Replacement shock bolts
#1
03-13-2014, 12:06 PM
Replacement shock bolts
Need a bit of help guys. Picked up a side mount license plate kit for the bike. Only problem is where it mounts on the left shock the bolt is half an inch too short. Checked with harley and they don't make a bolt any longer. Now I need a solid replacement and I'm not really sure what would be good. Been trying to find a grade 8 bolt 2 and 1/2 inches with 13 thread. Been to the local shops and they look at me like I'm speaking gibberish when I ask for something similar or recommendations. Been digging on bolt depot.com and they have some stainless 18.8 grade socket caps. Not sure it'd work though. I just need two of them that way both sides of the bike match. 
#2
03-13-2014, 12:22 PM
You're right that it's a 1/2x13 thread.
I wouldn't use the stainless steel bolts unless you can find one rated at 180-200ksi. Normal stainless steel fasteners from the hardware store aren't heat treated to this strength.
A grade 5 bolt will work fine for the shock bolt application. I'm not sure what stores you have locally, but the Lowe's and Home Depot here in Savannah have 2 1/2" long grade 5 bolts.
The difference between grade 5 and grade 8 is the strength, but the stronger the fastener, the more brittle it is unless you get special materials (expensive.)
A grade 5 bolt will handle far more stress than you can apply in this application.
I wouldn't use the stainless steel bolts unless you can find one rated at 180-200ksi. Normal stainless steel fasteners from the hardware store aren't heat treated to this strength.
A grade 5 bolt will work fine for the shock bolt application. I'm not sure what stores you have locally, but the Lowe's and Home Depot here in Savannah have 2 1/2" long grade 5 bolts.
The difference between grade 5 and grade 8 is the strength, but the stronger the fastener, the more brittle it is unless you get special materials (expensive.)
A grade 5 bolt will handle far more stress than you can apply in this application.
#3
03-13-2014, 12:29 PM
#7
03-13-2014, 12:53 PM
I doubt you'll ever have a problem it's just that ratings for SS fasteners have a wide range in their strength rating and you never know what you'll get. The minimum requirement for standard 1/2" 18-8 SS fasteners is half of that of a grade 5 bolt's minimum (although they rate them as "typically" much higher.) They still rate much higher than the load a 700lb bike with 500lbs of rider/cargo can apply. I'm just sketchy about structural joints and fastener strength.
Trending Topics
#9
03-13-2014, 06:06 PM
Just for perspective. The minimum tensile strength for all three types are:
SS = 100,000 lbs/square inch
Grade 5 = 120,000 lbs/square inch
Grade 8 = 150,000 lbs/square inch
The shear area of a 1/2" fastener is 0.19625"
So, the force to shear each 1/2" bolt is 0.19625 x the tensile strength of the material.
SS = 19,625 lbs
Gr 5 = 23,550 lbs
Gr 8 = 29,437.5 lbs
Some bending forces will apply, but I'd need HD design data. However, the actual failure for one of these bolts would be close to these numbers. That's just for one shock. No way will any of us apply that kind of load. I doubt Evil Knievel would exceed these loads.
The real test is fatigue life (retention of their strength properties over time.) Both heat treated metals have much better fatigue properties than the SS. That's why I wouldn't use SS, but wouldn't hesitate to use grade 5 or 8.
Keep in mind, this applies to fasteners under shear loads (perpendicular force.) fasteners under tensile load (lengthwise force) require several additional considerations.
Last edited by SLV; 03-13-2014 at 06:11 PM.
