Yet Another Cycling Forum
General Category => The Knowledge => Topic started by: andyoxon on 29 March, 2021, 01:00:31 pm
-
:-\ So I've managed to shear off a bolt in a left arm 105 5703 (HT2) left crank arm. I've removed/attached these many times (on another crank set). I think my mistake on this (acquired SH) was not removing the bolts and greasing first. It was weird because I was alternately 1/4 turn tightening with a torque wrench set to 14Nm, and one bolt reached torque and the other didn't at the same time, so I did an additional 1/4 turn and it bolt head has sheared off. Whether bolt was already damaged don't know.
Drill it out? How would I do this?
Replace crank arm is an option. Anyone know if 105 5703/5800/R7000 LH cranks are essentially the same? Diameter of HT2 axle? It's a silver 172.5mm.
Other thoughts?
-
Automatic centre punch.
Punch an indentation in the bolt, close to the circumference.
Repeat in the same place several times to deepen the indentation.
Place the punch tangentially in the indentation, and operate the punch.
The remains of the bolt will start to rotate in the direction you are operating the punch.
Repeat. Many times.
It'll take a while, but it is by far the easiest method I have found for removing sheared bolts.
Once you've undone about 10mm of bolt, you should be able to get some mole grips (or similar) on it to unscrew it fully.
It shouldn't be at all difficult with an M8 (which I think is what a crank arm bolt is).
-
EZ Out/ screw extractor is my choice for small diameter bolts like those used on HollowTech2 cranks.
-
Thanks both. Not used either of those. May try and pick up both, as probably useful to have. ACPs seem to be <£10. Any recommendations / particular set of EZ out extractor?
I have a very heavy vise - though not attached to anything - hopefully useful to hold crank arm.
-
It shouldn't be at all difficult with an M8 (which I think is what a crank arm bolt is).
Given it's an HTii arm, aren't these the pinch bolts tangential to the BB axle and more like M5?
-
Dunno which brand to buy as I used an inherited set. Success is almost entirely about how well/ straight you drill the frozen bolt and not bending the extractor while turning it.
-
If the bolt turns fairly easily, maybe glue a stick to it and turn the stick.
-
The bolt head sits in a counterbored hole and the other end of the bolt is recessed so it will be difficult to get at it with a centrepunch. If it is the outboard bolt that has failed then you should be able to remove the retaining pin thingy and you then have access to a couple of millimetres of the threaded portion of the bolt through the split that you pinch up with the bolts. I can get enough purchase on this to rotate the bolt using a pair of knives* although it would need to be pretty free running for this to work on yours.
*other bodges are available
-
The bolt head sits in a counterbored hole and the other end of the bolt is recessed so it will be difficult to get at it with a centrepunch. If it is the outboard bolt that has failed then you should be able to remove the retaining pin thingy and you then have access to a couple of millimetres of the threaded portion of the bolt through the split that you pinch up with the bolts. I can get enough purchase on this to rotate the bolt using a pair of knives* although it would need to be pretty free running for this to work on yours.
*other bodges are available
The flat end of the sheared bolt is 0.5-1mm proud of the shaped 'exit' recess, so it may be Ok to get an angle using a centre punch. Might try this for starters, while researching 'EZ out'extractors.
-
Left handed drill bit?
Might start to reverse it out. If it doesn't, at least you're starting the hole for the Eazy-Out.
-
It shouldn't be at all difficult with an M8 (which I think is what a crank arm bolt is).
Given it's an HTii arm, aren't these the pinch bolts tangential to the BB axle and more like M5?
My mistake, and you are quite correct.
I've managed to extract a 5mm (or it could've been a 4mm) sheared bolt from a saddle clamp using the ACP method.
The thing with using a stud extractor is that if you manage to snap that, you are giving yourself a headache in a completely different league.
Using the ACP method you are unlikely to create much collateral damage.
The bolt head sits in a counterbored hole and the other end of the bolt is recessed so it will be difficult to get at it with a centrepunch. If it is the outboard bolt that has failed then you should be able to remove the retaining pin thingy and you then have access to a couple of millimetres of the threaded portion of the bolt through the split that you pinch up with the bolts. I can get enough purchase on this to rotate the bolt using a pair of knives* although it would need to be pretty free running for this to work on yours.
*other bodges are available
You only need to target the ACP marginally off-centre of the bolt for this technique to work.
Obvs. targetting the ACP as close to the circumference is beneficial/efficient, but by no means essential.
It is deffo the low-risk variant.
ETA: I've recently acquired a 'Damaged Screw & Bolt Remover' set.
https://www.higomore.co.uk/products/damaged-screw-extractor-set-of-4?variant=158271020&gclid=Cj0KCQjwmIuDBhDXARIsAFITC_4tPeH5CAaSo6KO0oOjAPmgm-CGcVwqSmkRJMqhvpsdONxULe9b5koaAi9KEALw_wcB
I've yet to use it, but it strikes me as being a bit easier to deploy than drying to drill through the centre of a bolt to then counter-drill using an extractor.
-
If the crank is aluminium and thee bolt is steel, you could get all Zigzag on its donkey and dissolve the bolt out with a saturated alum soluti.
-
OK, I can make a good dent with the ACP fairly near the outer edge of the bolt end, and I can move the bolt around & out a bit (ACW out of the exit recess), then no more. Likewise really easy to move the bolt in ~3mm then it stops again. May need to try an easy out drill set.
-
I'm not exactly sure what you mean by "exit recess". Do you mean the opposite end to where the head was?
If the bolt has sheared then the thread will probably be stretched and you won't be able to turn the remnant of the bolt any further in. It has to go back out the way it came in.
When I had this problem I centre-punched the end and started drilling a 3mm(?)pilot hole. As I was doing this the bolt remnant started to turn and came out the way it went in. Maybe I was lucky, but it's worth a try before you invest in easy-outs and left-handed drill bits.
(This was on a secondhand Sugino crankset that had a M5 threaded bolt that appeared to be non-original and too low a grade. I replaced it with Grade 14.4 bolt. Sugino now use M6 threaded bolts on the latest versions of the same cranksets so I think it must have been a common problem. My Shimano Tiagra also uses M6 bolts.)
-
Thanks. I had pereservered with the ACP and managed to get the bolt to emerge from the opposite end to where the head was. I made a small dent in the side of the bolt and used the ACP to get just enough bolt out to get a mini pair of mole clamps side on, and turned the rest out bit by bit. Don't think I've damaged the thread, but it's a possibility I guess - the good bolt screws in OK to the thread in question. Will try and source some Shimano bolts and check how crank arm tightens on to HTII axle end. Hopefully that will be enough to tell. ETA I note that the bolts on this crank arm had no washers - which they should have, so perhaps also non-original.
-
As for how the arm attaches, use one of the plastic "bolts" to pre-load the bearing, then tighten the two clamp bolts (not forgetting to put the "hook" in place).
If it is a triple, there should be a large bevelled washer that goes between the NDS arm and the frame (to equalise the Q factor).