disc brake IS threading / bolts

[silva]

Fixed gear, cog to be mounted on a hub with an "IS disc" flange (Surly).
With common ISO thread / bolts, one can screw in the bolts by hand until the bolt heads reach their end, and a tool has to be used to tension them.
With this IS disc, I can only screw the bolts in by hand a few threads, then I have to use the tool already, and the force that I have to use in order to screw further quickly becomes so excessive that the alu of the flange must be damaged.
Both my wheels / hubs showed this problem, as solution I used the nr3 (1 ring / 2 double ring / 3 no ring) of a M5 thread tap set.
During the tapping I had to use a constant force (now and then a turn back to break the curl) from beginning till end.
What can explain this apparent difference in thread?
I used ISO metric M5 bolts, sold as ment for this application (disc cog).

 

[keithmac]

I come across two M5 tap sizes normally working on Japanese bikes, can't remember off hand but its M5x0.8 and M5x0.9 possibly?.

You've either cut a different thread to accept the bolts OR the orignal tap was worn when running the thread.

Sounds like the former if it bound up after a couple of turns though..

 

[Pale Rider]

Not sure I grasp the OP, but Surly is mentioned.

Surly being American, is it possible the original thread was imperial/AF - American Fine?

 

[Venod]

Metric Course is 0.8 pitch

Metric Fine is 0.5 pitch

The most common for bike use is 0.8 pitch, bottle cages mudguard mounts etc.

 

[silva]

Take into account that the mount "IS disc", which is International Standard / ISO, and that the mount is ment for the rotors of disc brakes, here "hijacked" for a rear cog. So the bolts should be the same as anyone with disc brakes on this mount uses.

 

[silva]

I come across two M5 tap sizes normally working on Japanese bikes, can't remember off hand but its M5x0.8 and M5x0.9 possibly?.

You've either cut a different thread to accept the bolts OR the orignal tap was worn when running the thread.

Sounds like the former if it bound up after a couple of turns though..

Either the thread was damaged when delivered, and my tapping repaired it, either the thread was created like that (by Surly), and I cut a different thread.
Since it's aluminium the option was there to use a tap that doesn't cut but deforms, that would result in stronger thread and no lost material, but I don't have such a tap so couldn't.
I doubt the thread was damaged when delivered, since I had to tap through the very end, and the bolts were much shorter.
The first time / wheel, the longer replacement bolts could be turned to the depth of the old bolts, the rest I had to tap out. This suggests that the old shorter bolts also damaged/changed the thread.

 

[silva]

Yesterday I decided to just ask Surly and just got the answer already: the thread pitch should be 0.8 mm, which is indeed the ISO standard for course (not fine) thread.
Both grade 304 stainless steel and 12.9 grade common steel bolts were ISO standard.

Also this advice was added:
"I would very highly recommend that you use disc brake rotor bolts that have blue thread locker on them and that you check them regularly."
The one that mounted it on the new bike used red loctite.
I never used loctite / don't have it anyway, first I used oil, now I use grease. I do check them regularly, although if I see that I cannot retension them X times in a row then I cease checking. In the case motoroil, usually after 3-4 rides of 50-60 km it's not needed anymore. The case grease I just used for the spare wheel so don't know yet.

So I still don't know why I had to tap out the thread in Surly's hub in order to get the bolts in.
As far as I know, according to the specs, the hub is made from an aluminium grade so I doubt any coating that may have been deposited on the bolts holes thread too, was applied. Think I'm gonna need to ask Surly specific, explain why I asked.

 

[keithmac]

Yesterday I decided to just ask Surly and just got the answer already: the thread pitch should be 0.8 mm, which is indeed the ISO standard for course (not fine) thread.
Both grade 304 stainless steel and 12.9 grade common steel bolts were ISO standard.

Also this advice was added:
"I would very highly recommend that you use disc brake rotor bolts that have blue thread locker on them and that you check them regularly."
The one that mounted it on the new bike used red loctite.
I never used loctite / don't have it anyway, first I used oil, now I use grease. I do check them regularly, although if I see that I cannot retension them X times in a row then I cease checking. In the case motoroil, usually after 3-4 rides of 50-60 km it's not needed anymore. The case grease I just used for the spare wheel so don't know yet.

So I still don't know why I had to tap out the thread in Surly's hub in order to get the bolts in.
As far as I know, according to the specs, the hub is made from an aluminium grade so I doubt any coating that may have been deposited on the bolts holes thread too, was applied. Think I'm gonna need to ask Surly specific, explain why I asked.

Was the hub threads clean or did they have Red threadlock residue on them?.

Red threadlock is normally permanent.

I use Granville Blue thread lock on disk bolts (just a drop on each) and that is designed to be removed again.

I've had to tap bike wheels to remove the old thread lock (I've seen it grab well enough to snap bolts!).

Just depends if your hubs an bolts were both clean?.

You can't really get away without removing material when cutting threads unfortunately, I have "thread chasers" to clean up deformed threads but even these remove some.

Plenty of cutting oil makes it easier and stops the tap binding, aluminium is a pain as it's so soft to start with.

I've seen aluminium castings where the manufacturer has fitted steel inserts from the factory but overkill for a hub.

 

[Levo-Lon]

I come across two M5 tap sizes normally working on Japanese bikes, can't remember off hand but its M5x0.8 and M5x0.9 possibly?.

You've either cut a different thread to accept the bolts OR the orignal tap was worn when running the thread.

Sounds like the former if it bound up after a couple of turns though..

All i could suggest is thread pitch..

Already sorted..

 

[silva]

Was the hub threads clean or did they have Red threadlock residue on them?.

Red threadlock is normally permanent.

I don't know, couldn't see it from the outside of the hub. All I know is that the original bolts were 8 instead of min 12 mm long, that after unscrewing I saw red residue at their ends/tips, and that the longer bolts I wanted to replace them with, could only be screwed freehand till the depth of the original short bolts. With an allen key, I still had to use abnormal force and since aluminium thread is weak I decided to tap the thread through.
Initially, I thought the thread got damaged by the red loctite sticking to it when unscrewing the bolts.
But the second rear wheel, bought as a spare in case of trouble, no residue on the bolts, same problem.
In both cases, I had to tap out the entire depth / tap through, and since the loctite likely didn't reach beyond the bolts length, it looks like the hubs thread as it was manufactured by Surly, differed to the bolts somehow.

Will see what Surly will reply on the problem as described fully.

 

[Venod]

I don't know, couldn't see it from the outside of the hub. All I know is that the original bolts were 8 instead of min 12 mm long, that after unscrewing I saw red residue at their ends/tips, and that the longer bolts I wanted to replace them with, could only be screwed freehand till the depth of the original short bolts.

Perhaps the holes were only tapped to the depth of an 8 long bolt, which is sufficient to hold a disc rotor, the taper of the tap would have formed an increasingly shallow thread in the remainder of the hole, hence the tightness of longer screws.

 

[silva]

The holes aren't blind, they go through and the thread too. The 8 mm was the entire length of the thread part of the bolt so with the 4 mm cog causes less than 4 mm engagement remained while cog sellers specifications state 12 mm bolts. I use 16 mm bolts since I had to insert 4-5mm spacers to get the chainline right. This aside ofc.