mzeffex 

Not the bolt that's stripped, but the part in the crank arm itself that the bolt goes into. The small ring on a Shimano SLX crank. Can these be retapped? It does NOT go through all the way - so you could not run a tap all the way through.

If not.. is it fine to run the small ring with 3/4 bolts?

I was putting it back on like an idiot and did this. New crank too.

cnnrmccloskey

Not sure if they can be tapped but I would assume so.
It is not safe to run with 3/4 bolts at best it will become extreamly out of true and at worst i've seen older chainrings bent to a 90 degree angle and slam into the chainstay under high torque because it was without a bolt and that was a 5 bolt which obviously is a stronger design, Not to say this will happen to you but it has happened before

Sixty Fiver

Theoretically - You could drill and re-tap it to a larger thread size, use a larger bolt, and would have to drill the chain ring to match.

mzeffex 

Crap. Thanks.

FBinNY 

The crank might be saved if you didn't force the bolt on too far. If there are still good threads beyond the damaged zone, a skilled mechanic might be able to re-establish a good lead and pick up the original thread. It's a bit of a skill job because the tap will tend to pick up the false lead of the cross thread, but it's worth a shot.

Other options include using a helicoil insert if one exists in that thread, or possibly building up the hole with one of the "plastic metal" products and re-taping it.

Given that it's a new and pricey crank arm, I'd go the extra mile in trying to save it. And BTW- no you can't run with only 3 of 4 bolts.

ryanwood

I am relatively new to wrenching my bikes, but I have drilled and tapped plenty of bolt holes on engine blocks, steel and aluminum, so I don't see any reason why you couldn't do it with a crank. The only problem I could see is maybe running out of room, or removing too much material and compromising the strength of the crank.

San Rensho 

See if you can start a bolt throught the REAR of the threads. If so, ust the bolt as a tap, lube with WD40, turn it a qarter turn, back off, another quater turn, etc, removing the bolt occasianlly and cleaning all the removed metal and starting again. Go slow.

davidad

The third ring holes are blind.

davidad

Find an 8mmX.8 bottom tap and see if you can retap it. Go slow at first to get it aligned.

mzeffex 

Doesn't go through all the way

joejack951

Your best bet is FBinNY's suggestion. The tap should be an M8x1mm (not the more common M8x1.25mm). With a proper setup, getting the tap started using the original lead-in should not be much of a problem. If you are not experienced with using taps, don't even bother trying. Give the crank to someone who knows what they are doing. As long as you did not completely mash the original threads, what's left should be plenty strong. You could also use a slightly longer chainring bolt (maybe 2-3mm) to try and engage some previously unused threads at the bottom of the hole.

HillRider

I don't think that's right, I believe davidad's recommendation of an M8x0.8 mm tap is correct.

All of the chainring bolts I tried will not thread into a bolted bottom bracket spindle which I know for certain is M8x1.0 and I'm equally sure chainring bolts are NOT the very common M8x1.25 mm.

JohnDThompson 

I suspect you could shoot a helicoil into it to fix it.

joejack951

My bad, but it's also not M8 x 0.8. It looks like it should be a M8 x 0.75. This tap would do the trick for making more threads if needed (though at this price you might want to find an LBS that owns the tap already):
https://www.mcmaster.com/#26015a173/=5mrp76

You'll want to start out with a tapered tap though to get things aligned properly first.

Sixty Fiver

You will still need to drill and re-tap the crank to accept a helicoil... it's doable by anyone with decent mechanical skills.

Helicoils come in pretty much any size you might need and a kit will let you know what size of drill to use to prepare the hole for threading although the drill bits are not included.

Drilling and tapping aluminium is fairly easy because it is a softer metal but also increases the risk of screwing things up... the helicoil will increase the strength of the repaired area.

So factor in the cost of the helicoil, drill bit you will need, and time (if you have to pay someone to do it) and see how this compares to the cost of replacing the crank.

mzeffex 

Wow, my friend said he knew how to fix it. Give it to him, 20 minutes later I have my crank with the bolt all the way in at an angle. The chainrings on tight though.. so I guess it's okay to ride?

LarDasse74

I am afraid it is definitely time for a replacement.

The crank is probably repairable, but get a new friend.

mzeffex 

FBinNY 

It's probably fine to ride, and with luck you'll forget about the issue until it's time to replace the granny.

In my earlier post I said it took a bit of skill to pick up the correct lead and tap it properly. Apparently your friend, lacked that skill, and either forced a tap extending the thread slightly, or trimmed the bolt and jammed it in, possibly with some threadlocker. Either is probably OK for now, but not very workmanlike. In any case I wouldn't take it apart to check, since there might not be much meat left to work with.

If you can't live with it this way, or if it lets go PM me and I'll hook you up with a proper job, probably using an insert.

mzeffex 

Retapped