Head Bolt 3.9 4B/4BT 5.9 6B/6BT Cummins

New Cylinder Head Bolt 3.9 4B/4BT 5.9 6B/6BT Cummins Engines.

This is a 12mm Hexagon Flange Bolt M12 x 1.75 x 120mm or 12 mm x 120 mm.

Also fits some QSB4.5 engines.

This is the medium sized head bolt. The 4BT engine takes 10 of these bolts and the 6BT takes 14 of them.

Scroll down for more detailed compatibility information.

Part Number: 3903939 3920780

Weight: 0.5 lbs.

Price: $3.00

Short Product Description:

3903939 Cylinder Head Bolt

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Questions and Answers:

Q: What is a complete head bolt set for the 4BT 8v and 6BT 12v engines?	11/18/2024
A: If you have a 4B engine, then you need 4 of 3920781, 4 of 3920779 and 10 of 3920780. If you have a 6B engine, then you need 6 of 3920781, 6 of 3920779 and 14 of 3920780.
Q: How should I tighten the head bolts on 4BT 8v and 6BT 12v cylinder heads?	1/29/2025
A: According to the Haynes Repair Manual the cylinder head bolts should first be tightened to 66 ft-lbs. Start with the middle bolts and then the outer bolts. Then the longer rocker arm head bolts should be tightened to 89 ft-lbs of torque. Then all the bolts should be tightened an additional 90 degrees. This is done from the inside bolts first, and then the outer bolts.

Description: 3903939 Cylinder Head Bolt

Price: $3.00