Why do N55 and S55 crank hubs fail, and what does the BMW N55 S55 crank hub upgrade fix?

The factory N55 and S55 crank hub is a three-piece design that relies on friction between plates to hold the hub in correct timing alignment. Under elevated power and torque, that friction can be overcome, allowing the hub to slip rotationally on the crankshaft — pulling ignition timing out of alignment and in the worst case causing piston-to-valve contact. The MMX BMW N55 S55 crank hub replaces the three-piece assembly with a single-piece billet EN36 steel hub pinned to the crankshaft with four dowel pins, making rotational slip physically impossible.

What is included in the BMW N55 S55 crank hub kit?

The complete kit includes the billet EN36 steel single-piece hub, four precision dowel pins, a new OE crank bolt, and the full installation jig — a bolt-on drilling guide, location bolt, and high-speed drill bit — to ensure accurate dowel placement during installation.

Do I also need the MMX Capture Plate?

The Capture Plate and the BMW N55 S55 crank hub address two separate but related failure modes. The crank hub upgrade prevents hub-to-crank rotational slip. The Capture Plate prevents the crank bolt itself from backing out due to engine harmonics — the known OE weak point where the bolt gradually loosens over time. For high-powered builds MMX recommends pairing both for complete protection.

Does this require engine removal to install?

No. The BMW N55 S55 crank hub upgrade can be installed with the engine in situ. Access to the front of the engine is required, which typically involves removing the front bumper or radiator depending on the specific model and configuration. Professional installation is recommended given the precision required for dowel drilling.

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Description

MMX Billet 4-Pin Single-Piece Crank Hub Upgrade Kit for BMW N55 and S55 Engines

BMW N55 S55 crank hub upgrade from MMX Performance is the 4-pin variant of their proven single-piece crank hub kit, the version recommended for high-powered builds, modified engines, and any application where the unpinned hub cannot provide sufficient mechanical security against rotational slip. The documented failure mode on N55 and S55 engines is well established: the factory three-piece crank hub design relies on friction between plates to maintain timing, and under elevated power and torque, those friction plates can slip, advancing or retarding timing unpredictably and, in the worst case causing piston-to-valve contact with no warning. The MMX BMW N55 S55 crank hub replaces the factory assembly with a single-piece CNC-machined billet EN36 steel hub, case-hardened to 0.75mm for extreme strength, and adds four precision aerospace-machined dowel pins that mechanically lock the hub to the crankshaft, making rotational slip between the hub and crank physically impossible regardless of power level. To ensure precise dowel installation, the kit includes a complete jig set: a bolt-on drilling guide, location bolt, and high-speed drill bit. A new OE crank bolt is also included. For builds that need extra protection against crank bolt loosening from engine harmonics, the optional MMX Capture Plate is available to pair with this hub. Compatible with all N55 and S55 BMW models from the M2 and M135i through to the M3, M4, M4 CS, and M4 GTS.

Features

One-piece crank hub construction replaces the failure-prone factory three-piece assembly
Four precision aerospace-machined dowel pins mechanically lock the hub to the crankshaft, and rotational slip is physically impossible
CNC-machined from billet EN36 steel with 0.75mm case-hardening for extreme strength
Complete kit includes new OE crank bolt and full installation jig (drilling guide, location bolt, high-speed drill bit)
Recommended for builds over 700hp or any engine under elevated power and torque
Optional MMX Capture Plate available to secure crank bolt against harmonic loosening

Applications

BMW 135i: E82, E88 | 2010-2013
BMW 335i: E90, E91, E92, E93, F30, F31, F34 | 2010-2015
BMW 435i: F32, F33, F36 | 2013-2016
BMW 535i: F07, F10, F11 | 2011-2017
BMW 640i: F06, F12, F13 | 2011-2018
BMW 740i: F01, F02 | 2012-2015
BMW M135i: F20, F21 | 2012-2016
BMW M2: F87 | 2016-2018
BMW M2 Competition: F87 | 2018-2021
BMW M2 CS: F87 | 2020
BMW M235i: F22, F23 | 2014-2016
BMW M3: F80 | 2014-2018
BMW M4: F82, F83 | 2014-2020
BMW M4 CS: F82 | 2017
BMW M4 GTS: F82 | 2016
BMW X1 xDrive35i: E84 | 2013-2015
BMW X3 xDrive35i: F25 | 2011-2017
BMW X4 M40i: F26 | 2015-2018
BMW X4 xDrive35i: F26 | 2014-2018
BMW X5 sDrive35i: F15 | 2014-2018
BMW X5 xDrive35i: E70, F15 | 2011-2018
BMW X6 xDrive35i: E71, F16 | 2010-2019

Notes

Read about N55 and S55 crank hub failures here
Recommended for high-powered builds over 700hp. For stock to Stage 1 builds, the unpinned MMX single-piece crank hub is available.
Compatible with N55 and S55 engines only

Frequently Asked Questions

Why do N55 and S55 crank hubs fail, and what does the BMW N55 S55 crank hub upgrade fix? The factory N55 and S55 crank hub is a three-piece design that relies on friction between plates to hold the hub in correct timing alignment. Under elevated power and torque, that friction can be overcome, allowing the hub to slip rotationally on the crankshaft pulling ignition timing out of alignment and in the worst case causing piston-to-valve contact. The MMX BMW N55 S55 crank hub replaces the three-piece assembly with a single-piece billet EN36 steel hub pinned to the crankshaft with four dowel pins, making rotational slip physically impossible.
What is the difference between the 4-pin and the unpinned MMX BMW N55 S55 crank hub? The unpinned MMX single-piece hub eliminates the factory three-piece design and is suitable for stock and Stage 1 builds where power levels are not significantly elevated. The 4-pin version adds four aerospace-machined dowel pins that mechanically lock the hub to the crankshaft the correct choice for any modified engine, high-power build, or application where absolute certainty against slip is required. MMX recommends the 4-pin for builds over 700hp.
What is included in the BMW N55 S55 crank hub kit? The complete kit includes the billet EN36 steel single-piece hub, four precision dowel pins, a new OE crank bolt, and the full installation jig — a bolt-on drilling guide, location bolt, and high-speed drill bit to ensure accurate dowel placement during installation.
Do I also need the MMX Capture Plate? The Capture Plate and the BMW N55 S55 crank hub address two separate but related failure modes. The crank hub upgrade prevents hub-to-crank rotational slip. The Capture Plate prevents the crank bolt itself from backing out due to engine harmonics the known OE weak point where the bolt gradually loosens over time. For high-powered builds MMX recommends pairing both for complete protection.
Does this require engine removal to install? No. The BMW N55 S55 crank hub upgrade can be installed with the engine in situ. Access to the front of the engine is required, which typically involves removing the front bumper or radiator depending on the specific model and configuration. Professional installation is recommended given the precision required for dowel drilling.

About MMX Performance

MMX Performance is a UK-based specialist in performance parts for BMW and MINI vehicles, crafting high-quality upgrades that blend precision engineering, rigorous testing, and motorsport heritage. Driven by enthusiast culture, MMX designs its products in the UK and puts them through track validation to ensure durability, fitment accuracy, and on-road performance. Their catalog spans drivetrain components, spacers, hardware, and chassis enhancements, all tailored to elevate both the driving experience and visual appeal of BMW and MINI models.

Additional Information

The Bulletproof Automotive website contains many thousands of products purchased in multiple different currencies. All of the prices are entered manually and accurately at the time of entry. Due to the consistently fluctuating international exchange rates, at times prices may not be able to be honored at their original intended rate. We apologize for any inconvenience this may cause, unfortunately our website is unable to compensate dynamically for what can at times be volatile changes in the cost of items due to currency values fluctuating, changes in prices from suppliers, changes in shipping and import duties, and other factors. Rest assured that any order you place on line will be at zero risk to you in this area. If in the event your order cannot be fulfilled at the original intended website price we will offer you a 100% refund, no questions asked. We will continue to do our best to maintain updated prices and we will always continue to offer our price match guarantees as well to ensure our prices are always the best for you. In short, prices may change without notice. It is always advised to give us a call prior to placing your order online to confirm availability and to confirm current pricing.

Shipping Policy

Items that are in stock in the US, either at Bulletproof’s warehouse or at a supplier’s warehouse, are generally delivered within 7-10 days. Special order items from overseas take considerably longer. As a courtesy Bulletproof offers delivery estimates to our customers which take into consideration manufacturer availability and shipping schedule. These estimates represent our best guess based on previous orders from the manufacturer and do not in any way imply a guaranteed delivery window. Many manufacturers work in a “just in time” inventory system and often take 2-20+ weeks to produce an item once an order is submitted. All deliverable items are then sent to our Japanese warehouse. Bulletproof ships a minimum of one full ocean freight container every month from Japan, oftentimes more than one a month. Ocean freight takes an average of 4 weeks. Typically it breaks down to one week in Japan for paperwork and customs, two weeks by boat and one week in US customs/clearance. Due to the wide number of variables between manufacturer and shipping schedules, delivery estimates are simply just that – estimates. We attempt to estimate conservatively and we usually deliver faster than our estimates suggest. It is not Bulletproof’s policy to guarantee delivery time of any special order item, this is impossible for us to do. By ordering you acknowledge that there is no required delivery ETA and an order may not be canceled or altered due to manufacturing or shipping delays, all ETA’s are provided as a best guess only. Please review the full Terms & Conditions here.

BP Pricing Difference

We do pricing a little differently on our JDM brands and we believe in making things simple and clear. No hidden fees or surcharges. Every price you see includes the shipping cost to our office in Los Angeles, California and all the associated taxes/duties/fees for bringing the products into the US. The only shipping you ever pay is from our facility in the US to your location. Be wary of resellers that don’t include the cost of international shipping in their pricing on JDM parts. While we believe we’ll always have the lowest all-in price on JDM products, we offer a price match guarantee for all authentic parts purchased from authorized dealers as well. For many international customers, it’s much more affordable to ship from the USA than from Japan directly, as the air freight and ocean freight costs are typically much less. However, for customers looking to ship directly from Japan outside of North America, or domestically in Japan, we can provide pricing specifically for that scenario. Please do not hesitate to contact us with any pricing questions or concerns. Please email us at sales@bulletproofautomotive.com with any inquiries.

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MMX Billet 4-Pin Single-Piece Crank-Hub Upgrade Kit for BMW Vehicles (with N55 and S55 engines) [MMR20-1004/MMR20-1004FK]

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MMX Billet 4-Pin Single-Piece Crank Hub Upgrade Kit for BMW N55 and S55 Engines

Features

Applications

Notes

Frequently Asked Questions

About MMX Performance

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