Mattbastard had the same issue with his rocker cover bolts. I seem to remember there was a good discussion on various possible causes:

https://www.hdforums.com/forum/engin...-8-my-***.html

 

Maybe when talking about hardware store ss hardware...ARP stainless bolts are 180,000lbs... stronger than grade 8 which is 150,000 lbs...


https://arp-bolts.com/kits/bulk-list...=*&Set1_page=1

 

The factory bolts for the rocker box are not grade 8. Just a plain grade 5. I know, I snapped one on the Sportster once. Had to pull the head. Last time I've used a torque wrench on a Harley outside of a head bolt.

The stainless bolt for the adjuster would be just fine, in my opinion.

 

ARP bolts are the bomb-diggity, but they don’t come in fully threaded, which is what I need for axle adjusters. They also don’t come in hex head or socket head. I think the choice is six or twelve point.
They are also very pricey, compared to grade eight they cost 4 or 5 times more.

 

delete double post.

 

Loose screws or bolts come under a different kind of stress and are just as liable to snap as one that has been over-tightened.

 

YES!!! **** fasteners... Just a large batch of mismarked bolts from China.

 

Timely discussion, this is something else to add to the list of things to improve when my engine goes back together.

 

As the grade goes up the tensile strength is supposed to go up. As many have experienced the higher grades are also more brittle and may fail by breaking. AN (Army Navy) mil-spec fasteners are designing to bend, not break. The military doesn't want parts falling off of airplanes and tanks.

 

Make sure you're torquing the bolt to the correct spec. Grade 8, grade 5, grade godzilla, doesn't matter if you have enough muscle and leverage. Most guys could break any 1/4" bolt alive with a decent breaker bar.

carl