BMW S55 Crank Hub Upgrade Kit | One-Piece & 4-Pin

BMW S55 Crank Hub Upgrade – One-Piece 4-Pin Design

Crank hub slip is a known concern on BMW S55 engines and can also affect certain N55 applications. If the crankshaft hub moves relative to the crankshaft, the resulting timing deviation can cause fault codes, poor engine operation and, in severe cases, internal engine damage.

The factory multi-piece crank hub relies on friction between its components to transmit torque. Under demanding operating conditions, particularly on modified engines producing higher power and torque this friction-based arrangement can become a concern.

Our one-piece 4-pin crank hub upgrade is manufactured from hardened 4340 alloy steel. The integrated sprocket design eliminates the separate internal friction interface found in the original multi-piece hub while four locating pins provide an additional mechanical connection between the hub and crankshaft.

This design is intended to reduce the risk of crank hub slip and improve timing-drive security particularly on higher-output S55 builds. (800 WHP+) Correct installation crankshaft preparation and bolt tightening remain essential to the reliability of the assembly.

Key Features

• One-piece crankshaft hub with integrated sprocket design
• Hardened 4340 alloy steel construction
• Four-pin mechanical location between the hub and crankshaft
• Suitable for professional installation on compatible S55 and N55 applications
• Precision drilling of the crankshaft is required

Vehicle Fitment

• BMW M2 Competition / M2 CS (F87) – S55
• BMW M3 (F80) – S55
• BMW M4 (F82 / F83) – S55
• BMW M2 (F87) – N55, subject to confirmation of the correct hub and crankshaft bolt

Please confirm engine compatibility before ordering. N55 and S55 applications may require different installation hardware, and the correct crankshaft bolt must be used for the engine being fitted.

What Is Included?

• One-piece 4-pin crankshaft hub upgrade
• Genuine BMW M18 crankshaft stretch bolt for the applicable S55 installation
• Drilling fixture and supplied drill bits for the crankshaft modification

The drilling fixture is designed to assist with accurate positioning of the locating holes. Professional installation is required, and the crankshaft must be correctly timed and secured before drilling.

Tightening Torque

S55 crankshaft hub central bolt (M18): 100 Nm + 270°.

This is a reference specification only. Always verify the latest BMW workshop procedure and the instructions supplied with the particular hub and bolt before installation. Use a new, correct-specification stretch bolt and follow the specified tightening sequence and preparation requirements.

Where a bolt-locking flange or other optional accessory is fitted, tighten its fasteners to the specification supplied for that exact component. Do not assume that torque settings from another crank hub or locking-flange kit are interchangeable.

Understanding BMW S55 Crank Hub Failure

The original crank hub arrangement uses friction surfaces to maintain the relationship between the crankshaft and timing-drive components. If sufficient movement occurs, the engine's valve timing can be affected.

Several aftermarket solutions are available, including multi-piece, splined, keyed and pinned designs. Their construction, installation requirements and intended applications differ, so they should not be treated as equivalent. The important distinction with our upgrade is its integrated one-piece construction combined with four-pin mechanical location.

The photographs below illustrate examples of crank hub-related damage and the importance of selecting and installing the correct solution for the intended engine build.

4-Pin S55 Crank Hub Upgrade with Drilling Fixture

The four-pin arrangement provides a positive mechanical location between the crankshaft and the replacement hub. This supplements the clamping force of the central bolt and is intended to reduce the possibility of relative movement at the hub-to-crankshaft interface.

Correct positioning and timing are essential before drilling. The fixture must be installed according to the kit instructions, and the crankshaft must be properly secured. Incorrect drilling, pin fitment or assembly can damage the crankshaft or compromise the installation.

BMW S55 Crank Hub Pin Alignment and Drilling Procedure

Installation requires precision drilling of the crankshaft and should be carried out by an experienced BMW engine specialist. The following information is a general overview and does not replace the kit-specific instructions or BMW workshop procedures.

Aligning the Crank Hub Drill Fixture

Position the drilling fixture according to the supplied instructions. Ensure the locating surfaces are clean, the fixture sits fully against the hub without rocking, and all locating and securing hardware is correctly fitted. Verify the engine timing and fixture alignment before drilling.

Drilling with the Supplied Drill Bits

Use the supplied drill bits and follow the specified drilling sequence, depth and cutting requirements. Maintain accurate alignment through the fixture, use suitable cutting lubricant where specified, and control swarf to prevent contamination of the engine. Do not attempt to correct an incorrectly positioned fixture by angling the drill.

Checking the Pin Fit Before Assembly

After drilling, remove all swarf and thoroughly clean the machined areas. Check the locating-pin fit and confirm that the hub seats correctly without forcing any misaligned components. Follow the kit-specific instructions for final assembly, bolt tightening and timing verification.

Because the installation involves modification of the crankshaft, we strongly recommend fitting by a workshop experienced with BMW S55/N55 timing systems and crank hub upgrades.

Optional Upgrade

The following option is available when selected above the Add to Cart button:

• Front crankshaft seal guard – an optional addition to the crank hub upgrade kit.