Today i swapped out the stock front brake rotor bolts for some M6 x 1.0 x 16mm grade 10.9 black oxide coated bolts. 10.9 is listed as the same as grade 8.

In the picture you'll notice the hex button head is much smaller on the new black oxide bolt, but i'm thinking that shouldn't be a factor because the bolts only recieve shear loads from the rotors, and i'm still using a good grade, M6 bolt, just like the stocker.

Can any engineers weigh in on this: Eric? Skokie?

Thanks!
James

P.S. In addition there is a weight savings of 1.4oz... I don't care about the weight savings, just thought i would mention it...

 

Another pic

 

Where as you are correct that the bolts are primarily in shear there is lateral load on the bolt heads due to the fact that the caliper pistons do not engage at exactly the same time or the same pressure amount for a fraction of a second but once equal clamping force is applied by the Pistons on both sides of the rotor the forces should equal out but it is that split second of lateral load x thousands of brake applications that can cause metal fatigue or work hardening

a grade 8.8 bolt equivalent should be adequate but corrosion induced cracking could be a concern with a black oxide coated bolt but it could be treated with a non hardening film-forming corrosion inhibitor as manufactured by CRC with their sp400

Also without knowing the purchase area Delta between the stock bolt head and the alternative bolts head and the head thickness difference or the actual loads being applied it would be difficult to know for sure but careful and consistent monitoring of such a critical component is essential as well as its pretensioning force often referred to as torque or tightness and that measure may be different between the grades of bolts in relation to bolt clamping head area

 

Ok... The good news is the bike doesn't see inclimate weather.

Would you like a picture of the bolt heads (taken from the side) showing stock bolt va new bolt?

Update: picture attached

James

 

More updates:

Stock bolt head diameter: 13.5ishmm
New black bolt head diameter: 10.5mm

I can get a flanged button head bolt (in black) with a head diameter of 13.5mm to match the stocker... Is that what you would recommend?

James

 

If you look what torque value honda recommend for this M6 disc bolt, you will see it is far more than common values for M6 bolts described in standards. It seems that some deformation of the bolt after tightening is counted into. Second fact is, manual recommends new bolts for reinstallation.

Personally I rather bought new oem ones, despite the fact for calipers I use standard hardened bolts from hardware store.

 

James,

For such a critical application I wouldn't use anything other than the factory spec item.

I have replaced almost every bolt on my bike , however discs bolts are all standard.

I wouldn't feel comfortable with anything else as I rely heavily on my brakes, especially during moments of insanity either escaping or catching my mates.

Please go back to standard.

 

If you are looking for black bolts, do what I did and paint the heads of the stock fasteners. Only had one chip the paint on installation. Touch up was easy.

 

The amount of material above the diameter of the oem bolt compared to the alternative bolt is what I was referring to not just its diameter.

I would stay with the oem bolts, replacement may not be necessary though prescribed by the manual just as it is with the oem caliper to fork mounting bolts.

 

The clamping surface is greatly reduced.

 

I know... I know.... Sigh

Its raining here all week so i've been polishing the stock bolts before putting them back in. I'm not a big fan of paint...


Anyone know of anybody on the net who does black oxide coating? I could send my bolts in this winter

Or better yet maybe Honda made a bike with black bolts stock... I could get some of those

James

 

Ceramic coating would be an option...Use one of the protective / lubrication ones in a dark color
Cerakote Coatings: C-110Q Micro Slick Dry Film Coating

 

Without my clicking the link or researching this coating in any way, how would that affect properly torquing the bolt (wrt any lubricating properties of the coating)?

 

For this application, none at all.

 

Alright, I clicked the link and, as this coating is claimed to reduce friction, how can that not affect the stretch of the fastener when torqued to spec? Unless, of course, the spec is modified for the coating.

 

Because in this application it's not critical
And like all fasteners subject to vibration and required to not come loose, a anaerobic thread lock in medium strength is a great idea.

TQ to factory specs and use a drop of something like Loctite 242
Loctite Threadlocker Blue 242 from Loctite Adhesives

Yes, as an engineering standpoint, lubed or dry threaded fastener for TQ needs makes a difference. As you plan on tossing all that engineered data out the window with stainless steel fasteners (if you could find them) stressing out on tq speck for a lubed vs dry fastener is a bit much.

If you have an inspected, calibrated, accurate TQ wrench and want / know how to use it correctly and reallllllly want to know the adjusted tq spec to get it in the speced stretch zone, if you're using a known quantity fastener (so not OEM as we have no data on them) I can help you get to a specific number that is reasonable accurate.... However as about a million and 7 people a day are using a rusty craftsman ratchet after having consumed some quantity of cheap beer to "torque" those same suspension bolts and see no observed catastrophic event.. Id say you'll be fine to wing it. LOL

 

I'm just jumping on the stress-out bandwagon cause James wants to sub a different bolt for his rotors.

 

Lol.... I KNEW this thread would cause hypertension!

It is great to be friends with so many caring people on this forum. Never before have I been part of such a caring community (except for maybe the air cooled VW community).

Eric: this should be your new sig: Id say you'll be fine to wing it. LOL (you'll sell more flywheels with this sig guaranteed!!)

LOL


James