MMX 4-Pinned crank hub | BMW S55 | N55

MMX 4-Pinned Crank Hub – BMW N55 & S55

Upgrade one of the most important reliability points on your BMW N55 or S55 engine with the MMX 4-Pinned Single-Piece Crank Hub.

Designed for higher-power and heavily tuned applications, the MMX 4-Pinned Crank Hub replaces the factory three-piece crank hub arrangement with a single-piece billet steel hub that is mechanically locked to the crankshaft using four precision-machined dowels.

This provides a much more secure connection than the original friction-based arrangement and is intended for cars producing increased power and torque, particularly where the standard unpinned solution is no longer considered sufficient.

For highly modified N55 and S55 builds, the MMX 4-Pinned Crank Hub represents the most comprehensive crank hub solution in the MMX range.

Why Upgrade the N55 / S55 Crank Hub?

The factory N55 and S55 crank hub uses a three-piece design that relies heavily on friction between the individual components.

Under certain conditions, these friction interfaces can slip rotationally.

If the crank hub moves relative to the crankshaft, engine timing can shift away from its intended position.

In severe cases, this can result in:

• Incorrect camshaft timing
• Engine fault codes
• Poor engine operation
• Loss of performance
• Piston-to-valve contact
• Significant engine damage

The MMX 4-Pinned Crank Hub is designed to remove this weakness through both single-piece construction and direct mechanical location to the crankshaft.

Key Features

• MMX 4-Pinned Single-Piece Crank Hub
• Designed for BMW N55 and S55 engines
• Developed for high-power and high-torque applications
• Replaces the factory three-piece crank hub
• Single-piece construction
• Four-pin dowelled crankshaft location
• Four aerospace precision-machined dowels
• Mechanically locks the hub to the crankshaft
• Machined from heat-treated billet EN36 steel
• 0.75mm case hardened
• New OE crank bolt included
• Complete drilling and installation jig supplied
• HSS rolled high-speed drill bit included
• Optional MMX Capture Plate available
• Suitable for tuned, track and high-performance builds
• MMX part number MMR20-1004

Single-Piece Crank Hub Design

The first major improvement is the one-piece construction.

The original BMW hub relies on multiple components and friction interfaces.

The MMX hub replaces this with one solid billet component.

This removes the possibility of the individual hub sections rotating independently of one another.

Four-Pin Mechanical Location

The defining feature of this version is the four-pin dowelled mounting system.

Four precision-machined dowels physically locate the crank hub to the end of the crankshaft.

This means the hub is not relying solely on friction and crank bolt clamping force to maintain its position.

The dowels create a positive mechanical connection between the:

• Crankshaft
• Crank hub
• Timing drive assembly

This significantly increases security on engines producing higher power and torque.

Four Aerospace Precision-Machined Dowels

MMX supplies four precision-machined aerospace-grade locating dowels with the kit.

These are installed into accurately drilled holes at the crankshaft interface.

Once installed, the dowels mechanically prevent rotational movement between the crankshaft and hub.

This is what separates the pinned solution from the standard unpinned MMX one-piece crank hub.

Designed for Higher-Power Builds

MMX recommends its standard unpinned single-piece crank hub for Stage 1 tuned N55 and S55 engines.

For engines tuned beyond this level, MMX recommends the 4-pin version.

This makes the pinned hub particularly appropriate for:

• Stage 2 builds
• Upgraded turbo applications
• High-boost cars
• High-torque setups
• Hybrid turbo builds
• Track-focused vehicles
• Motorsport applications
• Heavily modified engines

For these applications, the additional mechanical location provides significantly greater security.

EN36 Billet Steel Construction

The MMX 4-Pinned Crank Hub is CNC-machined from billet EN36 steel.

The hub is then heat-treated and given approximately 0.75mm of case hardening.

This provides:

• High surface hardness
• Strong internal core material
• Excellent wear resistance
• High torsional strength
• Long-term durability

These characteristics make EN36 well suited to an engine component exposed to repeated high loads.

Eliminates Friction Plate Slip

The combination of single-piece construction and four-pin crankshaft location addresses the primary weakness of the factory hub.

With the MMX design:

• There are no separate hub sections to slip against one another
• The hub is positively located to the crankshaft
• Torque transmission is supported by the four dowels
• The crank bolt maintains clamping force across the assembly

This creates a much more secure timing-drive connection.

New OE Crank Bolt Included

A brand-new OE crank bolt is supplied with the kit.

MMX specifies the following installation procedure for the N55 and S55 crank bolt:

• Initial torque: 100Nm
• Followed by: 270 degrees additional rotation

Correct torque procedure is essential to maintaining clamping force across the assembly.

Complete Installation Jig Included

Because the crankshaft must be drilled accurately for the four locating dowels, installation requires specialist equipment.

MMX includes a complete installation jig with the kit to help ensure the crankshaft modifications are carried out accurately.

The kit includes:

• Bolt-on drilling guide
• Location bolt for the drilling guide
• HSS rolled high-speed drill bit

This helps a professional installer position and drill the crankshaft correctly.

Professional Installation Required

Installation of the MMX 4-Pinned Crank Hub is not a DIY job.

The crankshaft must be precision drilled to accept the locating dowels while the engine timing system is correctly locked and supported.

Professional installation by an experienced BMW specialist is strongly recommended.

The process requires:

• Engine timing tools
• Crankshaft locking tools
• Precision drilling
• Correct jig positioning
• Correct dowel installation
• Correct crank bolt torque procedure
• Verification of engine timing

Incorrect installation can result in serious engine damage.

MMX 4-Pinned Hub vs Standard One-Piece Hub

MMX offers two main crank hub solutions.

Standard Single-Piece Hub:

• One-piece billet construction
• Eliminates movement between factory hub sections
• No crankshaft drilling required
• Simpler installation
• MMX recommends it for Stage 1 tuned engines
• Part number MMR20-1001

4-Pinned Single-Piece Hub:

• One-piece billet construction
• Four mechanical locating dowels
• Requires precision crankshaft drilling
• Maximum mechanical security
• Recommended for higher-power and higher-torque engines
• Part number MMR20-1004

For heavily modified builds, the 4-pin version is the more appropriate option.

Optional MMX Capture Plate

The 4-Pinned Crank Hub can also be ordered with the MMX Crank Hub Capture Plate.

The Capture Plate performs a separate function.

While the pinned hub prevents rotational movement between the crankshaft and hub, the Capture Plate physically prevents the crank bolt from loosening.

Used together, they address both:

• Hub movement
• Crank bolt rotation

Maximum Crank Hub Security

Combining the MMX 4-Pinned Crank Hub with the MMX Capture Plate provides the most comprehensive crank hub setup offered by MMX.

The arrangement provides:

• Single-piece hub construction
• Four-pin crankshaft location
• New OE crank bolt
• Physical crank bolt retention

For high-output N55 and S55 builds, this represents the strongest MMX crank hub configuration.

Reliability-Focused Performance Upgrade

The 4-Pinned Crank Hub does not increase engine power.

Its purpose is to improve engine reliability while supporting higher power levels.

It is especially relevant for vehicles fitted with:

• ECU tuning
• Increased boost
• Hybrid turbochargers
• Upgraded turbo systems
• High-flow intakes
• Performance exhausts
• Track-focused engine modifications

As engine output increases, strengthening supporting components becomes increasingly important.

Ideal for Track & Motorsport Builds

Repeated high-rpm operation, aggressive throttle transitions and increased torque can place additional stress on the timing drive.

The MMX 4-Pinned Crank Hub is therefore particularly well suited to:

• Track-day cars
• Time Attack builds
• Motorsport vehicles
• High-power fast-road cars
• Drag-focused builds
• High-boost applications

BMW F20 / F21 M135i

The MMX 4-Pinned Crank Hub is compatible with applicable N55-powered BMW F20 and F21 M135i models.

For higher-power M135i builds, the pinned hub provides a stronger crank-to-hub connection than the standard factory arrangement.

BMW F22 / F23 M235i

The N55-powered BMW F22 M235i Coupe and F23 M235i Convertible are also supported.

For upgraded-turbo or high-boost M235i builds, the 4-Pinned Crank Hub provides additional timing-drive security.

BMW F30 / F31 335i

The MMX kit is suitable for compatible N55-powered BMW F30 and F31 335i models.

It is particularly relevant for highly modified or motorsport-oriented applications.

BMW F32 / F33 435i

The N55-powered BMW F32 435i Coupe and F33 435i Convertible are also supported.

For higher-output builds, the four-pin system provides a mechanical safeguard against hub rotation.

BMW F87 M2

The original BMW F87 M2 uses the N55 engine and is compatible with the MMX 4-Pinned Crank Hub.

For tuned, track-driven or upgraded-turbo F87 M2 builds, the pinned hub provides an important reliability upgrade.

BMW F87 M2 Competition

The BMW F87 M2 Competition uses the S55 engine and is also supported.

For high-power M2 Competition builds, the four-pin crank hub helps provide greater mechanical security under increased torque.

BMW F80 M3

The S55-powered BMW F80 M3 is compatible with the MMX 4-Pinned Crank Hub.

It is particularly appropriate for modified M3s running increased boost, upgraded turbos or regular track use.

BMW F82 M4

The BMW F82 M4 is also supported.

For tuned S55 applications, the MMX 4-Pinned hub provides a stronger foundation for higher-output engine builds.

BMW F83 M4 Convertible

The S55-powered BMW F83 M4 Convertible is also compatible.

Compatibility

Designed for applicable BMW N55 and S55 models including:

• BMW F20 M135i
• BMW F21 M135i
• BMW F22 M235i
• BMW F23 M235i Convertible
• BMW F30 335i
• BMW F31 335i Touring
• BMW F32 435i
• BMW F33 435i Convertible
• BMW F87 M2
• BMW F87 M2 Competition
• BMW F80 M3
• BMW F82 M4
• BMW F83 M4 Convertible

MMX lists fitment across F2X, F3X, F80, F82 and F87 chassis from 2011–2021 with N55 and S55 engines.

Please confirm exact vehicle and engine specification before ordering.

What's Included?

The MMX 4-Pinned Crank Hub Kit includes:

• MMX single-piece 4-pinned crank hub
• Heat-treated billet EN36 steel hub
• 4x precision-machined locating dowels
• New OE crank bolt
• Bolt-on drilling guide
• Drilling guide location bolt
• HSS rolled high-speed drill bit
• Required MMX-specific hardware

Optional MMX Capture Plate available separately or as a kit option.

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