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Brake Mount Threads


Nick Manning

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I have had a look on the forum and various things about doing a helicoil, but i'm still clueless and not entirely sure if it will work with issue.

My problem is on the non drive side 4 blot mount the bottom thread has been damaged. Recently when taking the bolt out it pulled some of the thread out of the top, the rest of the thread is fine, but I have had to run a longer bolt to be able bite whats left of the thread.

Would a helicoil work on this and would it be recommended? Ifso, does anyone have a clue of what I need to do it and where to get it. Previous times when I worked for Halfords I just used a tap and die set and put a larger bolt in which sufficed. But I would like to try and keep it the same and not make it bigger.

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In one word. Yes :)

You can buy a helicoil kit for about 15 quid which will contain about 20 inserts so you can do it at home for free; alternatively take the frame to a friendly local engineers and they may be able to put one in for the price of a couple of beers.

Most decent tool/bearing shops should be able to get you a kit if they dont stock them, you will need a drill and preferably some oil to use as a tapping lubricant.

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Helicoiling is just tapping a larger thread (like you've done before) then dropping an insert into it to restore the original size thread again. If you've tapped threads before helicoiling is a breeze, if you haven't it's still easy!

You can grab yourself a kit for about £15 as has been said, or pop by a nearby garage/engineering firm and 99% of them should be able to help for next to nothing, it's a 2 minute job :)

I borrowed a kit of Jon Mack a while back, as did Mr Pearson. I stocked it full of inserts before sending it back, so drop him a line perhaps and you could get it done for the price of posting the kit (about a pound each way!)

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Depending on how much thread you pulled out, it would be better to use a slightly longer bolt if possible. The thread inserts are only about 5mm long, so if you were to helicoil the mount you would only be able to put 5mm of new thread in, unless you can get longer thread inserts (which I'm not sure if you can).

I have helicoiled 1 bolt hole on my old frame and all 4 on my friends frame, all which I only tapped to about 5mm deep as they all the holes had some thread left at the bottom.

Helicoiling is easy, just follow the instructions and you'll be fine.

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I read somewhere that Rich had used Jon's. Yeah I re-threaded one before but only to a larger size, but sounds fairly simple. Might try the local garage, or give Jon a pm, though I wouldn't mind purchasing a kit, has it seems pretty handle to have about. Any idea where I might be able to get one from Luke? Also what is the sizing I need, as I've looked on ebay and found quite a few but they all mention sizes.

Well my thread is only damaged at the top, the rest of it down to the bottom is screwing fine.

Edited by Nick Manning
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eBay generally have a few about, I'll have a look in a minute for you.

Standard maggie mounts are M5x0.8mm thread, and the kits are generally classified by the internal thread (ie. what you want to match the bolt), occasionally they'll be something like "M5 x 1D" or similar, meaning that they're an M5 thread, and the insert is 1 diameter long (about 5mm, in this case)

edit; beaten to it!

A 'coiled thread in alu is stronger than the original tapped thread, as a rule. Steel inserts are less likely to strip, so 5mm or so is plenty enough to hold a magura in place. If you were worried about there not being enough, and had room, you could always drop another insert on the top to double the thread area, though make sure you leave room to remove the tang or you'll have issues

edit 2; Nick, that's spot on (Y)

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Tang? lol You've confused me again.

Cool

If you look at the bottom of the insert, there's a bit of the coil which goes flat across the bottom. That's the tang. It's used to give something to grab hold of to screw in the insert, then snapped off once done so as not to get in the way of the bolt :)

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You probably need to buy a tap wrench seperately to use the tap if you haven't already got one, that's the only thing missing from the kits.

like this?

If you look at the bottom of the insert, there's a bit of the coil which goes flat across the bottom. That's the tang. It's used to give something to grab hold of to screw in the insert, then snapped off once done so as not to get in the way of the bolt :)

I see, makes sense.

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Tarty do a helicoil, its 15 quid for all four bolts.

I only need the one ehich is £4.89, but then I still have to strip my bike and send it to tarty and get it sent back.

Nick i got the lot.......drill bit tap and coil kit....il happily do it for you (Y)

Dave...

just send me a pm....its as simple as rooling a bifter :P

Cheers Dave, as your living so close I think I'l take you up on that offer. Are yuou about this weekend?

Rich still has mine, so if you give him a PM he might be able to send it on over to you :P

Cheer's Jon, I'm gonna see Dave and get it done there, but thanks for the offer.

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