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Talk => Speaking Of Bikes... => Topic started by: Nick Calne on April 05, 2020, 06:27:19 PM

Title: A question about your nuts...
Post by: Nick Calne on April 05, 2020, 06:27:19 PM
Well bolts actually... but now I have your attention...

Why on disc brake rotors do they install Allen head bolts to fix to the hub?

It seems every time a rotor has to come off the bolts are seized on with lock tite and brake heat. Trying to get the bolt out involves the risk of rounding the head. At least one of those tiny little surfaces gets rounded. Today it was 5 out of 12. Which, keeping on the nuts theme, was a bollock.

Why don't they use normal bolts you can get off with a socket?
Title: Re: A question about your nuts...
Post by: London_Phil on April 05, 2020, 07:38:45 PM
You need heat on the bolt to help break down the loctite, but even then its hit and miss.
I did my Steamer years ago, and used a heat gun to get the bolts hot, but I made sure I hade a top quality Allen hex on a socket, so I could put downward pressure whilst turning. (Wheel on floor, set between  some 4x2's.)
Still ruined a few, but at least they were out.
I think they are like they are for clearance, and aesthetics too.
Its all a labour of love, so keep calm, and carry on.....
Title: Re: A question about your nuts...
Post by: Timbox2 on April 05, 2020, 08:46:54 PM
I think KTM realises this which is why they use twin drive heads, torx and hex head in one, nifty
Title: Re: A question about your nuts...
Post by: London_Phil on April 05, 2020, 10:41:16 PM
We used to have those in Kodak Copiers from 20 plus hears ago... Damn good idea too
Title: Re: A question about your nuts...
Post by: Nick Calne on April 06, 2020, 07:20:58 PM
Thanks for the responses guys. So there would be nothing wrong with using a standard hex bolt then? Other than it might look a bit gash.

I think the one I have in mind is called a washer hex head.
Title: Re: A question about your nuts...
Post by: Timbox2 on April 07, 2020, 07:35:35 PM
Quote from: Nick Calne on April 06, 2020, 07:20:58 PM
Thanks for the responses guys. So there would be nothing wrong with using a standard hex bolt then? Other than it might look a bit gash.

I think the one I have in mind is called a washer hex head.

Flanged Hex is what I would call them: Similar to this?  With a dab of Loctite 232 (Medium)

(https://i.ebayimg.com/images/g/2jYAAOSwYS5clnn8/s-l640.jpg)
Title: Re: A question about your nuts...
Post by: Nick Calne on April 08, 2020, 09:05:06 AM
That's them. I ordered some from Ebay.
Title: Re: A question about your nuts...
Post by: Sin_Tiger on January 16, 2021, 07:05:37 PM
I know this is an old thread but I only just spotted it and feel it's sufficiently important to refresh it.

Common disc bolts are close tolerance shouldered bolts. to ensure the torque load applied to the brake disc is transmitted evenly across all of them to the hub and the disc should not move.

The ones pictured are flanged, serrated machine screws, do NOT use those.

1) They will not locate the disc sufficiently accurately which will allow radial movement and possibly a disc coming loose.
2) The torque load applied to the disc will be transmitted through the thread and if there is any movement at all the thread will have a cutting effect like a chisel.
3) The shear load area is greatly reduced, effectively the root diameter of the thread compared to a shouldered & fitted bolt.
4) The serrations will chew into the the spot faced contact areas on the disc, so even if you change back to standard bolts the disc will now be compromised.
5) Those will be a lot heavier than the proper bolts and weight can vary a lot with that type compared to the proper bolts.

If you want to give yourself the best chance of getting a stubborn bolt out without damage. Use the best quality hex bit you can find, I keep a really expensive one that is used for no other purpose. Warm them up as already suggested just before you start removal. Give the bit a solid whack to ensure the bit is well seated, any remaining debris is compressed and it also helps to disturb the locking compound hold. Use a bit with an extension and a T bar on the end so that you can comfortably apply force evenly without uneven angular effect.

NEVER use an Allen Key, NEVER use a Ball Head  :cp
Title: Re: A question about your nuts...
Post by: Nick Calne on January 17, 2021, 11:06:09 PM
Too late now..... :nap
Title: Re: A question about your nuts...
Post by: Sin_Tiger on January 18, 2021, 05:02:27 PM
If you get a really chewed one that just isn't going play and has you looking for a grinder, there is another option.

Weld a mild steel nut onto it. I think an M12 is about right, drill the thread out of it to give you a fighting chance of getting a decent weld and so that it fits as close to the outer diameter of the disc bolt flange. Grind the chrome off the disc bolt (you won't have a chance of getting a decent weld otherwise) but don't take any more metal off than you absolutely have to, just until you get proper sparks.

Degrease the bolt head and nut but cover your disc if you hope to reuse it, either proper weld anti spray the disc or a light smear of copper grease on the disc will also work. Place the nut over the disc bolt and plug weld inside the nut onto the disc bolt. I've used stick on larger items but there's too much risk of slag getting in the way of a good weld so MIG is the best option, you can use TIG but if you're that skilled you've probably used this technique before. The heat will help soften the thread lock, you want to wait long enough for it to cool to the point where it's not going to chew but not long enough for the heat to dissipate into the hub, before you try to remove it.

I've only had to resort to this once many years ago but have frequently used this technique to remove sheared studs, chewed bolts, seized clevis pins and even a knackered diesel injector on one occasion.
Title: Re: A question about your nuts...
Post by: ghulst on January 18, 2021, 07:11:52 PM
Quote from: Sin_Tiger on January 18, 2021, 05:02:27 PM
If you get a really chewed one that just isn't going play and has you looking for a grinder, there is another option.
And another option is to get a slightly oversizes torx bit and put that in gently... While using a big hammer, usually. So far, that has always worked for me.
Title: Re: A question about your nuts...
Post by: mat-tiger1 on January 19, 2021, 12:18:56 PM
These are useful!  :thumbsup
Around £12 from Screwfix.  :icon_biggrin:
Title: Re: A question about your nuts...
Post by: PeteH on January 21, 2021, 01:39:05 AM
All the bolts came out ok when I  changed the discs on my old girly, I even went and bought her new disc bolts....because she was worth it  :nod
Title: Re: A question about your nuts...
Post by: Lee337 on January 21, 2021, 01:27:39 PM
There is a school of thought that says the bolts should be replaced every time as they stretch when torqueing them down.

While I've never done that myself, I can sort of see the sense in it.
Title: Re: A question about your nuts...
Post by: Sin_Tiger on January 21, 2021, 01:48:26 PM
They're not designed as a "stretch" bolt as the shoulder comes into play. Having said that, I don't reuse disc bolts that I haven't removed from a wheel myself. I don't buy used bolts and don't sell them either, I just couldn't sleep at night if anything went wrong.
Title: Re: A question about your nuts...
Post by: blacktiger on February 12, 2021, 02:02:32 PM
Disc bolts are fine to re-use so long as you torque them correctly and locktite them in.
Title: Re: A question about your nuts...
Post by: Sin_Tiger on February 12, 2021, 05:38:25 PM
I don't mind re-using bolts I've ridden with and removed myself. I would NEVER buy used disc bolts though  :nono
Title: Re: A question about your nuts...
Post by: Bixxer Bob on February 14, 2021, 09:21:12 PM
Ditto!
Title: Re: A question about your nuts...
Post by: London_Phil on February 14, 2021, 10:23:09 PM
More likely to fubar the head getting them out...
Title: Re: A question about your nuts...
Post by: ssevy on August 12, 2021, 02:41:32 PM
Sorry for the really late comment, but since folks dig up these older threads while searching...

I often use a dab of grinding compound on the tips of bits and screwdrivers when trying to get out fasteners that I know will be apt to round out. For an allen head, I put it just on the sides and not the tip, so that when I tap it in with a hammer it fully seats. The micro grains of the compound seem to bite into the surfaces of the flanks of the bit/fastener while taking up that really tiny gap that lets the bit bypass the flanks and run out. The careful tapping in of the bit with the hammer is absolutely key to the whole endeavor.
Title: Re: A question about your nuts...
Post by: Madruss on October 09, 2022, 01:27:46 PM
Great information once more. :><
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