.
- Perform a megohmmeter test to determine whether rotor is shorted to ground.
- Raise and secure the brushes away from slip rings with a retaining wire in the brush holder hole.
- Apply 500 volts DC to one rotor slip ring and the rotor poles or shaft.
- A reading of approximately 500 kOhms or higher indicates a good rotor.
- Repair or replace the rotor if the reading is less than approximately 500 kOhms.
- Remove retainer wire, check brush positions, and reinstall the brush cover.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Rotor resistance, cold, 4.0 ohms
- Good reading 500 kOhms or higher at 500 VDC
Full service-parts list: Kohler 12RES →, Kohler 8.5RES →
Source: Kohler 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.