Rotor Bolt Usage

[IanDMacDonald]

I installed 1/2" spacers between the rotors and the wheel rims on each side, mounting aftermarket rotors. I was able to install the rotor bolts with more than enough thread. However, I assume that Yamaha used the length of bolts they did for a specified reason. So, should I be using longer bolts, and what exactly should I be looking for with those bolts? My buddy said they are a special bolt, and should not be swapped with anything other than the exact same bolt.

[DiverRay]

Any grade 8 bolt should work. and yes, going out 1/2", or about 12mm, would call for longer bolts. Main thing is make sure there is no movement between the bolt and the rotor. with all 6 bolts in loose, the rotor should NOT turn much, if at all.

[fredintoon]

- - - My buddy said they are a special bolt, and should not be swapped with anything other than the exact same bolt.

Hi Ian,
betcha it's the stock fasteners' shallow heads that lead to your buddy's concern.
Mr Stupid's Allen head + spring washer substitution for sure didn't work too well.

[TopCatGr58]

Hey Ian,

How wide are the spacers? Are they just cylinders? Do you have access to any plate aluminum or steel material in the same 1/2" thickness. Cutting some arcs to cover 2 bolt holes between the rotor/hub would provide more stability of the rotor against the hub vs. just the narrow spacer cylinders. The braking action will put torsional stress on the bolts...the longer the gap between the rotor and hub, the more lateral stress on the side of the bolts. With the thick arcs of spacer material, it will help reduce flexing action of the rotor against the hub via the long bolts.

I suggested the arcs vs. trying to make a complete spacer DISC for both weight, cost, and complexity. JAT!

T.C.

[IanDMacDonald]

Hey TC-

Yes, I do have access to any type of plate stock in aluminum, galvanized, and stainless, along with a lathe, band saw, and Bridgeport. But, the spacers are made already, so I don't want to throw good work and material to waste. I just bought some 40mm bolts, vs. the stock 31mm bolts. I may also try 45 mm one's if I find an Ace open nearby tomorrow. Funny thing, I stopped by a HUGE Ace on the way back from getting my tires mounted, and when I walked inside, I realized it was more a lumber store, than hardware. Short story, they did not stock metric fasteners. Did not ask, did not care to ask. Just kinda weird.

Fred- Yes, my buddy is a machinist. The second he saw that head on the bolt, he said I should not even think about anything else other than that same bolt, and rattled off the tension specs, etc. on it.

[TopCatGr58]

Hey again,

Well, it sounds like your spacers are possibly a bit more ROBUST than just simple washer stacks or cylinder tubes. If so, then being wider should help spread the stress along the surface of the rotor and not just concentrated on the bolt head alone.

T.C.

[Rasputin]

Grade 8 bolts have a lower shear strength than a grade 5 bolt does. Better be sure to do some research on this. While a grade 8 does have superior tensile strength, to a grade 5 bolt, the shear point is lower. JAT before you trust your hide to a brake bolt that may fail.

[crazy steve]

The original rotor bolts aren't grade 8; they have those special 'tall' heads on them so the OEM locking tabs won't protrude above them.

I used button-head stainless steel with a liberal dab of Loctite under the bolt heads. Make sure you torque the bolts.

The one thing to be careful about is if your spacers don't extend the center-hub shoulder that the OEM rotors (or your aftermarket ones) locate on, this will allow stress to be transmitted to the bolts and may not 'center' the rotors properly. Check for runout once the rotors are installed....