Cummins/Onan — Main Bearings
Repair & overhaul
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Avoid overheating.
Procedure
- Main bearings are sleeve type babbitt faced, steel backed, not flanged.
- Crankshaft main bearings precision type available standard, .002, .010, .020, .030 inch undersize.
- Precision type do not require line reaming.
- Use press or drive plug to remove. Support cylinder block to avoid distortion.
- Warm bearing plate and cylinder block slightly with hot water or oven at 200°F.
- Align oil hole in bearing with oil passage hole in bearing bore.
- Install cold precision bearing so inside end is 1/16 to 3/32 inch back from inside end of bore.
- Adjust crankshaft end play with gaskets between rear bearing plate and cylinder block.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- undersizes .002, .010, .020, .030 inch
- inside end 1/16-3/32 inch back
- end play .010-.015 inch
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.