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Added to which - maybe there was a material failure there and that contributed / caused the [initial] failure?
Absolutely, just put it down to experience and don't loose heart over it.
I'd refuse to believe that there is anyone, with any kinda fettling background, that's not found themselves staring in horror at something [similar] and wondering how on earth it happened.
In a similar vein to the camshaft tale above ^ a pal and I once walked [for what felt like miles] along a main road with a big box, collecting as many of the fragmented bits of his motorbike engine as we could find, after he'd replaced one of the bottom end shells and 'bolted it all back up properly' late the night before, in a barn where he was working.
We never did find everything, not that it mattered given that it was completely and utterly annihilated. When we stripped it later that day, it was scary how much damage had been caused, there was almost nothing we could salvage.
🙄
I think he mostly wanted it done as a kinda public service, just to tidy up all the bits of metal from all over the road.
What type of torque wrench are you using?
or
The top one isn't much good on lower torques such as your stem and they should always be returned to zero after use otherwise it knackers up the calibration.
It sounds like there was a fault with the bolt or threads, it shouldn't snap being 25% over torqued, trouble is now you have drilled it you can't try the warranty route.
We all make mistakes and even with experience you'll still do it. I recently cracked an alloy head trying to remove a broken exhaust stud which cost me £300 and hours of work. It happens, hindsight is a wonderful thing!
The bolts can be very stiff on sunline stems I always greased mine well
I still don't see the need for torque wrenches, I've never snapped or stripped a bolt through over tightening, and only had a few things loose. This includes wrenching at a few lbs'. I'm no mechanical genius either.
I always put the bolt in & run it all the way down to make sure the thread is deep enough & isnt binding. Crucial with smaller/finer threads.
For it to snap like that I'd wager the thread wasnt deep enough & it was binding before it was actually clamping.
Of more concern would be the accuracy of your torque wrench. That sounds like a low figure for shearing an M5 bolt ?.
And as above, anything under 10Nm go as tight as you can holding the short end of the key.
Al - leaving bolts too loose is nearly as bad as too tight and stripping them.
You do need to learn the feel for when a bolt is tight enough. with your amazing skills in all areas of MTBing I am astounded you dont have this.
Ive effed a Hope XC rear through nothing but anger and a hammer and two shimano XT brake levers by trying to get them to fit over funny bulges on my carbon bars.
OK I admit I skim read this, but was it a steel bolt into an alloy stem? If so the stem threads would have gone long before the bolt snapped I would have thought - therefore faulty bolt, but unfortunately you've drilled it so I guess no come back.
I've stripped threads but never snapped a bolt - seems strange.
http://www.torqueleader.com/products.asp?id=345
tool porn. I've got one for bike stuff and another for doing landrover timing belts, far better than click/break types.
One more thing to consideer.
How were you tightening the stem bolts?
If doing up the faceplate on a four bolt stem, you need to bring all four bolts up to torque together, do not tighten one then the other, then the other etc.
If the faceplate is wonky and you tighten one bolt, then another, the first bolt head can be put under a lot more strain.
If you were to just crank up the bolts to 8nm one at a time, i am not surprised one snapped.
If you smoothly tightened them, in a pattern that means you tighten; bottom left, top right, bottom right, top left. Moving diaganally across the bar, and repeat, getting slightly tighter and tighter each time, then I bet you can achieve the recommended torque easily without snapping anything.
And also remember to grease the threads, so that they turn smoothly and don't bind.
Personally, i would use a t-bar allen key to spin the bolts up, then bring the bolts up to torque as above, probably tightening each bolt seven or eight times by feel. Then check with the torque wrench. By doing it this way i am 100% confident that the stem faceplate i tightened correctly.
And 12nm on a stem seems very very tight. Most modern stems using an M4 bolt are 5nm, the Sunline is 6nm. A fourbolt faceplate holds that bars very tightly and shouldn't need excess bolt tension to hold it.
Hi, it was actually a steerer clamp bolt that went, not a faceplate one. I had been tightening them up alternatively, a bit at a time. I think that I'd realised that I over torquing it but the brain didn't reach the hand in time. I've only got myself to blame, I'm just really upset about it as I'm generally pretty careful. It was a 2-24Nm rated clicker torque wrench by the way and I always reset it to 2Nm (it's minimal setting) before storage.
My old stem that states 12Nm for the steerer clamp is a Raceface Deus (old model), it states 10Nm for the faceplate is a 2 bolt design.
My usual approach to bolts is to do them up by hand to roughly where I think they should be and then nip them up with the torque wrench. In this instance the bolt kept turning and broke before my brain activated. I should have stopped and at least re-checked the torque settings marked on the step. I guess it was a lapse of concentration, but a potentially costly one.
TandemJeremy - Member
Al - leaving bolts too loose is nearly as bad as too tight and stripping them.You do need to learn the feel for when a bolt is tight enough. with your amazing skills in all areas of MTBing I am astounded you dont have this.
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My point is you (one, I) CAN do it by hand (can see the need for carbon, cars etc)
Oh I still can't do front wheel lock-ups.
If it's a steerer clamp bolt then can you not drill it right through and fit a top hat sleeve from the far side if helicoiling is not feasible. A cruder way would just be to use a longer bolt with a nut on the far side.
I'm surprised, like others, that the bolt snapped before the alloy stripped. But, yes, we've all done something similar at one time.
I learnt my mechanicing skills on an expensive parentally-funded orange patriot when I was racing DH as a kid.
Cue lots of broken marzocchi stanchions from overtightened crown bolts, stripped BB shell on the brand new, back from warranty front end, three knackered freehubs because i thought it would be a good idea to fill them with GT85 from new, not to mention a set of Ti handlebars I found in my dad's cupboard which I promptly crimped by overtightening them in my stem.
one of many reasons I now shy well away from expensive DH toys!
Thanks for sharing your disasters guys, I guess I shouldn't take it too hard, after all I do seem to have come a long way with my mechanical skills; perhaps I got a bit complacent. It's just frustrating when I realise just how many options I have for not screwing up or salvaging the situation without making it a total disaster. I'm sure I'll be better focused next time!