flattened rotor screws - need advice

[johnny1990]

hey I just took my rotor crews out of my front hub but they where really tight coming all the way out, when i got them out i realised the thread had been flattened (picture below should give you some what of an idea what I'm talking about).

The brakes I'm using are hope m4 with a 8" rotor with a chris king hub(I wouldn't think something like this would happen with a quality hub !). I haven't checked the rear screws yet to see if they have done the same thing, both brakes have been on for about 1 month and these screws are stainless steel.

Would titanium screws reslove this problem and what would be the cause, i went to my local bike shop but they are both prety hopeless and someone else on here may have had the same problem.

ps. sorry for the crappy quality picture.
http://i33.tinypic.com/mcw5tz.jpg

[rush]

The likelihood is that it is just the bolt that is threaded (flattened). Looking at the bolt, only the top half is gone, so it follows that the hub thread is ok.

It happens when the thread on the bolt crosses over the thread you are screwing into or out of.

I would grab some more bolts from a bike shop or a hardware store (make sure they are exactly the right size, bike shop would be better), then screw your rotor back on.

Do this very very carefully, and very very slowly. If you feel any roughness or tightness, check the bolt for any loose shavings of metal, or any extra bright/shiny bits where the thread might have crossed.

Also, be sure to check your hub before you do this. If the threads on your hub are fucked, then you should not do anything except take them to be helicoiled or re-threaded.

[john trials]

The hub is made of aluminum, then anodized (which is a fairly hard coating, but it is thin). The screw threads are stronger than the aluminum (if it is a decent fastener). If the steel screw threads are messed up, I'd bet that the threads in the hub are messed up too.

Are all of the screw threads worn out like the one on the right?

Check the threads on the hub. If the anodized surface is worn away (cut up by the screws), I'd try carefully chasing the threads with the correct tap to clean out the hub threads. Hopefully they are not so bad that the hub needs to be helicoiled (threaded inserts to replace the ruined threads in the hub).

These screws should only be tightened to about 55 in-lbs...this is not very tight. These screws are stressed in shear, so they don't need to be super tight. They may have been over tightened in the past and ruined the threads in the hub.

[johnny1990]

when I tighten the screws I only use the avid torx wrench that comes with the brake stepup's which would be only 3" long so I don't think that over tightening is the problem,4 of the front bolts have been damnaged like this and they were all new.

I checked the thead on the hub and that was fine(the anodizing is still on the thread and no metal shing/fileings) and tried the good screw from the picture and it threaded in like a dream. The rear screws are fine also.

The rotor has come loose a few times but tighten it staight away when I notice movement. I'm thinking I must take some force to damage the thread like this, so the braking force must be the cause but I don't see how it could flatten the thread.

[rush]

I dont think braking force has much to do with it.

I would say you had shit rotor bolts.

[johnny1990]

ok ill get me some tryall titanium rotor bolts then, would anybody in australia stock them or are there any other brand that do titanium ?

[thetart20]

The problem is this: If you keep the other 5 bolts tight and take one out, the threads will run against the rotor. The rotor is MUCH tougher than a bolt so it screws up the threads, that's why it was so hard to get out (the one with all the threads screwed up) and there is no damage to the hub.

Fitting a rotor: Always tighten the bolts down gently, then back off 1/8th turn, twist the rotor in the braking direction, then tighten down in 1, 3, 5, 2, 6, 4 pattern. The ensures the rotor runs true and round.

Undoing: Loosen all the bolts off a teeny bit before unscrewing any one bolt all the way.

Cheers
Adam

[goose]

dude, before you buy spensive bolts... they're a standard thread eh... just M5x0.8mm. I'd check to be really really sure that the threads in the hub are fine. Any local hardware store should have some bolts with an M5 thread.

[john trials]

The damage to the screw on the left (up near the head) looks like it happened when the screws came loose, and the disc shifted. That shouldn't ruin the threads that are down in the hub.

Titanium screws would be a waste of money in my opinion. Steel performs just fine. The screws you used may have been poor quality. It looks like you just used what you had lying around (the length of the screws are different, and the heads are different). Just buy a quality set of steel screws at your LBS. You should be fine.

Luckily your hub is not damaged.

[johnny1990]

I forgot to add that the screw on the left in the picture works fine it was just for comparion to to damaged rotor.

When I tighten the screws I just tighten 2 opposite ones first to make sure its centred and then tighten the other 4, I'll try what you said it makes a lot of sence.

Thanks for all your advice anyways.

[rndm*dv8n]

thetart20 had an excellent point. Where the thread is damaged is where it would have been in contact with the rotor, not the hub.

So either the thread was damaged when your rotor shifted while you were riding. Or, after the rotor shifted, the thread got stripped on the rotor while you were unscrewing the bolts (consistent with seeming to be really tight and 360degrees of stripping).

Either way, the problem is the rotor/bolt interface not the quality of the bolt or hub.

I've had a similar problem, the rotor shifting, the trouble is when the braking direction is both front and back. New rotor bolts with a liberal application of loctite solved my problem, it was a real bitch, however, to get the rotor off.

hm, I just noticed something on the right side bolt in the pic: it tapers up from the thread to the bottom of the bolt head, whereas the left hand bolt doesn't. The taper or wedge shape might aid in keeping the rotor in place, whereas with the bolt on the left this is entirely up the bolt thread... or maybe I'm reading too much into an e-pic?

[Elan]

your hub is toast

[Rodmunch]

The problem is this: If you keep the other 5 bolts tight and take one out, the threads will run against the rotor. The rotor is MUCH tougher than a bolt so it screws up the threads, that's why it was so hard to get out (the one with all the threads screwed up) and there is no damage to the hub.

I agree with this. It's all user error. The idea is to loosen ALL the bolts BEFORE taking any out. You probably took out one bolt at a time which caused the damage. Just get some replacement steel screws and be done with it.

[Cypher Components]

If the hub threads are really fine, then it's just rotor clearance hole misalignment when you removed the screw. Stainless bolts aren't that strong. I would go to mcmaster.com and order Grade 8 M4X0.8 steel bolts if you want strength. Or get the high end Stainless ones, not the cheaper stainless ones. And then do as they say above, loosen them all just enought to have the rotor unstuck before you take one out.

If the hub is toast, you can step up to the next size bolt, just re-drill and tap the holes, and drill a slightly large hole in the rotors. Might want to do that on a drill press or a mill. . .

[rush]

thetart20 had an excellent point. Where the thread is damaged is where it would have been in contact with the rotor, not the hub.

So either the thread was damaged when your rotor shifted while you were riding. Or, after the rotor shifted, the thread got stripped on the rotor while you were unscrewing the bolts (consistent with seeming to be really tight and 360degrees of stripping).

Either way, the problem is the rotor/bolt interface not the quality of the bolt or hub.

I've had a similar problem, the rotor shifting, the trouble is when the braking direction is both front and back. New rotor bolts with a liberal application of loctite solved my problem, it was a real bitch, however, to get the rotor off.

hm, I just noticed something on the right side bolt in the pic: it tapers up from the thread to the bottom of the bolt head, whereas the left hand bolt doesn't. The taper or wedge shape might aid in keeping the rotor in place, whereas with the bolt on the left this is entirely up the bolt thread... or maybe I'm reading too much into an e-pic?

Just FYI, he is only talking about the bolt on the right hand side in the pic. The other was just for comparison i believe..

[thetart20]

order Grade 8 M4X0.8 steel bolts if you want strength
M5x0.8 for disc rotor bolts! (Just looks like a typo as I understand you are well-up on this sort of stuff, but just wanted to make sure the thread starter doesn't spend ages looking for bolts of that size!)