Cummins 4BT 3.9L STD Piston & Ring Set Kit (102mm) 4 Pistons w/ Rings, Pins &

It fits Cummins 4BT 3.9L using STD 102mm pistons. Always confirm by part number and bore size.

Yes — includes rings, wrist pins, and clips/retainers for all 4 pistons.

A: Typical ring gap ranges:
Top ring (turbo): ~0.40–0.70 mm (0.016"–0.027")
Second ring: ~0.25–0.55 mm
Oil ring: similar range depending on design

Always measure inside your cylinder using a feeler gauge before installation.

Stagger ring gaps 120° apart
Do NOT align gaps
Top ring and second ring have specific orientation (mark facing up)
Oil ring expander gap should not overlap rails

Yes:
Lightly oil:
Cylinder walls
Piston rings
Wrist pins
This prevents scoring and dry start damage.

No, use a proper ring compressor tool.
Improper installation can:
Break rings
Damage cylinder walls

Typical multi-step torque sequence (approx):
~26 ft-lb → 51 ft-lb → ~73 ft-lb progression
Always verify exact torque spec for your specific engine build.

Not checking ring gap
Installing rings upside down
Aligning ring gaps
Installing wrong size (STD vs oversize)
Not cleaning carbon ridge before install

STD (102mm): original bore, no machining
Oversize: if block was bored/honed
Always measure cylinder bore before ordering.

If cylinders are within spec → light hone is enough
If worn or out of round → machine work required