Cummins/Onan B43 / B48 — Piston Assembly and Installation in Cylinder

Repair & overhaul · pistons

For the Cummins/Onan B43 / B48, from the Cummins/Onan service manual.

Applies to: Cummins/Onan B48

Procedure

1. Lubricate all parts with engine oil.
2. Position piston on its respective rod and install the pin.
3. Install the rings on the pistons starting with the oil control ring; use a piston ring spreader.
4. Compression rings have a dot or the word 'top' on one side indicating which side faces the top of the piston.
5. The oil control ring expander ends should butt with the joint 180 degrees from the gap of that ring.
6. Turn crankshaft to position number one rod bearing journal at bottom of its stroke.
7. Lubricate the number one piston assembly and inside of the cylinder; compress rings with a ring compressor.
8. Position the piston and rod assembly in the cylinder block; notched side of connecting rod must face camshaft.
9. Tap the piston down with the handle end of a hammer until the connecting rod is seated on the journal.
10. Install the bearing cap; install one fastener and tighten to 5 ft-lbs (7 Nm), repeat for the other fastener, then tighten both to 14 ft-lbs (19 Nm).
11. Install the remaining piston and rod in the same manner; crank the engine over by hand to check bearings are free.
12. Install the oil base with a new gasket; install the cylinder heads; replace oil and break in engine.

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.

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