ARP
ARP 201-6304 - BMW M10 Rod Bolt Kit

Unquestionably the most important fasteners in any engine are the connecting rod bolts, as they hold the key to the entire rotating assembly. A broken bolt will lead to catastrophic engine failure. As you can imagine, the most critical joint is where the connecting rod halves mate. The rod bolts must support the primary tension loads caused by each rotation (or cycle) of the crankshaft. When the crank rotates, the big end of the connecting rod essentially becomes oval-shaped and the rod bolts bend. As the crankshaft continues to rotate, the rod becomes round again. With alternating tension loads and cyclic bending of the bolts, it is very important to install fasteners that are able to exert a clamping force greater than the load imposed upon the joint (tension).

In addition to utilizing a rod bolt with sufficient strength to withstand the tremendous cyclical strains placed upon it, it is absolutely imperative that the bolts be properly tightened. The preferred method of monitoring the correct amount of tension is through use of a stretch gauge. This is far more accurate than using a torque wrench. Moreover, through subsequently checking the rod bolts length at teardowns, it is possible to determine if it has been stressed beyond safe limits and must be replaced.

For the most severe applications, in conjunction with aftermarket I-beam rods, ARP has developed the "Pro" Series bolts. These ultra heavy-duty rod bolts are made from a special material designed ARP2000. It has approximately 200% the fatigue life of 8740 chrome moly steel and has a tensile strength of 220,000 psi, and is capable of more than 12,000 lbs clamping force.