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Tap stripped fender mount?

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Tap stripped fender mount?

Old 03-20-08, 09:37 PM
  #1  
Mark Turner
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Tap stripped fender mount?

I screwed up and cross-threaded a bolt while mounting a fender on my brand-new bike (Novara Randonee) today. The 5mm x 0.8mm bolt now won't screw in at all (I tried and broke one off, which I removed with vicegrips). Is the solution to tap the hole? Can it be rethreaded same size? Will I need an alignment jig to get it straight? The hole is in the short tube between the seat stays.
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Old 03-20-08, 09:44 PM
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It's definitely worth a try to simply re-tap. Since it doesn't need a huge amount of strength, the threads should be fine, just be careful while tapping and it will probably work.

Worst case, you have to drill and tap to M6 and work around it with your fenders.
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Old 03-20-08, 09:55 PM
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The stock size is a 5.0 x 0.8 mm metric tap. If you didn't force the screw in all the way then you likely just messed up the first couple of threads. When you use your tap to try to clean it up try to feel for the original thread and follow that so you don't do more damage.

If worst comes to worse then I second anti.team's suggestion to drill it out a little more and use the other universal bicycle size thread 6.0 x 1.0 metric. Don't just force it in though. Drill out the the braze on with the correct size drill first and then tap it other wise it'll mess up and not cut. Taps are not drill bits.

Best of luck with the repair.
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Old 03-20-08, 10:17 PM
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If it is possible to start the tap from the 'back side', the side opposite where you would start the screw, you should be able to feel the tap pick up the original, straight, undamaged threads. Go slowly . . . proceed all the way thru. Visually check the squareness of the tap as you begin.

As another poster mentioned . . . there will probably be enough threads left to do the job.
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Old 03-21-08, 05:51 AM
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Originally Posted by dwood View Post
If it is possible to start the tap from the 'back side', the side opposite where you would start the screw, you should be able to feel the tap pick up the original, straight, undamaged threads. Go slowly . . . proceed all the way thru. Visually check the squareness of the tap as you begin.
Yup, that's important.
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Old 03-21-08, 11:11 AM
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A big shiney red Estar for you dwood... That's an excellent idea if it's one of the tubular surface mounted braseons.

To the OP. Once you get this thing cleaned out forever after use some extra care when starting the screw. Even after it's cleaned up there will be remains of that other path and the screw will sometimes try to take the fork in the road instead of the right way. Just run it in with your fingers until you're SURE it's on the right thread.
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Old 03-21-08, 12:21 PM
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Well, if you can't fix the threads with an M5 tap, I'd just drill the thread out.

Instead of re-tapping, you could put a button head, M5 bolt into the hole, inside out, then your fender strut, washer, then a nyloc nut.

I do this all the time on frames that don't have threaded eyelets.

John
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Old 03-21-08, 01:57 PM
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Originally Posted by dwood View Post
If it is possible to start the tap from the 'back side', the side opposite where you would start the screw, you should be able to feel the tap pick up the original, straight, undamaged threads. Go slowly . . . proceed all the way thru. Visually check the squareness of the tap as you begin.

As another poster mentioned . . . there will probably be enough threads left to do the job.
I was going to suggest this too. But first, instead of using a tap from the back, just use a long screw. If possible, screw it all the way through. It may fix the threads without doing any cutting and metal removal..put a tab of grease on first.. If the screw seems unreasonably tight when you try it, use a tap as backup plan.
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Old 03-24-08, 05:33 PM
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Originally Posted by BCRider View Post
To the OP. Once you get this thing cleaned out forever after use some extra care when starting the screw. Even after it's cleaned up there will be remains of that other path and the screw will sometimes try to take the fork in the road instead of the right way. Just run it in with your fingers until you're SURE it's on the right thread.
Thanks to all for your suggestions. I picked up a M5 tap this afternoon and was able to restore the threads from the front side. There was no rear access. I had to use the tap a 1/4-turn at a time because the handle was too long to go between the chainstays, which caused a minor panic until I figured out I could put the handle on loose and reposition it often. New skill learned, and now my fender doesn't rattle.
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Old 03-24-08, 06:02 PM
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Originally Posted by mcmurryjohn View Post
Well, if you can't fix the threads with an M5 tap, I'd just drill the thread out.

Instead of re-tapping, you could put a button head, M5 bolt into the hole, inside out, then your fender strut, washer, then a nyloc nut.

I do this all the time on frames that don't have threaded eyelets.

John
Doesn't it protrude inside the chainstay/axle area if you do this though? Or is button head nearly or very close to flush against the dropout?
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Old 03-24-08, 08:34 PM
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Just watch how much you tighten that side since the threads will not be the usual full depth now after all the cross threading and re-tapping. Proper torque for a 5mm bolt is only two fingers held close to the bend on a hex key and torqued so that you don't quite hurt the fingers anyway. If you remember that you'll likely never have any issues.
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Old 03-24-08, 09:43 PM
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Originally Posted by BCRider View Post
Just watch how much you tighten that side since the threads will not be the usual full depth now after all the cross threading and re-tapping. Proper torque for a 5mm bolt is only two fingers held close to the bend on a hex key and torqued so that you don't quite hurt the fingers anyway. If you remember that you'll likely never have any issues.
No torque wrench, but I didn't tighten the bolt too tight. A little low-strength loc-tight clone should help keep it from vibrating out.
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