BMW M4 S55 Crank Hub Upgrade Kit | One-Piece & 4-Pin

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

We supply this one-piece 4-pin crank hub kit for BMW S55 engines in the F80 M3, F82 and F83 M4 and F87 M2 Competition and M2 CS. You recieve the hardened 4340 alloy steel hub with a genuine BMW M18 crankshaft stretch bolt, drilling fixture and drill bits.

The hub combines the sprockets in one piece to remove the separate internal friction interface in the factory assembly. Four locating pins connect the replacement hub to the crankshaft. Fitting requires precision drilling of the crankshaft and professional installation.

Vehicle fitment

The original N55 M2 and the S55 M2 Competition use different engines. If you are ordering for an N55 M2 please send your VIN through our contact form so we can check the application. The supplied bolt is listed for the applicable S55 installation.

What comes with the kit

• One-piece 4-pin crankshaft hub made from hardened 4340 alloy steel
• Genuine BMW M18 crankshaft stretch bolt for the applicable S55 installation
• Crankshaft drilling fixture
• Drill bits for the crankshaft modification

The optional front crankshaft seal guard is supplied only when selected above the Add to Cart button.

Why replace the original S55 crank hub?

The factory multi-piece hub relies on clamped friction surfaces to transmit drive from the crankshaft to the sprockets. If these parts move relative to each other the valve timing can shift. Symptoms can include timing fault codes and poor running. Greater movement can allow the pistons and valves to make contact.

Our integrated sprocket design removes one source of movement within the original assembly. The four pins provide mechanical location at the hub to crankshaft connection alongside the central bolt clamping force. The upgrade is intended to reduce crank hub slip risk on S55 builds including engines running increased power and torque. Accurate drilling and correct bolt tightening remain essential.

A slipped hub doesnt always mean the same repair. In an S55 M4 owner report a driver described being diagnosed with a bent valve after crank hub failure on a tuned 2016 F82. If your hub has already slipped have the engine checked for damage before fitting the replacement. Replacing the hub wont repair a bent valve or a damaged crankshaft mating surface.

The photos below show examples of crank hub related damage.

Drilling and fitting notes

We recommend a workshop experienced with BMW S55 timing systems and pinned crank hub installation. The drilling fixture helps position the holes but doesnt replace the engine timing and holding tools needed for the job.

Set and secure the engine timing according to the workshop procedure. Check that the fixture locates correctly on the crankshaft and stays fixed throughout drilling. Follow this kit's instructions for the drilling sequence, hole depth and cutting requirements. Dont angle the drill to compensate for a fixture that doesnt fit correctly.

Check the hole depth against the pin engagement specified for this hub. Pins that bottom out can prevent the hub seating fully even when the holes appear correctly aligned. Remove all swarf from the holes and surrounding engine areas before assembly. The hub must seat correctly without forcing misaligned pins.

Use the specified holding arrangement for final tightening. Dont assume the timing setting tools can carry the central bolt tightening load. Complete the prescribed manual rotation and timing checks before starting the engine.

Central bolt tightening reference

S55 M18 crankshaft hub bolt: 100 Nm followed by 270°.

Verify this reference against the current BMW workshop procedure and the instructions for the supplied hub and bolt. Use a new correct specification stretch bolt and follow the required thread preparation and tightening sequence. Any accessory fasteners need the settings supplied for that particular component.

Optional front crankshaft seal guard

The front crankshaft seal guard is available seperately as a selected extra. Its intended to help prevent a damaged auxiliary belt being drawn behind the crank pulley and through the front crankshaft seal. Check the belt, tensioner and any nearby oil leaks during the job. The guard doesnt replace those repairs or lock the central crankshaft bolt.