ARP Main Stud Kit - M240i/M340i/M440i (B58)

ARP studs for the main crankshaft bearings on all B58 engines (B58A, B58C, B58D) used in M240i, 340i, 440i, 540i, and M40i models. Replaces BMW part numbers 11128644674 and 11127613127.

We use the ARP Main Stud Kit on every engine we build and race because in heavy use applications, stock parts don't get the job done. Simply stated, there's not a better stud setup on the market today.

For starters, ARP Main Stud Kits use a premium grade 8740 alloy that is rated far superior to even aircraft-quality parts. Then, each stud is placed vertically in special racks and precisely heat-treated to 200,000 psi. This procedure ensures complete heat penetration, and the results are far superior to those lesser quality studs from other manufacturers who just dump pieces in a basket and hope for the best.

Following the heat treatment, each ARP Main Stud is centerless ground to make it as close to perfectly concentric as possible. This procedure involves about ten very slight cuts and results in an exceptionally straight part. It's important to note that lesser quality studs are not even centerless ground - the material is thread rolled in bar stock form, and usually before heat treating, when the material is easier to machine.

ARP Main Stud Kits are thread rolled after heat-treating, which gives them about 1000% (that's ten times) better fatigue strength than those studs that are threaded prior to heat treatment (a very common industry practice). It costs more to do it this way, because it's tough on tooling, but the results are well worth the extra effort.