3.9L 4BT Cummins Main Stud Installation Guide (1983–1998) — CP884

This guide covers installation of the XOTIC PERFORMANCE™ CP884 main stud kit for the 3.9L 4BT four-cylinder Dodge Cummins. Prefer a printable copy? Download the PDF manual.

Why a 4BT needs main studs

The 4BT was built as an industrial and delivery-truck engine, which is why it ends up in everything from Jeeps to swapped pickups — it is enormously durable at its designed output. The trouble is that almost nobody leaves one at its designed output. A P-pump turned up, a bigger turbo, or a swap that finally lets the engine rev means the bottom end is seeing loads Cummins never specified, and with only four cylinders the power pulses arriving at each main cap are big and widely spaced.

Main cap fasteners are what keep the crankshaft bearing bores round and located under that load. Studs handle it better than bolts for a structural reason: a bolt is torqued into the block, so it twists and stretches at the same time, while a stud is threaded in finger-tight and stays still while the nut is torqued against it — loading the stud in pure tension. That gives more consistent, more accurate preload — the tensile force in the fastener that becomes clamp force in the joint — which is what stops cap walk and bore distortion. XOTIC PERFORMANCE™ main studs are manufactured from our premium XOTIC 7200 steel alloy and backed by a lifetime warranty.

What's in the CP884 kit

• 10 × main studs (XOTIC 7200 alloy)
• 10 × hardened parallel washers
• 10 × nuts
• 1 × socket
• 1 × allen wrench
• 1 × fastener assembly lubricant

Before you start: verify first

Confirm that part number CP884 is compatible with your application before installing any components. Inspect all package contents for damage and clean as necessary to ensure accurate installation. Report any obvious defects or shipping damage to us before proceeding.

How to install main studs on a 3.9L 4BT Cummins

1. Chase the block threads. Clean the threads in the block with a thread chaser prior to installing the studs, to ensure accurate fitment and precise torque readings. The correct tool here is the M14 x 2.0 chaser (CS301), available separately.
2. Thread the studs in by hand. Screw the main studs in as tight as can be made by hand — no tool necessary, and do not apply torque. Loctite may be used for permanent stud installation, but the fasteners must be fully torqued before the Loctite sets.
3. Check stud height with a straightedge. Use a straightedge ruler to measure the distance from the mating surface (deck or main cap) to the top of each installed stud. Ensure all studs of the same length group sit level with each other (within 1 mm / 0.040”). Uneven height may indicate debris or incorrect thread engagement. Properly installed studs will bottom out smoothly and show uniform height across all positions. If a stud appears higher or lower than the others, remove it, re-clean the hole, and reinstall by hand. Do not use tools to force studs deeper. Incorrect stud seating can cause off-angle stress, uneven preload, or stud fracture during engine operation.
4. Install the main caps. Set the caps in place and ensure appropriate alignment before any load goes on them.
5. Lubricate. Using the fastener assembly lubricant included in the package, lubricate the threads of the main studs and the nuts.
6. Hand-tighten the nuts. Thread the nuts onto the studs as tight as can be made by hand.
7. Torque in three equal steps. Working in the sequence shown in the manual's torque sequence diagram, tighten the nuts through the three stages below. Never go straight to the final value.
8. Check the bores. With the studs torqued, check the main bores for size and roundness. If an align hone is needed, do it with the same fasteners and lubricant that will be used during final assembly, at the specified torque.

4BT Cummins main stud torque specs

Frequently asked questions

What are the main stud torque specs for a 3.9L 4BT Cummins?

60 ft-lbs, then 120 ft-lbs, then a final 175 ft-lbs — three equal steps, following the sequence in the manual.

Do I need to align hone after installing 4BT main studs?

Check first, then decide. Once the studs are torqued, measure the main bores for size and roundness. Studs clamp the caps differently than the factory bolts did, so a bore that measured round with bolts may not be. If it needs honing, do it with the same studs, nuts, and assembly lubricant you'll use for final assembly, torqued to spec.

What thread chaser does the 4BT block take?

The M14 x 2.0 chaser (CS301). Chasing is not tapping — a chaser cleans existing threads without cutting new material, which is exactly what you want in a main web.

Should the studs be torqued into the block?

No. Thread them in finger-tight only. The advantage of a stud is that it isn't twisted while it's stretched — torquing the stud into the block gives that away and skews your preload.

Doing the whole 4BT?

If the engine is on the stand, the deck and the rods deserve the same hardware. See our 4BT head stud guide (CP896) and the 4BT connecting rod bolts (CR100).

Need help?

For technical support, email support@xotic-performance.com. All XOTIC PERFORMANCE™ fasteners are covered by our limited lifetime warranty. Finished your install? Tag #XOTICPERFORMANCE on Instagram for a chance to be featured.

© 2026 XOTIC PERFORMANCE™. This installation guide is an original copyrighted work of XOTIC PERFORMANCE™. Reproduction, distribution, or use of this content in whole or in part without written permission is prohibited. Doc ref: 2025.05.20 (web edition 2026.08).