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When automakers specify engine mount requirements, harmonic damping bolts are only used to mount the balancer, so they usually have a flat hex head. But in the high performance world, the balancer bolts are under severe stress as the engine must be cranked by hand to set timing, adjust valve clearance, etc. This often results in the head of the bolt being “rounded off” due to heavy use – sometimes to the point that it is almost impossible to rotate it.
Worn damper hex bolts compared to new ARP bolts. ARP damper bolts are supplied with a large 1/4″ washer for better clamping load distribution and an ARP Ultra-Torque Fastener Lubricant package for proper preload.
That’s why the ARP engineering team focused their efforts on developing the “Ultimate” balance bolt. Features a high nod 12 for easy access to deep sockets for increased contact area. With this design, there is no need to worry about the rounding of the bolt head, whether for repeated use or high torque loads. The company also offers a replacement damper bolt designed to accept a standard 1/2″ square drive, allowing you to use a large ratchet or chopper arm to crank the engine. On the outside, the bolt is still a large hex. Best of all, the ARP balance bolt has a 1/4″ thick large diameter washer to optimize clamp load distribution.
ARP offers many options for many applications, including large hex head bolts or deep 12 point heads machined to hold a 1/2″ square drive. Both designs support constant motor rotation better than standard bolt-on designs.
ARP balance bolts are manufactured from a high quality nickel chromium molybdenum alloy and precision heat treated to a tensile strength rating of 190,000 psi, much stronger than OEM equipment. Also, ARP damper bolts are reusable, while most factory mounts are torque rated and should never be reused.
Another important feature of ARP balance bolts is that the threads are rolled after a heat treatment process rather than the more common threading. The threads are formed according to SAE AS8879D specifications for optimum engagement with the crank head. The combination of all these properties provides ten times the fatigue life of conventional fasteners. Providing high RPM safety and easy engine maintenance, ARP balance bolts are a worthwhile investment for any rider.
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