- This topic has 41 replies, 25 voices, and was last updated 12 years ago by RustyNissanPrairie.
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Heeeelllllllllllllllpppppppppp! De-threaded brake mount on fox fork!! AAArrrgghh
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MoolyFree Member
So I thought I would save a few quid and change the break pads on my bike instead of taking to the LBS and paying for the privilege.
While trying to get it all lined up I ended up partly de-threading the mount on my fox forks.
I can still get the top bolt in but am very careful as i`m sure its only holding on with a few threads.
The questions are:
Is this solvable with a slightly longer bolt to get more purchase? If so where would i get one?
Are the Forks completely knackered and need replacing?
Could i get the forks re threaded at a slightly thicker gauge and increase the bolt size?
Is it safe to ride as is?
Am I the only Muppet to have ever done this and landed myself with a huge repair cost for replacing the forks?
Any help greatly appreciated. 😥TandemJeremyFree MemberHelicoil is the answer A few quid from a engineering place
TandemJeremyFree MemberIts a coil that works like anew thread – run a special tap thru the hole then inset the helicoil which is like a spiral wire. You get a new thread that is steel the same size as the original
grim168Free MemberYou drill out the old thread and tap it to a bigger size then screw in a thread insert which gives you the size of the original thread
MoolyFree MemberSo where would i be able to get this done or is it a case of doing myself. Considering i have just stripped the thread of the fork is it sensible to do myself?
argooseFree MemberDone the same on a set of bombers, longer bolt from halfords all sorted. If you go helicoil get it done by engineering firm or fork will be ****
Burls72Free MemberFrom the sounds of it you might be able to save the threads by running a tap though them. I say this without offence but i’d ask a friend with more mechanical knowledge than you to do it. If they can’t be saved fitting a heli-coil would be beyond your mechanical skills. Sorry not trying to be horrible just trying to save you knackering up your forks.
NorthwindFull MemberA longer bolt might well be all it needs. Definately needs to be tried.
chrisdwFree MemberI had exactly the same happen a short while ago…
I bought one of these… http://bit.ly/zgrzQQ
Followed the instructions and its all sorted!
I also watched a YouTube video to aid the instructions, but its damn easy.
porter_jamieFull Memberif you have to ask how to do a helicoil then imo you should get a pro to do it for you (because your lovely fox forks are worth lots of money!)
you could buy a kit and practice on some spare bits of ally i suppose, they are about 40 quid for an m6
http://www.mscjlindustrial.co.uk/CGI/INPDFF?PMCTLG=00&PMPAGE=243&PMITEM=EHC-35060B
edit add – the ebay one is well cheap – but i would be a bit suspicious of it myself, the JandL one is gen Helicoil.
stAn-BadBrainsMBCFree MemberYou need to find a local engineering firm. Someone at the local garage may also be ableto assist or put you in touch with a decent engineer.
If your confident you could DIY destructions here
TBH I’d probably pay and get it done proper. I used to work in a machine shop and its much easier with experience and the correct tools
XXXFree Membersome of the more specialist motorbike shops do it . Had to get one put in whilst in spain on holiday once, impressive given my Spanish. l’m always surprised that cycle shop don’t do it…..
NibsyFree MemberA helicoil will work for a while but isn’t highly recommended due to the fork material, magnesium I believe. The true solution is new lowers for about £150.
porter_jamieFull Memberps, if you are anywhere near essex myself or my brother will do it for you – we have a small engineering shop near basildon, and have done loads of helicoiling. I’m sure we have M6 in stock. It will cost you a pie, or a cake, not fussy.
chrisdwFree MemberI wouldnt bother going to a firm for it.
Because you are only drilling out a tiny amount of metal from the outside of the hole it is very easy to do. And the kits from eBay (see above) are only £8
The riskiest bit is the tapping, but you really would have to be a mong to mess it up, just keep it straight ish and screw it down 2 turns then back 1 till it stops. Keep it lubed with a bit of chain lube or something.
Watch this video…
[video]http://www.youtube.com/watch?v=RFYa6sjhh_E[/video]AmosFree MemberI don’t agree a helicoil will be a permanent fix if done properly, much stronger than the original thread, in fact we helicoil magnesium for that reason so as not to strip the threads. Op where are you based? I could look at it for you if you liked
geeFree MemberI helicoiled one on a really old set of SIDS which had had brakes repeatedly fitted/removed. That was over a year ago and it’s been fine.
MoolyFree MemberCool – thanks for all the advice. Think I`ll go with the slightly longer bolt and then if still having problems contact the local garage for advice on getting heli-coil installed.
I know the LBS are keen to sell a new pair of forks but thought they may have suggested the above unless it`s an insurance thing that they have to cover their behinds.NibsyFree MemberI wasn’t paying for a new set of lowers when it happened to mine as a bike shop did it. Obviously I didn’t want it helicoiled as I hadn’t stripped the thread myself. Also, mojo recommended not to helicoil but seeing as they sold the new replacement lowers why would they.
MidlandTrailquestsGrahamFree MemberLonger bolt would be the easiest and cheapest option if possible.
Find a long M6 bolt and screw it in as far as it will go.
How far will it screw in ?
How much engagement was there with the bolt that stripped the thread ?
If there’s 5mm or more difference, it should be OK.I take it you’ve got a 160mm disc if the caliper mounts directly to the fork ?
You could go for a 180mm disc and a +20mm adapter. That way, once the adapters fitted, you should never need to touch the bolt again.Burls72Free MemberI’d borrow a tap and run it through the threads first and use a new bolt.
MidlandTrailquestsGrahamFree MemberNormally, if you just buy “a tap” it will be a taper tap, which is not much good for a blind hole.
You’ll need a plug tap to reach the bottom of the hole.Burls72Free MemberFair enough I should have said borrow a final stage tap or plug tap. It still doesn’t change the fact that the threads should have a tap run tnrough them. Cleaning the threads by running a tap through does no harm but can save no end of trouble.
transappFree MemberFind local engineering firm, call and ask if they’d helicoil or retap a single hole for some petty cash money. This cash will go straight into a back pocket, but don’t let that worry you. It’ll be cheaper to get someone to do it after you’ve bought the bits. Where are you based?
Oh, and the guys i used to work with would have that sorted in sub 5 mins, really you’ll not have an issue at the right place.
TandemJeremyFree MemberHelicoil is the right and permanent answer. Retapping will not work if the thread has been ripped out, longer bolt will only get a bite in the bottom of the hole. %mm you say MTQG – I want a lot more thread than that holding my brakes on.
helicoil is permanent and stronger than the original thread
thomthumbFree Memberi’d want 6 – 10 mm engaged on a m6 thread.
i’m not sure i’d advise someone who crossthreaded a bolt to tap in a helicoil. no offence meant. 😀
Burls72Free MemberHelicoil is the right and permanent answer. Retapping will not work if the thread has been ripped out, longer bolt will only get a bite in the bottom of the hole. %mm you say MTQG – I want a lot more thread than that holding my brakes on.
helicoil is permanent and stronger than the original thread
It’s hard to say without seeing it but my understanding from the op’s description is that he has just gone in on the wrong angle at the start of the threads. If thats all it is then clean the threads up, new bolt and it will be fine especially if it’s 160mm and go up a rotor size as MTQG suggested. If the bolt had been done up to tight and stripped the threads then yes i’d agree a helicoil is the only option.
igmFull MemberWeren’t old IS mounts wonderful. The answer then would have been “buy a new £10-20 mount”.
Good luck – and for what it’s worth I’d helicoil it.
dadandladFree MemberIf the screw is highly loaded e.g preloaded and is screwed into a material of lower strength than the screw then a detailed assessment of the joint must be carried out to ensure that thread stripping will not occur.. Unfortunately the option of increasing the depth of the tapped hole is of limited value as it has been established that there is no advantage if having a thread engagement in excess of the nominal screw diameter. The problem is that the load taken by the screw is not evenly distributed. The majority of the load is taked by the first thread and very little of the load is taken by the fourth thread onwards.
The preferred options are to design the joint to based on the use of suitably rated nuts or ensure the screw and parent metalof the female thread,have similar mechanical strengths.
When the design is based on highly loaded /high strength screws fastened into threaded holes in components with lower strengths then it may be necessary to use thread inserts.
Types of Thread Inserts
Helical Wire Inserts (Heli-Coil)
The helical wire inserts inserts, generally identified by the tradename Heli-coil, are made from diamond shaped wire formed into coils. They are screwed into tapped holes such that the resulting internal profile of the coil is that of the desired female thread. The tapped hole is created using a special tap . The insert is over-sized so that it anchors itself into the hole. Some have tangs to enable convenient install but some do not. Special tools are required to install the inserts. When the insert includes a tang , it is snapped off after installation. The insert can be configured to provide a thread locking duty.
The resulting female threads are strong because the flexibility of the insert provides an even distribution of loads throughout the length of thread engagement. This flexibility also compensates for variation in the formed thread allowing each coil to carry its share of the load. The limitation on length of a convenional thread are overcome with this component and the load can be distributed over thread lengths far in excess of that in a tapped hole with no insert.
The heli-coil internal profile is hard and polished dramatically reducing thread wear.
neninjaFree MemberI Helicoiled a previous fork when this happened. I think it cost something like £15 to do both threads at a local precision engineering company.
The end result was a thread that was more perfect than when they left the factory and probably stronger too.
Burls72Free MemberIf the screw is highly loaded e.g preloaded and is screwed into a material of lower strength than the screw then a detailed assessment of the joint must be carried out to ensure that thread stripping will not occur.. Unfortunately the option of increasing the depth of the tapped hole is of limited value as it has been established that there is no advantage if having a thread engagement in excess of the nominal screw diameter. The problem is that the load taken by the screw is not evenly distributed. The majority of the load is taked by the first thread and very little of the load is taken by the fourth thread onwards.
The preferred options are to design the joint to based on the use of suitably rated nuts or ensure the screw and parent metalof the female thread,have similar mechanical strengths.
When the design is based on highly loaded /high strength screws fastened into threaded holes in components with lower strengths then it may be necessary to use thread inserts.
Types of Thread Inserts
Helical Wire Inserts (Heli-Coil)
The helical wire inserts inserts, generally identified by the tradename Heli-coil, are made from diamond shaped wire formed into coils. They are screwed into tapped holes such that the resulting internal profile of the coil is that of the desired female thread. The tapped hole is created using a special tap . The insert is over-sized so that it anchors itself into the hole. Some have tangs to enable convenient install but some do not. Special tools are required to install the inserts. When the insert includes a tang , it is snapped off after installation. The insert can be configured to provide a thread locking duty.
The resulting female threads are strong because the flexibility of the insert provides an even distribution of loads throughout the length of thread engagement. This flexibility also compensates for variation in the formed thread allowing each coil to carry its share of the load. The limitation on length of a convenional thread are overcome with this component and the load can be distributed over thread lengths far in excess of that in a tapped hole with no insert.
The heli-coil internal profile is hard and polished dramatically reducing thread wear.
I’ll admit i’m no engineer but from my understanding the above applies when you are designing something from new. It’s designed to withstand x pressure then it’s multiplied by the relevant safety factor, times 3,4,5, etc. Fox have already designed the fork material, the thread design and the size of the bolt required. Say for example the bolt is 40mm long, the first 6mm (because it is a 6mm bolt) gives the majority of the strength to the joint. If that first 6mm is missing the next 6mm will give the same strength ratio because it is the first 6mm. It’s no different than a say having a 10mm recess for a locating dowl.
NorthwindFull MemberObvious cut-and-paste is obvious. And not very relevant tbh.
The thing about the longer bolt, is that some people seem to be assuming it’s weaker. No reason to assume that this is the case- there was very likely unused thread before this damage occured, so it may well be that a longer bolt will end up engaged into more thread than the standard setup had, ie be exactly as good. Equally, it may not- depends on the fork and the damage.
Jumping straight to helicoiling before eliminating that as an option is a mistake.
Burls72Free MemberJumping straight to helicoiling before eliminating that as an option is a mistake.
+1. Last resort.
slinkybikeFree MemberI would be happy to get it helcoiled but just a word of warning I saw a set of lowers helcoiled and they were drilled too deep and the lowers started leaking. 😀
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