Drilling out a chainring bolt from an SRM

Discuss light weight issues concerning road bikes & parts.
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chase196126
Posts: 219
Joined: Sun Oct 12, 2008 11:11 pm

by chase196126

I have a little problem with some chainring bolts on my DuraAce SRM.

Basically the two little slots in the back of the chainring bolt have been stripped out by a previous owner and I cannot get purchase on them with either a screwdriver or the proper Shimano tool, so they simply spin in place when i try to unscrew them with an allen key.

I have been reading up on how to drill out the bolts in a situation like this, but I am nervous about the hardware that is in the SRM spider. Does anyone have some tips for what I should do to make sure I dont damage the SRM while drilling out the bolts? Other options for removing them are welcome as well.

I plan on having a professional do this with the proper tools as I dont have the equipment needed, or the experience.

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GZA
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by GZA

Well SRM cranks are usuable with a tab partially missing so if you do mess it up it will still work with no problems.

Tim
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by Tim

take the crank arm of the bike, put the allen key in the vice, put the crank arm 'on' the allen key (the chainring bolt you have problems with).

take a sharp screwdriver or such and a hammer and hammer on the nut non clock wise and it should come loose and the problem solved. Then replace the bolt & nuts with some new. I've done this several times. even thought I have the proper tools I avoid this style of chainring bolts, there is some available that suits an allen key on the nut as well (you use totally 2 allen keys), a much better solution imo.

whodesigns
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by whodesigns

I would NOT recommend striking your SRM with a hammer in any way. It would be quite simple to drill out the bolt, the standard ones that come with the crank are Aluminium alloy so are easy to drill. Use a 8mm drill bit or similar size, don't go bigger than 10mm as that is the size of the hole in the crank.
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Ypsylon
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by Ypsylon

Have you tried some WD-40 and tilting the allen wrench a bit while turning?

If the outside part of the nut is allready spinning freely I don't think there can really be significant clamping forces, so it's more the friction of the threads against each other, which you can reduce with the WD-40.

If you push the allen wrench to one side you are pressing the nut against the chainring/spider and you might be able to stop it from turning. Thinking about it, you might wanna try this before applying WD-40.

You can try'n squeeze the chainring together in the location of the bolt and press the nut up with your finger and try to turn the allen wrench really slowly.
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Gregorio
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by Gregorio

Try "Easyout"
http://www.amazon.com/gp/product/B0002U ... MVVBVVB41E

you can find them at any hardware store

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GZA
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Location: Chilterns, England

by GZA

There is nothing easy about an easy out! They promise so much but deliver so little usually

chase196126
Posts: 219
Joined: Sun Oct 12, 2008 11:11 pm

by chase196126

Thanks for all the suggestions guys!

I tried putting the allen in at an angle, but i still cant get any friction between the bolt and the ring. I sprayed some WD40 on them and let them sit over night, but no luck there either.

I think ill just have to take this one to a machine shop.

Gregorio
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by Gregorio

GZA wrote:There is nothing easy about an easy out! They promise so much but deliver so little usually


I have tried to use it 3x and had success all 3x. Maybe I am lucky or maybe you had a case of operator error

11.4
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Joined: Tue May 23, 2006 4:33 am

by 11.4

To add to your responses so far:

1. Definitely don't hammer in any way on an SRM. You can at least mess up the calibration of the strain gauges, if not break something inside or outside.

2. I don't really recommend any of the suggestions here, either because they are dangerous or they just don't work.

3. I hate to say it, but the way to protect a $3000 crankarm is basically to pay the bills to send it to SRM (it's off-season anyway, right?) and have them pull it. That way, any damage is warrantied. Machinists don't necessarily understand that there are fragile innards in an SRM powermeter, plus it's difficult without a lot of fixturing to hold the crankarm and spider immobile so you can drill it out under a drill press. SRM already has that fixturing so if it's done properly, it'll likely be cheaper done by SRM.

chase196126
Posts: 219
Joined: Sun Oct 12, 2008 11:11 pm

by chase196126

*Update

I got the bolts out! I took another close look at the bolts and realized that I could use a pretty narrow drill bit and slowly work away at the inside of the soft aluminium bolts. It took a little while of careful drilling but I was able to simply remove the threads of the bolt and it dropped right out of the rings. The nut was thick enough that I didnt even come close to the SRM spider with the drill.

I made sure to go gently and any vibrations or shaking the SRM experienced was much less than an average day out on chipseal.

Thanks for all the suggestions everyone! I really appreciate the help :beerchug:

Geoff
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Location: Canada

by Geoff

When you re-install the chainring bolts, use a copper-based anti-seize compound, not grease, on those bolts and you will never have that problem again...

11.4
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by 11.4

Geoff wrote:When you re-install the chainring bolts, use a copper-based anti-seize compound, not grease, on those bolts and you will never have that problem again...


Definitely +1. Most people install these dry, and frozen chainring bolts are sadly too common as a result. Trackies who are removing them several times a day either avoid the problem simply because they are removing them all the time (and they never get a chance to freeze up) or (if they are good trackies) by putting a little antiseize on the bolts. It doesn't need much at all so it doesn't have to be a mess.

Of course, it takes the brilliance of the average trackie to understand such subtle points about bike equipment.

Geoff
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by Geoff

Hah! Guess where I learned that 20 years ago!

chase196126
Posts: 219
Joined: Sun Oct 12, 2008 11:11 pm

by chase196126

Thanks for the tip guys, I actually had some anti seize ready to go right after I got the bolts off :mrgreen:

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