Cummins/Onan — Mechanical Governor Speed Adjustment

Adjustments · Mechanical governor (standard)

From a Cummins/Onan service manual covering: 4BT3.9, 4BT3.9-GC1, 4BT3.9-GC2, 6BT5.9, 6BT5.9-GC1, 6BT5.9-GC2, 6CT8.3, 6CT8.3-GS/GC1, 6CTA8.3, 6CTA8.3-GS/GC1, 6CTA8.3-GS/GC2. Check it applies to your exact model before use.

Applies to: Cummins/Onan 4BT3.9, Cummins/Onan 6BT5.9, Cummins/Onan 6CTA8.3, Cummins/Onan 4BT3.9 engine, Cummins/Onan 6BT5.9 engine, Cummins/Onan 6CT8.3 engine, Cummins/Onan 6CTA8.3 engine

Procedure

1. Use the frequency control meter (if equipped) or an accurate tachometer.
2. Loosen the speed adjustment screw locknut.
3. Start set, warm to operating temperature, then apply full rated load.
4. Adjust speed adjust screw in or out to reach required speed (60 Hz - 1800 r/min, 50 Hz - 1500 r/min).
5. Hold screw at proper setting and retighten locknut.
6. Remove and apply loads to check response; readjust if necessary.

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.

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