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One of the pinch bolts was rounded on a SLX NDS crank arm, so I tried to drill it out but it's damaged the threads so I was wondering if one bolt would be okay. It's the outer one that's goosed.
What d'ya reckon? I could use a nice long bolt in the remaining one to get a decent amount of force. Normally the pinch bolts are only ~12Nm so not that tight.
It will come loose (or fall off) and you'll trash the splines on the crank arm.
helicoil?
I can sell you a pair of brand new Deore HT2 arms for £15 posted if you like?
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Hmm, I wouldn't personally, very easy to strip the splines on the inside of the crank arm. And one they start to strip you can't put any pressure on the crank arms. Really bad is this happens halfway though a ride
One of my arms has been serving me well with only one bolt for about three years.
Either helicoil, or get a longer bolt and stick a nut on the end.
Personally I don't think it's particularily asking for trouble, and after all the cranks are knackered anyway and buying one replacement arm isn't really economic. So the worst that can happen really if it does go wrong, is it spoils a ride.
[i]the worst that can happen[/i]
is that the splines slip on the axle just as you really put some power through them and you crush a testicle on the top tube/step interface of your bike.
apparently.
ta. Helicoil isn't really possible as it's too much of a mess now...
I guess it'll only slip on the splines if there's not enough pressure holding the arm on. Normally that pressure is two bolts at 12Nm. Would that be equivalent to one bolt at 24Nm...?
I suspect 1 bolt at 24Nm would very quickly result in two sets of stripped threads and no bolts applying any pressure.Normally that pressure is two bolts at 12Nm. Would that be equivalent to one bolt at 24Nm...?
what I meant was I could use a bolt and nut (both steel) at 20ish Nm on the remaining 'good' hole.
how bad is the 'bad' hole that you can't even pass a bolt through it?
Get a zip tie in there, you'll be reet 😉
bad hole could run a bolt+nut I suppose. In short (and I'm sure you've guessed this by now...) I made a right mess of it trying to drill it out 😯 Some days you just don't have the touch...
Ideally I'd 'forget' about the bad hole and just use the good hole. That way it'll still look respectable. But if that's too risky then I'll just nut+bolt the bad hole as tidily as possible and hope it doesn't look too bodged.
Did something similar about a year ago, rounded one of the bolt heads, then had to drill out bolt, (great fun, about 5 bits later). Used a Tap & Die set to re-thread to use a larger bolt, eg 4mm to 5mm (or 5mm to 6mm, cant remember exact size).
Seems fine, been ridden 1-2/week for last year, but no doubt will fall off tomorrow to spite me.
should be quite easy to sort. Drill and re-tap larger if there is material there. Also enlarge the counterbore for a bigger screw head and/or grind down the head a bit.
If you call it quits and get some new ones then give me a shout.