For S50B30 engines, the Vanos piston bearings have axial play. This play shouldn’t be there. The camshaft engages this play back and forth as the cams compress and decompress the valve springs. At certain RPM ranges these movements can resonate and you get a rattle. The M3, due to its aggressive cams (especially if uprated) is more susceptible to getting the resonance and rattle.

Of course all the pistons have loose bearings and it’s best to remove this on all the cars. Even if a car is not experiencing a rattle, the resonance and rattle can develop at any time.

The Vanos Rattle Repair kit includes two sets of replacement bearing rings and outer washers, which can be fitted to significantly reduce this play, thus stopping rattle and avoiding rattle becoming a future problem.

For fitting, special tool (part number BS094) is required – available to hire (see parts listings).