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I suppose we all have those lapses of concentration every now and then, but this one was costly!
I don't have a lot of cash so was pretty excited to be able to get a £60+ OS Sunline stem and a set of flat bars to finish of my much loved bike. The clamp bolts on my old Raceface stem require torquing to over 12Nm (which is a fair old whack) so I was a bit suprised, after hunting for instruction with the stem (there weren't any) to find stamped on the bottom of the stem in tiny letters 'torque bolts to 8Nm'. I though this seemed a little low but the bolts were thinner M5s. I'm very careful with bolt tightening and use a torque wrench so was suprise and panic stricken when one of the stem clamp bolts sheared off with a bang. I tried carefully to drill out the remains of the bolt but it was pretty hard and I ended up screwing up the thread and rendering the stem useless; I'm also left with a £40 set of oversize bars and nothing to do with them.
Anyway, to cut a long story short, on closer inspection the tiny writing I thought said 8Nm actually turned out to say 6!
I can't really complain (although clearly printed instructions would have been nice) as it was entirely my own fault and hamfistedness, but I'm gutted nethertheless. I'll have to make do with my old stem and bars for the foreseeable future.
Never used a torque wrench on my bike. cant remember shearing/ rounding a bolt or having one come loose either. Just use an allen key!! 8)
Can you not helicoil it?
That sucks - can you not drill it right out and then fit a helicoil?
*Awaits the heros who always remind us that we shouldn't rely on torque wrenches yadda yadda yadda.......*
edit: too slow
n closer inspection the tiny writing I thought said 8Nm actually turned out to say 6!
shouldn't the margin for error be at least 100% ?
Helicoil is a wire insert thread, if you email me I can sort this for you next week
Cheers Mat
shouldn't the margin for error be at least 100% ?
On a bolt torque? No, not unless you want all your bolts to weigh twice as much as they need to to account for hamfistedness.
A good machine shop should be able to redrill, replug and tap it again. Ritchey do a very small torque wrench for stem bolts.
No, not unless you want all your bolts to weigh twice as much as they need to to account for hamfistedness.
like I spend much time worrying how heavy my bolts are ? I'd certainly like them to have a decent safety margin rather than be teetering on the edge of failure all the time...
Whether or not to use a torque wrench is often a contentious question. I work on my own bike as an when it needs work doing, I don't work on dozens every day in a bike shop so have never really developed that much vaunted 'calibrated arm' that others seem to. It's interesting that a some carbon component manufacturers produce pre-set torqe keys for fitting their components; I suspect that many 'calibrated' mechanics aren't quite as accurate as they think.
Anyway, I use a torque wrench and this time it seems to have gone wrong. I may even have sheared the bolt without using one; all the stems I've had before have had M6 clamp bolts and required much higher torques (12-13Nm) than the 6Nm of the Sunlines thinner M5 bolts.
torque wrench
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The problem with torque wrenches is that they have a long handle. A proper set of Allen Keys is made so that the thinner ones are short - and hence can have less torque easily applied.
I'm surprised that you managed to break the bolt at such a low torque to be honest.
I would have thought they would have handled signicantly higher forces than that.
A proper set of Allen Keys is made so that the thinner ones are short - and hence can have less torque easily applied.
Exactly. The same with spanners too. When you're at breaking things levels of tight, you're already thinking "Something's not right here".
Surely if they are M5 there is enough material left to tap M6 or M8 thread into the hole.
Obviously all the old bolt will have to be removed , but with care and a decent tap and some cutting oil you might should be OK
No need for torque wrench!
No need for torque wrench!
Perhaps but I still maintain that you're unlikely to be able to develop a feel for things if you're only working on a bike occassionally and you can still break things without a torque wrench. Going back to carbon component manufacturers producing pre-set torqure keys - I suspect that a lot of people who think that they've developed a 'feel' for torque by falling with the safety margins for metal components find out that they're not quite that accurate when working with carbon.
Anyway, the idea of a torque wrench was partly to help develop a 'feel' by knowing how tight something actually is (rather than simply not breaking something and therefore assuming you're spot on) and partly for reassurance (and yes, I have seen [url= http://www.sheldonbrown.com/tork-grip.html ]Sheldon Brown's torque wrench![/url].
Pjay, would you like to helicoil it for you?
Amos, yes please, I've replied to your email. I'm happy of course to pay for your time and any costs if you think it's worth a try. I did seem to make a fair old mess trying to drill the bolt out, I'm not sure a handheld drill was a great idea, but it was all I had access to.
6-8nm really isnt a huge jump not one id expect to shear a bolt at anyway.
I'm surprised that you managed to break the bolt at such a low torque to be honest
I'm suprised I didn't round out the rather small M5 head long before shearing the bolt.
hindsight,but in future if you shear off the allen head, the threaded bit left in the hole will wind out easy(as its no longer under any torque.tip of a small screwdriver will do it....
Pah! I had an SPD moment and broke my £200 phone on Wednesday
Perhaps but I still maintain that you're unlikely to be able to develop a feel for things if you're only working on a bike occassionally and you can still break things without a torque wrench
Think about it - convert into lbs/ft - 6NM is about 4.5 lb ft. Or in metric it's approx 600 grammes / metre.
So the torque is equivalent to 4.5lbs of weight on the end of a 1 foot lever.
If your allen key's 4 inches long, you need to triple that figure (there being 12 inches in a foot).
So you're talking about force of 13.5 lbs on the end of a 4 inch allen key. That's technically known as pretty tight.
Once you can actually visualise what the torque figures mean, it all becomes a bit clearer.
Q. What is the range of your torque wrench? 0-15Nm will be fine but some 5-50Nm will be terrible and over torque the bolts.
Id have thought torque settings that low were more about protecting the stem than the bolt.
I know a lot of mechanics have this so called integral torque wrench, but I dont think theyre as accurate as they think they are. When I checked the bolts on my new bike I found two that had been stripped, and just tightened up as well as possible on the next thread to cover up and save replacing parts.
Retap the threads for a bigger bolt if the M5 doesn't fit...or helicoil it...
'torque bolts to 8Nm'. I though this seemed a little low
Why? Thomson quote 5.5Nm and they're M4.
My torque wrench is rated 2-24Nm so should be pretty good for most bolts on a bike. I've got a larger 10-110Nm one that I use for cartridge bottom brackets.
The stem does seem scarily light but it is a XC one.
I thought 8Nm seemed a little low as my current Raceface stem is in the region of 12-13Nm for steerer clamp bolts, so that's what I'm used to. I wasn't aware that Thomsons were 5.4.
The other lesson is when you have broken something or something goes wrong with your maintenance STOP!
Have a cup of tea. think, ask advice. Do not reach for the power tools or hammer.
edited out = crossed posts
I accept the point that it will help you to learn the "feel" - it took me a few broken bits to develop it.
You dont just need to feel. You need to listen for sounds that bolts make when you tighten them up. A bolt that is getting tight and about to snap will be creaking like hell.
I feel worse about it this morning than I did yesterday, I suppose it's sunk in. I think it's knocked my confidence more than anything. Over the years I've gone from someone who had to take his bike into the LBS to get punctures fixed to someone who's learnt a great deal and built up (and enjoyed building up) their own bike. I've done pretty well with the latest frame transplant too; when the headset was binding instantly with any preload off I went to the bike shop to get the headtube faced and chased rather than panic and muck things up (the same with a rough BB thread). A silly mistake like this has left me feeling pretty useless and a real numpty (I suppose I'm not the only one though as someone on here unfortunately recently posted about cracking their new carbon bars).
Last year when I partially popped out a brake caliper piston (oil all over the floor) I calmly logged onto Singletrack, got some advice, refitted and re-bled and it worked perfectly; why I didn't do that this time I just don't know!
Amos has kindly offered to have a look at it for me to see if it's salvageable so fingers crossed. At least I've been able to fit the old stem and bars so I can still use the bike!
I wouldn't worry too much - just learn the lessons. Its a part of how you learn to mechanic stuff
the two lessons here are
1) don't blindly trust a torque wrench - continue to think and be cautious using one
2) - when you bust something or a maintenance task goes wrong STOP! Have a cup of tea, put down the hammer or drill.
I did a couple of things like this with my first motorcycle - but I never did them again.
Don't beat yourself up, we've all done it. It's a bike not a nuclear sub.
Sell the torque wrenches and buy a new stem.
Tighten allen bolts up holding the short end of the allen key, long end in the bolt. It is very hard to overtighten doing this, and will get your bolts in the right ballpark tightness most of the time, maybe except for crank arms.
They're two rules I usually adhere to TandemJerry, why I panicked and didn't yesterday is a bit of a mystery. What's particularly gauling is that, as someone has said, once the head had gone there was no torque and I should have been able just to wind the shaft out, instead I made a complete hash of it with a drill!
I shall go out for a ride and try and relax.
s'alrite. I was rebuilding an engine a few years ago and somehow over torqued the camshaft retaining bits in the cylinder head - obviously didn't know at the time.
Started it up, ran smoothly - winner. 5 miles down the road on initial break in run the engine cut out, I thought ****. Got towed home by the AA and went to bed.
Next day, took cam cover off, plugs out, trued to turn the engine over by hand, wouldn't go, double ****!
Out came the tools, stripped the head and both CAMS were scored on their journals and 8 out of 16 retainers were ****ed. So one very very expensive lesson in checking things over before you put things back together.
maybe except for crank arms.
for which the correct torque is standing on the long end of the of the key 🙂
Pjay - we all do these things from time to time - as others have said it's all just part of it ! If you want some therapy have a search for a thread from a few weeks back about things going wrong with bike fettling - you are not alone 😆
here it is :
[url] http://www.singletrackworld.com/forum/topic/most-mind-blowingly-stupid-parts-breakage-youve-had [/url]
You can always ring the Samaritans if you're that gutted 😆
Shit happens - standing back and trusting your gut generally works for me.
A silly mistake like this has left me feeling pretty useless and a real numpty...
If it's any consolation, I'm a professional mechanic and I wrecked a £250 wheel bearing recently.
Regarding drilling it out for an M6 bolt or helicoil.
If you've drilled it off centre, it may be hard to get a helicoil to work. depends just how much of a mess you've made of the hole.
Drilling oversize for an M6 bolt may be a better option. If the head of the bolt is recessed into the stem, an M6 bolt head won't fit. Use an M6 button head screw, as it uses a smaller hex key, and grind the outer diameter down.
In either case, I'd say you're going to need it clamped down on the table of a pillar drill, not free hand in a vice.
A torque wrench is only any good if it's actually callibrated properly I've never bothered with one in over 20 years of spannering. Not needed on a bike IMO. For carbon bits maybe..
Thanks everyone, I've been out for a ride and it's still fun with the old stem and bars. I guess I just need to mark it up as a learning experience and carry on.
PJay - Member
Thanks everyone, I've been out for a ride and it's still fun with the old stem and bars.
The best response yet 🙂