Cummins/Onan B43 / B48 — Oil By-Pass Valve Inspection
Adjustments
For the Cummins/Onan B43 / B48, from the Cummins/Onan service manual.
Applies to: Cummins/Onan B48
Procedure
- Remove the 3/8 x 24 x 7/8 cap screw located behind gear cover and under governor arm.
- Remove spring and plunger with a magnet tool.
- Check spring and plunger per measurements: plunger diameter 0.3105 to 0.3125 in (7.89 to 7.94 mm); spring free length 1.00 inch (25.4 mm); load 2.6 +/- 0.2 lbs (11.6 +/- 0.9 N) compressed to 0.5 inch
- Check valve seat and clean away any accumulation of metal particles.
- Verify valve seat is concentric with larger diameter valve bore.
- Clean plunger and spring in parts cleaning solvent and install.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Valve begins to open about 20 psi (138 kPa); valve is non-adjustable
Full service-parts list: Cummins/Onan B48 →
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.