This guide covers installation of the XOTIC PERFORMANCE™ CP877 head stud kit for the 2001–2016 6.6L Chevrolet/GMC Duramax — all five generations: LB7, LLY, LBZ, LMM, and LML. It covers the three-stage M12 torque specs, the separate upper row M8 bolt procedure, and the prep steps that determine whether your head gaskets seal. Prefer a printable copy? Download the PDF manual.

Why the 6.6L Duramax needs head studs

Factory OEM head bolts are torque-to-yield: you torque them to a specified value, then add a final 90° rotation that stretches the bolt to its maximum point. That works at stock power levels. But when you add parts that increase horsepower — a turbocharger, injectors, a tuner — you create higher cylinder pressures lower in your RPM range, and the clamping force securing the gasket, head, and block is no longer sufficient. The result: a blown head gasket.

Head studs are engineered to resist stretching. XOTIC PERFORMANCE™ head studs are manufactured from our premium XOTIC 7200 steel alloy, superior in tensile strength to any bolt, and backed by a lifetime warranty. The key to getting that strength into your engine is accurate preload — the tensile force generated when a fastener is tightened, creating clamp force in the joint. Everything in this guide is in service of achieving equal, accurate preload across all 36 studs and 8 upper row bolts.

What's in the CP877 kit

• 36 × M12 head studs (XOTIC 7200 alloy)
• 36 × hardened parallel washers
• 36 × nuts
• 8 × upper row M8 bolts
• 2 × sockets
• 1 × allen wrench
• 1 × fastener assembly lubricant

Before you start: verify first

Confirm that part number CP877 is compatible with your application (2001–2016 6.6L Duramax — LB7, LLY, LBZ, LMM, or LML) before installing any components. Inspect all package contents and clean as necessary to ensure accurate installation. Report any obvious defects or shipping damage to us before proceeding.

How to install head studs on a 6.6L Duramax

1. Clean the block threads. Clean the threads in the block prior to installing the head studs to ensure accurate fitment and precise torque readings. Dedicated thread chasers make this fast and protect the threads: M12 x 1.5 (CS303) for the stud holes and M8 x 1.25 (CS317) for the upper row bolt holes.
2. Install the studs hand-tight. Thread the head studs into the block by hand until snug. Do not apply torque.
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. Set the gasket and head. Install the head gasket and cylinder head, ensuring proper alignment.
5. Clean the washer seating areas. Clean the washer seating surfaces on the cylinder head with a fast-evaporating solvent such as non-chlorinated brake cleaner to remove oil, grease, and contaminants. A clean surface is essential for achieving proper fastener preload.
6. Lubricate. Place the washers onto the studs. Using the supplied assembly lubricant, apply a thin coat to the stud threads, the underside of the nuts, and the top side of the washers.
7. Install the nuts and torque the M12 studs. Thread the nuts onto the studs and hand-tighten until they make contact with the washers, then follow the M12 torque stages below in the numbered sequence shown in the manual's torque sequence diagram.
8. Install the upper row M8 bolts. Apply assembly lubricant to the threads and the seating surface of the upper row M8 bolts. Install them using the M8 torque sequence shown in the manual, tightening in two stages from the center outward.

6.6L Duramax head stud torque specs

M12 head studs (three stages)

Upper row M8 bolts (two stages, center outward)

Frequently asked questions

What are the torque specs for 6.6L Duramax head studs?

M12 studs: three stages — 45 ft-lbs, then 90 ft-lbs, then a final pass at 125 ft-lbs, following the numbered sequence. Upper row M8 bolts: two stages — 10 ft-lbs, then 25 ft-lbs, working from the center outward.

Which Duramax generations does the CP877 kit fit?

All 2001–2016 6.6L Duramax engines: LB7, LLY, LBZ, LMM, and LML, in Chevrolet, GMC, and Hummer applications.

What are the upper row M8 bolts for?

The Duramax uses eight smaller M8 bolts along the upper row of each head in addition to the main studs. They install after the M12 studs are fully torqued, with lubricant on both the threads and the seating surface, in two stages from the center outward.

What size thread chaser do I need for a Duramax head stud install?

Two sizes: M12 x 1.5 (CS303) for the head stud holes and M8 x 1.25 (CS317) for the upper row bolt holes.

Doing the full engine?

If the heads are off, it's the cheapest time you'll ever have to do the bottom end. The Head & Main Stud Combo Kit (CP877-MP881) pairs these head studs with main studs for the 2006–2010 LB7/LMM. Running a 2001–2005 LB7/LLY? Grab the MP877 main stud kit; for 2006–2010, the MP881 kit.

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: 2025.05.27 (web edition 2026.08).