One of the hidden weak points to the S54 engine in the E46 M3, MZ3, Z4M is the mounting bolts for the cam sprockets. The original bolts are known for working themselves loose, which puts more stress on the the shank portion, and they have been known to snap straight off. It's a .50 cent part that can lead to thousands of dollars in repairs. BMW re-issued the bolts with a stronger material and experts recommend using Loctite or thread-fastener with the new bolts.
There are two bolts to be aware of -
- 07129905536, fillister-head M6x16 screw (fillister = Torx). This mounts the sprocket to the camshaft. These are the S54 bolt failures and these must be replaced with the new bolt design.
- 07119913589, M6x25 hex bolt. These standard hex bolts mount the "hub" to the sprocket. The hub is on the outside of the sprocket (the exhaust has two tabs sticking out). These bolts are not known for failure but the originals should not be re-used at this point.
There are other issues to be aware of in this area - broken tabs on the exhaust hub, worn seals in the VANOS unit, etc. S54 VANOS replacement and overhaul should be done as part of a preventative maintenance plan every 70,000-80,000 miles. This kit includes 12 of each bolt for a full replacement.
BMW Fitments:3 Series
E46 (01-06) > M3Z Series
Z3 (01-02) > M Coupe
Z3 (01-02) > M RoadsterZ Series
E85 / E86 (06-08) > Z4 M