Kooks LS Engine Header Bolts and Locking Hardware Qty 12 - M8 - 1.25 x 25mm Bolts

12 Piece Stage 8 Locking Header Bolt Kit That Keeps GM LS Engine Headers Sealed Permanently

The BK110 is a 12 piece Stage 8 locking header bolt kit designed for GM LS engines, using M8 by 1.25 by 25mm fasteners with the Stage 8 positive mechanical locking hardware system. LS engines are among the most popular platforms for long tube header installation in the performance community, and header bolt loosening is one of the most frequent complaints that follows a header installation that used standard fasteners. The thermal cycling of a performance exhaust system, combined with the inherent vibration of a V8 engine, works loose conventional bolts over time even when thread locker is applied. This bolt kit eliminates this problem with a fastener system designed specifically for this exact application.

Stage 8 locking hardware uses a positive mechanical retainer clip that physically prevents the bolt from rotating after installation, independent of friction, thermal state, or torque preload. The BK110 covers the complete 12 bolt LS cylinder head header flange pattern in a single kit, so there is no counting or sourcing individual bolts from a hardware store. Using the correct M8 by 1.25 by 25mm length also ensures the bolt engages the correct number of threads in the LS head without bottoming out before clamping, which is a common failure mode when builders use improperly specified fasteners. Order this bolt kit with your Kooks LS headers and install it right the first time.

Key Features

• 12 piece complete kit for GM LS engine cylinder head header flange
• Stage 8 positive mechanical locking system prevents bolt back out
• M8 by 1.25 by 25mm specification correct for LS exhaust port bolt holes
• No thread locker required; mechanical lock is independent of friction
• Resists loosening under thermal cycling and engine vibration
• Designed for use with Kooks LS long tube headers

What's Included

• 12 x Stage 8 locking header bolts, M8 by 1.25 by 25mm
• 12 x Stage 8 locking retainer clips

Specifications

Frequently Asked Questions

What LS engines does this bolt kit fit?
This bolt kit uses the M8 by 1.25 by 25mm specification that is correct for GM LS cylinder heads across the LS family, including LS1, LS2, LS3, LS6, LS7, LS9, LSA, and LSX based engines. Verify your specific application with Kooks if you have an unusual head casting.

Why do LS header bolts loosen after installation?
LS engines produce significant heat at the cylinder head and header flange interface, and the stainless steel headers expand and contract through a wide temperature range. This thermal cycling, combined with engine vibration, gradually releases the clamp load on standard fasteners, causing them to back out and allow exhaust leaks.

How does Stage 8 locking hardware prevent back out?
Stage 8 hardware uses a retainer clip that locks into the bolt head and a fixed point on the header flange, creating a physical barrier against rotation in the loosening direction. The bolt cannot back out unless the retainer clip is manually removed.

Does this bolt kit include 12 bolts for both banks?
Yes. The LS cylinder head uses six exhaust port bolt positions per bank, for 12 total on a V8. This bolt kit kit includes 12 bolts and 12 retainer clips for the complete installation.

Do I need thread locker with this bolt kit?
No. Thread locking compound is not needed and is generally not recommended with Stage 8 hardware. The mechanical lock retainer clip is the primary anti loosening mechanism.

What happens if I lose a retainer clip during installation?
Replacement Stage 8 retainer clips are available separately from Stage 8 Fasteners. Do not operate the vehicle with header bolts lacking their retainer clips.

Can this bolt kit bolts be reused after header removal?
The bolts themselves can be reused if they are not damaged during removal. Retainer clips should be inspected for deformation and replaced if there is any doubt about their condition.

Will this bolt kit work with headers from other manufacturers?
The M8 by 1.25 by 25mm specification matches standard LS header flange dimensions. Compatibility with non Kooks headers depends on the flange bolt hole diameter and clearance for the Stage 8 retainer clip. Verify before ordering.

What is the torque specification for this bolt kit bolts?
Refer to your Kooks header installation instructions for the correct torque specification. As a general reference, GM LS exhaust manifold bolts are typically torqued in the range of 11 to 15 ft lb, but follow the Kooks specification for header applications.

Is this bolt kit different from the BK111?
Yes. This bolt kit is for GM LS engines and includes 12 pieces. The BK111 is for Dodge HEMI engines and is a separate kit with a different quantity and application.

Installation Instructions

1. Clean the LS cylinder head exhaust port flange bolt holes of any old thread locker, rust, or debris.
2. Install new header gaskets on the cylinder head exhaust port surfaces.
3. Position the Kooks LS headers against the cylinder heads with gaskets aligned.
4. Thread all 12 this bolt kit M8 by 1.25 by 25mm bolts by hand before applying torque to any of them.
5. Torque all bolts to the Kooks header installation specification in a crossing pattern, typically starting from the center and working outward.
6. Install each Stage 8 retainer clip onto the corresponding bolt head, securing it to the header flange per Stage 8 instructions.
7. Verify all 12 retainer clips are fully seated before starting the engine.
8. Check bolt tightness after the first heat cycle.

Prop 65 Warning

WARNING: This product can expose you to chemicals known to the State of California to cause cancer, birth defects or reproductive harm. For more information go to www.P65Warnings.ca.gov.