I wanted to provide you with an update regarding the SPL service bulletin. The bulletin addresses issues with their previous bolt style, which tended to gall out due to insufficient torque, leading to infrequent but severe failures. As a precautionary measure, SPL has issued a service bulletin advising users to remove the bolts and inspect the threads for galling. If the bolts were torqued under 110 pounds, replacement is recommended due to fatigue.
Following the service bulletin guidelines, I removed and replaced my bolts with the new, albeit more expensive, stud design. However, the installation proved challenging (requiring 180LB of torque), and I'm uneasy about having a nut on both ends.
Considering reverting to the old bolt design, I encountered a flaw: the bolts were only 4 inches long, and the threads were damaged by the jam nuts upon removal. To address this, a friend suggested a solution: using 4.5-inch-long, highest-grade ASTM A574 bolts with the addition of a spacer for increased articulation (see arrow). Use the same number of spacers you had before above the bearing. A robust Grade 8 nylon nut was chosen for one end, and the entire thread was treated with copper antiseize. Torquing to 124 pounds (lubricated torque) and marking with a paint marker completed the process. Routine checks, including inspecting the marker, are now part of my pre-track weekend routine.
Black-Oxide Alloy Steel Socket Head Screw
5/8"-18 Thread Size, 4-1/2" Long ASTM A574 (equivalent to 12.9 grade)
https://www.mcmaster.com/91251A489/
High-Strength Steel Nylon-Insert Locknut
Grade 8, Zinc Yellow-Chromate Plated, 5/8"-18 Thread Size
https://www.mcmaster.com/97135A275/
Service Bulletin:
https://www.splparts.com/tsb-2301/
SPL Studs = $73 shipped (I don't love this design)
My solution = $28 shipped, you can use these for other SPL arms and preventative every 3 track season. (proven SPL design, just longer and stronger bolts)
*This is based on my research and experience with hardware. I'm not responsible for damage if you follow my method. These ASTM A574 are stronger than SPL's Grade 8 original style bolts, and it's longer for more thread count.