Shock Mount Cross Thread

I'd try running the correct size tap through it first, then look at options like helicoiling if that doesn't work.

@coatesy thanks, I'll pick up a tap set tomorrow. I've not used one before but I assume they are fairly simple to use though I can't see how I am going to get the tap perpendicular to the thread whilst going through the frame as the tap looks to be longer than the distance between the two threads on either side.

Are both sides of mount threaded? Or just the far side? As that could make things tricky

@weeksy looks like just the far side

That's where the problem may be then? Eg the thread tap will end up cutting a thread in both sides? Unless the internal diameter on the first side is larger?

@weeksy oh! I was thinking I could slide it through and then thread the far side only but of course, I see what you mean. Do I have any other options? Could I tap a thread on the near side even though I don't need it?

Have you got any pictures of the tapped hole & the bolt? Buying taps & cleaning out the thread is definitely worth a try. Have you used a tap before? It's a straightforward job but I've seen people make a complete horlicks of cleaning out threads in alloy & ending up with no thread rather than a nice clean one.

Pictures would definitely help.

@Davesport never used a tap before no, sounds easy but probally isn't. I'm trying to work out how I can even get a tap in to where I need as I need to pass though another bolt circle en route. Let me try and get some pictures

The tap is unlikely to be bigger than the unthreaded side, if it was then the bolt wouldn't fit through it. As said above, it's not too difficult, but if you're unsure then consider letting somebody with experience either do it, or guide you through.

The tap is unlikely to be bigger than the unthreaded side

@coatesy this is what I am really hoping. Tapping theory sounds easy enough but I guess if it goes wrong it goes very wrong.

Stripping a bolt while undoing it out of a fairly new frame would be quite unusual IMO. Are you absolutely sure this is what has happened?

The tapping side of things isn't that tough mate in honesty... i've done 4-5 now and before doing my first had done 0.

I'm not convinced i'd let me start on a piece of metal without a hold already in place... but with one that's not quite right, it's a fairly easy job.

Is the tapped hole blind or open on the other side? If it is open then running the bolt in from the other side should clean the thread. Standard trick for pedal threads.

@nickjb good point, the hole on the other side is open I believe. The bolt does catch on the frst turn but then offers up resistance. Let me give that a try as otherwise I am retapping anyway

@weeksy nice OK I'm pickup up a set later today so I'll give it a go, I'm not always the most patient with these things but I'll try and find some old broken parts and do a few practice runs

good point, the hole on the other side is open I believe

that's a great start !

@stuartlangwilson when I loosened the bolt it felt slightly tight, as in it almost gave a slight grinding towards the end. I initially offered the bolt up to the thread on reassembling and it initially went in fine but as soon as I tightened it I could feel resistance so it's absolutly possible that I had cross threaded it on reassembly (i do have previous lol) however the fact that it felt odd when I took it apart made me think it was probally overtightened originally?

I am not sure that the thread is even stripped as I can get the botl to catch on the thread and then about a half turn way in it resists. Looking at the thread and bolt it actualyl all looks to be in good shape and I had not obvious bits (swarf) come out like you would do normally.

where you based ? i've got a tap kit in West Berks if it helps.

Is it just gummed up with threadlock?

@nickjb threading the bolt through from the other side, the bolt goes in up to the point of the first thread from the correct side, so it goes in clean over most of the thread however it butts up against the damaged thread. So there is definalty an issue with the first thread

Do you know what size thread and the pitch, can you measure the pitch?
Make sure it's correct before you go shoving a tap through. Would be a shame for you to wreck the frame by going from intweb advice.
Can you get a helicoil (drill bugger and cut a bigger thread) in there if you get it wrong?

Get someone who knows what they are doing to have a look at it.

Or at least post some photos of the frame thread and the bolt before going down the route of potentially doing it wrong.

@weeksy I'm oop north but thanks for the offer. I'll pick one up as I am sure I'll need it again sometime

@K it's proving to be very difficult to photograph though while looking at it much more closely I could see that part of the thread is damaged, the damaged thread shaving was still attached to the thread and while cleaning inside it came off and out.

I believe the tap kit has a gauge but yes good advice I won't be rushing in to use it until I am confident that it's the right thing to do.

The frame is carbon and the original thread appears to be a helicoil though I can't say for certain that it's possible to drill bigger and reinsert. If the original is heli is it possible to take it out and reinsert a new one?

the damaged thread shaving was still attached to the thread and while cleaning inside it came off and out.

Have you tried putting the bolt back in from the wrong side again? You may have sorted it by getting the bit of swarf out.

@tthew just tried that and no good, it still gets stuck unfortunately

If its got a helicoil in do not try to put a tap trough as it will likely get jammed in the flutes. It could be that the end of the helicoil is dameged, in that case you'll need to pick it out and extract it and put a new one in. Or carefully grind the damage off with a mounted point in a die grinder or dremel.

I've uploaded images to a different forum, can somebody tell me if what I have is already a helicoil?

https://www.mtbr.com/threads/thread-on-rear-shock-mount-has-gone.1205414/#post-15650731

That's not a helicoil, it's a thin-walled insert. Carefully running the correct size tap through it from the outside should sort it out.

That looks to me like an bonded in alloy insert not a helicoil but I am far from sure. It could be a helicoil in the alloy insert which would actually be good engineering practice. If the part the female thread is in is alloy and a steel bolt was in it and locktited in then its possible that removing the bolt has taken the thread with it.

Given the value of the frame and your doubts I would be taking it to an engineering shop not a bike shop for an opinion

If the thread is damaged and you run a tap thru it you will clean up the thread but it will be weaker than it should be as you have removed some of the threads

If this is the first time you've taken the bolt out I assume its still under warranty? I'd be starting a claim saying that they insert has fallen apart on removal of the bolt. There are many good suggestions above, but it would be worth checking your warranty situation first as you could find yourself in a far stickier situation if an attempt at fixing goes sideways

Edit: looks like a 5 year warranty, would definitely be getting in touch

@mashr hm OK good idea, I will contact YT as to their credit they have been excellent so far when dealing with them. Funnily enough I was just in process of considering ordering a new bike from them.

@doomanic when you say from the outside, do you mean as in the same way that the bolt would go in?

Nope, go in from the back of the hole (opposite direction to how the bolt fits when the bike is built), the thread is the same all the way through.

That way you can spin the tap in along the good threads with just your fingertips (which ensures it is aligned correctly with said threads) before it cuts out the damaged portion of thread.

@oldnick ah OK yes, that makes a lot of sense

So YT have responded to my warranty claim already stating that they are able to collect the bike and inspect. Obviosuly no guarntee at this stage whether they will be able to do anything but very impressed to hear from them so quickly.

I also now have a tap set with gauge so I know that I am dealing with an M8 1.25 though I couldn't fid any cutting fluid, I do have WD-40

The question now for me is really one of risk, do I tap and hopefully ride, or do I stay safe and send to YT for inspection? Obviously sending to YT is the sensible thing to do however the odds for a repair do so far seem stacked in my favour.

I'd say let YT have a look and see if you can benefit from their warranty.  If you've never had the bolt out before it will have been caused as the bike was assembled.  It'll be hard not having a bike if the weather is good and the trails are running well though,,.

I'd be using the tap and riding my bike.

It’ll be hard not having a bike if the weather is good

@Rivett rightly on wrongly - this is playing a large part in my decision making process lol

I'm not sure that I would be lucky enough to just have YT turn around and say they repair/replace and I can see me having to go to alot of effort sending them then bike only for my claim to be rejected.

On the other hand if I bodge the retap I am not sure where I can go from there.

On the chance that I am not successful reatpping the thread myself, can the insert be replaced by an engineering company does anybody know?

I've just tested out my tap set on some old parts and it's actually a very easy process so long as you are careful (strangley it's very satisfying to do)

anyway, I took an old post mount adaptor and retapped from the front and back a thread which was good if a little stiff and after retapping, it was smooth as butter. I then purposely cross threaded one and retapped that from the back with success (attempting from the front would not happen so thanks to whoever gave that bit of advice)

I am feeling quite confident about retapping at this stage so far but I am going to look for an old star nut as I believe they use an insert, whereas the post mount adaptor thread is machined into the thing itself.

The only thing I was a little unsure with was the Tap Wrench as the tap bit although completly straight, did tend to work it's way loose towards the end. Maybe not a huge problem once it's engaged anyway I suppose.

Does anybody know how far beyond the hole I need to go when retapping? Any other adviced is appreciated as I am way out of my comfort zone here

You’ll feel when it’s gone all the way through. It’ll tighten up as you get to the damaged thread and then ease off as the tap cuts the damage out.

sounds about right doomanic.

good news, I have successfully retapped, the bolt can now go in and out easily and after cleaning the bolts down they were caked in so much threadlock I am sure that was the cause of the issue.

Initally after retapping I still had the bolt resisting at different points so I took a pin to it and removed a load of threadlock and it now goes in easily. even after removng a load of it there still seems to be a load on there.

Anyway, thankyou to everybody who contributed, I am feeling very relieved right now. Hopefully the thread is not compromised in any way.

What is the consenses for reassambly, do I really need to be applying so much threadlock if any at all?

A small blob on one side, run it round with your finger so it is all in the thread (not sticking out) and wind it in.

@oldnick should I remove all of the old threadlock before applying or just apply over what's left? it's fiddly to get it out so would rather just apply over the top if that's possible?

Given it's a bike not some NASA probe costing bajillions I'd use a fine wire brush to clean loose gunk out of the bolt threads, then if it threads in smoothly you are good to go 🙂

@oldnick good point - will do, thanks again for you help!

for anybody coming to this in the future, if you are considering retapping this article is a great introduction to the concept: https://knowhow.napaonline.com/know-how-notes-how-to-repair-damaged-threads/

this video was also very helpful: