Author Topic: Taps & dies for bike bolt hole repair  (Read 1681 times)

BrianI

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Taps & dies for bike bolt hole repair
« on: July 16, 2016, 07:24:04 pm »
Looks like I've stripped the lower bolt bosses on my decathlon mtbso, for fixing the pannier rack.  Looking on am@zon, there seems to be various tap & die sets, from £6.99 for a 20 piece set up to well over £1,000.

I'm assuming the 20 piece set for £6.99 would be made of cheese, but may be OK for repairing threads on an aluminium framed bike?  Any other suggestions? What should I be looking for in a tap / die set for occasional use?    The rack has the option of using an adaptor to mount using the rear wheel q/r. However doing that the cable disc brake caliper fouls with the rack arms...

Re: Taps & dies for bike bolt hole repair
« Reply #1 on: July 16, 2016, 07:29:54 pm »
M5 is about the only standard metric tap on bicycles - I'd just get one and a tap older of some sort...


...or get someone who has the tools to do it for you.
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Re: Taps & dies for bike bolt hole repair
« Reply #2 on: July 16, 2016, 07:33:30 pm »
It might be easier to use a longer bolt and a nut, if the boss can take it.

The thing to watch for with taps is they are very hard and very brittle, use lots of thin oil, go slowly and don't force it.

I can't comment on any particular taps but alu is quite soft and it should be a lot easier to work on than steel. You might have go the next size up if the boss is really stripped.

BrianI

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Re: Taps & dies for bike bolt hole repair
« Reply #3 on: July 16, 2016, 07:37:44 pm »
It might be easier to use a longer bolt and a nut, if the boss can take it.

The thing to watch for with taps is they are very hard and very brittle, use lots of thin oil, go slowly and don't force it.

I can't comment on any particular taps but alu is quite soft and it should be a lot easier to work on than steel. You might have go the next size up if the boss is really stripped.

A longer bolt and nut would work, except for the cassette in the way...  Mind you, the rack was only for supporting a rack pack. So perhaps a seat post rack might be the easiest solution, as I found that the rack got in the way if I had to adjust the rear cable disc brake....

Re: Taps & dies for bike bolt hole repair
« Reply #4 on: July 16, 2016, 07:47:26 pm »
why not just fit a rack that uses the QR skewer as the lower mount? Has to be stronger than a seatpost one.

cheers

Kim

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Re: Taps & dies for bike bolt hole repair
« Reply #5 on: July 16, 2016, 10:11:09 pm »
M5 is about the only standard metric tap on bicycles

And M6, for when the M5 threads get stripped.
Careful, Kim. Your sarcasm's showing...

Kim

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Re: Taps & dies for bike bolt hole repair
« Reply #6 on: July 16, 2016, 10:15:14 pm »
why not just fit a rack that uses the QR skewer as the lower mount?

Because the thing that you naturally want to use to lift the bike by becomes annoyingly floppy when you remove the wheel?  Sure it's still better than a seatpost one, but if there are proper mount holes it's going to be far better to use those.

I've got a mostly-stripped thread on a rack mounting hole on my Dawes.  Fortunately there was plenty of room, so I just drilled it out and put a nylock nut on the other side.  You may be able to get away with similar tactics using a pan-head screw inserted from the inside of the drop-out.
Careful, Kim. Your sarcasm's showing...

BrianI

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Re: Taps & dies for bike bolt hole repair
« Reply #7 on: July 16, 2016, 11:08:23 pm »
why not just fit a rack that uses the QR skewer as the lower mount? Has to be stronger than a seatpost one

cheers

My current rack has that option except fitting it that way means the rack arms foul the cable disc brake caliper...

Re: Taps & dies for bike bolt hole repair
« Reply #8 on: July 16, 2016, 11:18:54 pm »
a little bracket manufacture/modification could cure that?

If you have vertical dropouts I daresay the left side of the QR could be safely  spaced off with washers, might that give enough clearance for the rack?

-just a thought...

cheers

Re: Taps & dies for bike bolt hole repair
« Reply #9 on: July 17, 2016, 12:22:14 am »
I've got a tap'n'die set from Aldidl - probably cost under a tenner, lives in a nice metal box, and has done me fine for several years apart from snapping the M5 tap through cack-handedness (now replaced with a single tap from, IIRC, B&Q).

For light use, anything that's not made of obvious cheese will be adequate. As torslanda and Kim say, the most useful taps for bike use are going to be M5 and (especially for you just now) M6 - the advantage of a set over individual ones is that you'll get both of these, and a holder. If you have stripped the boss, I'd run a 5mm drill through it, and then retap to M6 - once you've got the kit, it's a ten minute job at most.

As hubner says, take it gently and lubricate generously - WD40 or GT85 aren't exactly approved tapping lubes, but they'll work fine for this sort of job. Half a turn max at a time - less if you're getting a lot of resistance - then back off quarter of a turn, and make damn sure the tap is going in square - if it's off-line, it's more likely to snap.


robgul

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Re: Taps & dies for bike bolt hole repair
« Reply #11 on: July 17, 2016, 09:42:29 am »
It might be easier to use a longer bolt and a nut, if the boss can take it.

The thing to watch for with taps is they are very hard and very brittle, use lots of thin oil, go slowly and don't force it.

I can't comment on any particular taps but alu is quite soft and it should be a lot easier to work on than steel. You might have go the next size up if the boss is really stripped.

A longer bolt and nut would work, except for the cassette in the way...  Mind you, the rack was only for supporting a rack pack. So perhaps a seat post rack might be the easiest solution, as I found that the rack got in the way if I had to adjust the rear cable disc brake....

The longer bolt idea is the simplest and cheapest solution - BUT feed the bolt through from the INSIDE of the dropout (i.e. put the nut on the OUTSIDE of the rack leg) - there's normally enough clearance with the cassette ... but if necessary source a bolt with a shallow head OR there are Philips bolts/screws that have a thin head (I just bought some from Screwfix yesterday)

... and for simplicity on my ancient Galaxy I have used bolts from the inside of the dropouts (front and back) with a thin normal nut on the outside of the dropout to hold it in position - then fitted the mudguard stays and/or rack leg, with a aeronut on the outside.  Works a treat - creating a "stud" and making quick removal of the rack or stays easy.  Subject to the bolt length, carefully cut off any protruding bolt on the outside of the aeronut for a tidy finish.

Rob

Re: Taps & dies for bike bolt hole repair
« Reply #12 on: July 17, 2016, 11:02:41 am »
What robgul said.

I'd had to do this load of times. File some flats on the sides of the bolt head (assuming you are using a screw-headed bolt), then you can grip it with needle nose pliers to stop it rotating when you tighten up the nut on the outside.
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robgul

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Re: Taps & dies for bike bolt hole repair
« Reply #13 on: July 17, 2016, 01:52:33 pm »
What robgul said.

I'd had to do this load of times. File some flats on the sides of the bolt head (assuming you are using a screw-headed bolt), then you can grip it with needle nose pliers to stop it rotating when you tighten up the nut on the outside.

 :thumbsup: - I've just spent the last hour or so fettling my pub/shopping bike and have fitted a rack using the "reverse bolt" method - I did grind down the head on the cassette side bolt to make sure clearance was OK

Rob

BrianI

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Re: Taps & dies for bike bolt hole repair
« Reply #14 on: July 17, 2016, 09:12:08 pm »
Had a look at it this evening.  I have plenty of clearance to do put the bolt head on the inside, assuming I use the upper bosses.  But then I need ~ 3/4" spacer for the rack arms to clear the cable disc caliper.  But this would then foul the mounts for the skiddii single wheel trailer....  (not that I'm planning on using it with the mtb, but at least it'd be good to have the option)  Unfortunately I also managed to strip out the seat stay rack bosses too - Decathlon mtbso must use pretty soft cheese for their threaded bolt holes.... If I used the lower bosses, there is just about 2mm clearance between the chain & the chainstay, so no room for a thin bolt  head.....   ::-)

So it looks like for the East Lothain Rough Stuff Audax next weekend, I'll transfer the Carradice SuperC seatpack from the roadie/audax bike onto the mtb for a bit of extra storage for munchies!   :thumbsup:   




Re: Taps & dies for bike bolt hole repair
« Reply #15 on: July 17, 2016, 09:20:35 pm »
a bolt head that is about 1.5mm thick is 'thick enough' I'd have said. If you fit the nut and long bolt (with Loctite) and then file/grind the head down you can make it fit OK. 

Once a long bolt plus nut is fitted thus you generally don't need to disturb it for months, years at a time (as per a post above).

If you upper mounts are nutserts, let into the stays, they can be drilled out and renewed.  If the threads are not quite fully stripped, you can often make them work OK by bonding a stud into the thread using epoxy resin.

cheers

robgul

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Re: Taps & dies for bike bolt hole repair
« Reply #16 on: July 17, 2016, 09:23:28 pm »
Had a look at it this evening.  I have plenty of clearance to do put the bolt head on the inside, assuming I use the upper bosses.  But then I need ~ 3/4" spacer for the rack arms to clear the cable disc caliper.  But this would then foul the mounts for the skiddii single wheel trailer....  (not that I'm planning on using it with the mtb, but at least it'd be good to have the option)  Unfortunately I also managed to strip out the seat stay rack bosses too - Decathlon mtbso must use pretty soft cheese for their threaded bolt holes.... If I used the lower bosses, there is just about 2mm clearance between the chain & the chainstay, so no room for a thin bolt  head.....   ::-)

So it looks like for the East Lothain Rough Stuff Audax next weekend, I'll transfer the Carradice SuperC seatpack from the roadie/audax bike onto the mtb for a bit of extra storage for munchies!   :thumbsup:

Firstly, to try and re-tap threads is tricky (as suggested) and success is very doubtful - however, depending on the rack (and its value/future possible use) it might be possible to cut the rack legs down, flatten/grind the ends and drill them to enable the use of p-clips a bit higher up the seat stays and clear the caliper and other stuff .... ?     

[My fettling today used p-clips for the top fixings on the rack/seat stays as there are no bosses on the c1982 531 frame]

Another option for the stripped top bosses, depending on the thickness of the stays, is to drill them out and fit Rivnuts (Google if you don't know what the are!)

Rob

PS - presumably the rear wheel has a QR? ... if it's nutted it would probably be possible to slip a couple of washers as spacers over the axle inside the dropout (springing the frame very slightly) to get clearance for a thin bolt-head.

Torslanda

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Re: Taps & dies for bike bolt hole repair
« Reply #17 on: July 18, 2016, 08:01:38 am »
Not, IME, if you have a disc brake...
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Taps & dies for bike bolt hole repair
« Reply #18 on: July 18, 2016, 01:48:58 pm »
The cost would be more than the bike's worth but no-one has yet suggested helicoiling which would be my choice if I had the kit (or access to it). I have never been very impressed however with the idea of hanging a rack off aluminium fork-ends. A P-clip could very well end up being a stronger option. Those mounts on the fork-end are in my opinion good for nothing heavier than a mudguard.

Putting my money where my mouth is I only have a saddlebag with a home-made bag support using the upper rack points and the seat-stay bridge on my mtbso.

frankly frankie

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Re: Taps & dies for bike bolt hole repair
« Reply #19 on: July 18, 2016, 02:25:33 pm »
For the top mounts a seat pin clamp - this sort of thing - may be neater than P-clips.
https://www.sjscycles.co.uk/seat-posts/286-axiom-trekk-seat-clamp-with-rack-mounts/
Something similar is also available from Decathlon - m-part branded.

I've never had any trouble with touring loads on alu or carbon frames where fork-end eyes are fitted - though I agree they often don't look substantial enough.  On dropouts with no eyes there's often enough flat metal to drill and tap a hole, I've done that on carbon frames, along with the seat pin clamp as above.
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