There's nothing wrong with the old factory bolts on the bike now, other than I've taken them out while doing some work on the bike. While I can clean them up and use them again, I went to the local bolt store and picked up some black ones with the allen instead of the stupid torx. They're grade 8, but the head is a bit smaller, which I like, but have to make sure they're safe.

Any legit thoughts?

 

I don't know of any reason why they wouldn't be OK. I would use them.

 

Id say no. The smaller one has less line of strength. Less meat. Id just get OEM one's. Not worth the risk.

 

the bigger bolt heads have more clamp force against the rotor surface .

 

Using a grade 8 bolt is a good choice however the specific bolt you have pictured does not have the appropriate size head to provide sufficient clamping force. I suggest if you want to use an Allen head bolt doing a search for one with a larger head. Find a Fastenal store local to you and bring or Torxhead bolt with you for a replacement Allenhead bolt.
Bob

 

I wouldn't recommend it! The grade 8 bolts that are black are unplated black oxide that will rust very quickly. If you want to replace them (which I wouldn't blame you for, torx bolts are tough to turn at high torque) Try the gold hex heads (Zinc-plated). Even clearcoating the black oxide bolts is not enough to prevent them from rusting.

 

^^What he said^^

 

Biggest concern I have is the black oxide fasteners will rust and corrode in the aluminum wheel. Stay with the factory plated stuff which has been corrosion tested. The balck oxide stuf will begin to rust almost as soon as they get wet.

 

The engineering response is no.

What you are dealing with are technically screws, not bolts. Bolts have an un-threaded part of the shank. Screws are threaded all the way to the head (generally speaking, but both have odd cases.)

As several people mentioned, the head is incorrect. The black screw in the photo is a shear type fastener. This means that it is designed for cross-wise strength, it isn't intended for applications that rely on the "pull" of the fastener lengthwise.

The HD fastener appears to have the head of a tension type fastener, which is rated for lengthwise pull. However, screws are typically not used for tension applications. This is also odd because a brake rotor seems to be a shear application.

The comments about unplated metal are good too.

Finally, fastener strength is not as simple as a grade #. Yes, grade 8 is stronger than grade 5. But, in terms of metal strength, when strength increases, elasticity decreases. Meaning, the stronger the metal, the more brittle it becomes. Grade 8 is not always "better, is is just harder. Some applications rely on a fastener's ability to deform prior to catastrophic failure.

 

I would rather reuse the old bolts than use those...