Re-tapping Campagnolo hidden bolt thread

[beercan]

So I goofed the installation with a set of chainring a it shouldn't have used on my centuar aluminum cranks, any advice or are the crank arm toast? The first few threads are a a bit crooked and the bolt is threading in at a slight angle, was hoping is a lbs would be able to correct my mistake

[beercan]

Also do I need the .4mm spacer for these cranks? Confused on what models need this spacer. Feel like a loaf of bread after finding out that the hidden bolt is slightly offset to 112

[ultraman6970]

If the crankset is 110 bcd you are not the 1st one that can't figure it out that if the bolt holes doesn't align when you present the chainring onto the crankset then you have to turn the chainring till they do align before just go and start bolting stuff up :D (rant just because is just me :D), Seen those more than a couple of times at my door step with the guys in tears. Expensive lesson. If 135 well... no comments :D

This is what you do because I had fixed that. Take the arm off the bike obviously, take the chainrings off the crankset... since the 1st two or 3 threads are wrong just use an old bolt from another set, usually those are made of steel (be sure the thread match 1st ok? just grab the back of one of the other bolts and test it)... and align that to perfection with the hole in the hidden arm, if you are careful and good at it you will engage the deeper threads and ready to go, back and forth to kind'a re do the bad threads and problem solved.

Another way because I have done it too, if the thread in that old steel bolt match... cut female side of the bolt in a half, then screw it in the bolt so you get like 2 or 3 threads showing up, then dremel that to make those 2 or 3 threads like conic (just a little bit).and unscrew the bolt back and forth till you can unscrew it and screw it cleanly, and no residues of material are floating around. Align the screw in the hidden bolt really carefully till you can screw it by hand all the way in, the idea is to make the good threads in the bolt to grab the good threads in the crank. Basically what are you doing is a chaser thing tool. Some times you need to force it a little bit but that bolt needs to get aligned perfectly or you could make the problem worse.

It is fixable tho, just be careful. About and lbs doing it, sincerely and because I do my own stuff I really doubt an lbs will even try, sure they will tell you to call campagnolo for a warranty or something (IMO is not a warranty problem, user problem).

Hope this helps :)

[oliver1850]

I would probably try to straighten the thread out using just the hidden bolt. Must be kept aligned with the hole in both planes when starting. If you can get it started straight, you may be able to get it to lead into the good threads cleanly.

If you can't salvage the threads, you might be able to find a Helicoil to fix it. I'm not sure what the threads on the hidden bolt are, but it's easily checked.

As to the shim behind the big ring: I don't think all hidden arm cranks have them. It doesn't show in the parts book for any crank I've seen, including 8 speed Record (which often had them), and is not included in the complete chainring bolt package. I believe that it was added when needed to compensate for machining tolerances. I would check the gap to the hidden arm pad with a feeler guage, with the ring bolted down at the other 4 arms.
I checked a few UT cranks of different groups - none appeared to have a shim but I didn't take them apart.

[buldogge]

Mark is correct...they were handchecked at the factory and shimmed as necessary. I've had cf cranksets with and without them. Feeler gauge as he said...shim as necessary.

As far as the threading...use a bottoming tap if possible.

-Mark in St. Louis

I would probably try to straighten the thread out using just the hidden bolt. Must be kept aligned with the hole in both planes when starting. If you can get it started straight, you may be able to get it to lead into the good threads cleanly.

If you can't salvage the threads, you might be able to find a Helicoil to fix it. I'm not sure what the threads on the hidden bolt are, but it's easily checked.

As to the shim behind the big ring: I don't think all hidden arm cranks have them. It doesn't show in the parts book for any crank I've seen, including 8 speed Record (which often had them), and is not included in the complete chainring bolt package. I believe that it was added when needed to compensate for machining tolerances. I would check the gap to the hidden arm pad with a feeler guage, with the ring bolted down at the other 4 arms.
I checked a few UT cranks of different groups - none appeared to have a shim but I didn't take them apart.

[Peter P.]

To correct an f'd up blind thread, you can purchase a couple different types of thread taps and use them in sequence.

First use a TAPERED tap to catch whatever threads are available to begin the thread cutting process. That's what it's designed for, as well as tapping through-holes.

You can next use a PLUG tap, which has fewer tapered cutting threads. It'll get you most of the way there.

Last, use a BOTTOMING tap, which is designed to cut right to the bottom of a blind hole. It only requires good threads at the start, which you've ensured by using the 2 taps above.

In some cases you can get away with using just one of the first two taps mentioned, depending on if the chosen tap cut deep enough to make the first 2-3 threads useable for the bottoming tap.