SpasticSprocket

I've got a couple of loose brazes on my 1985 Cannondale touring bike, one on the seatstay and one on the seat tube. I was hoping someone might know what could be wrong and if it could be fixed without too much effort.

FBinNY 

Even though we call them braze-ons, based on how steel frames are made, these are actually riveted on. Maybe we should start calling them rivet-ons, since that's how bosses are usually attached to aluminum and carbon frames.

Anyway, the solution depends on how loose they are, and whether the tube or the hole is deformed or not. The braze-on is actually a riv-nut attached as shown in the video here.

If it's only slightly loose and the hole and tube are OK it will probably tighten once the screw is attached and tightened. If they spin making it hard to tighten so a drop of super glue will solve that and the water bottle screws will keep them in place.

If they're very loose, stripped, or the hole is enlarged, the best bet is to drill them out and set new ones after dealing with the tube damage. This can be more complicated, so you might want to let the local shop take a look and advise you.

mechBgon

edit: yeah, what he said ^


They're riv-nuts and can be snugged up. The appropriate tool is the best way to approach this; they function like a rivetting tool. This is the kind I have, a Marson:



A well-equipped LBS will probably have one and could snug up your riv-nuts for a fee, or even remove and replace them.

SpasticSprocket

Thanks for the quick responses I was a bit worried that it might require something more than a special tool. I'll ask around at the shops and see if anyone has one of these tighteners.

FBinNY 

As I said, simply mounting and tightening the water bottle screw will clinch the nut.

If it's free-spinning, but otherwise OK, you don't need a shop or special tool. Go the the hardware store and buy a long 4x.8 metric cap screw (must be a high strenght cap screw or CrMo hex head screw) a nut and a few washers.

Thread the nut and washers onto the cap screw, Then thread it fully through the loose riv-nut. Now hold the screw and tighten the nut down against the frame. This will draw the nut portion up, while the washers hold the head down and compress the fitting. It doesn't take a great amount of force, so don't get carried away and snap the screw, and have to come back here and post "how to remove a broken..."

SpasticSprocket

Awesome. I've got a hardware store five minutes from my house so I'll go check that out, thanks for the DIY fix instructions.

FBinNY 

I forgot to add the word fully where I said thread the screw in. Make sure it's threaded fully through the riv-nut, and not hanging by a few threads. You don't want to strip it.

SpasticSprocket

So I should just thread it in until there's no more visible thread with the nut and washers all the way up to the cap?

FBinNY 

That doesn't matter either way. Just make sure to thread in at least 6 or seven turns through the nut so there's more than enough thread engagement. I see enough threads here where people strip crank arms by having the extractor engaged on only 2-3 threads, so I felt the need to remind you not to do something similar.

fietsbob

I have expanded them in situ, by using a thick flat washer, or a few,
and a strong hex head bolt, grease the bolt threads..
1/4" drive ratchet and a 8mm socket are nice.
box end wrench if no room..
you are pulling the threads, against the outside shoulder of the riv-nut,

and expanding the piece in the process

mechB those non rotating riv-nut tools are different,
I have the grab the pin and pull tool for regular poprivets.

jsharr

Check out this blog from Park Tool. Fix that loose riv nut with a quick release axle and skewer.

https://www.parktool.com/blog/repair-...ottle-fittings

davidad

This is the way I have done it. Works fine.

HillRider

One minor correction, the proper bolt size is an M5x.8, not an M4.

Homebrew01

I've used the FBinNY method. I have not tried the QR method but that should work too. I would think it would be a bit harder to go by "feel" with the QR method though.

SpasticSprocket

I've been trying FBinNY's method but I can't get the darn thing to actually apply pressure and pull the fastener in to expand it.. anyone think trying a hex head bolt with a ratchetike what was suggested would work better? Or OS it likely I've completely stripped it?

jsharr

did you get M4 or M5? As others have noted, water bottle fittings are usually M5.

SpasticSprocket

I used M5 I noticed that M4 x .8 didn't exist..

jsharr

If you are holding the bolt from turning and backing the nut off the bolt with a wrench, the rivnut should be getting tightened up as you force the nut against the washer and thus against the rivnut.

It will not work if you are allowing the bolt to turn.

If the threads in the rivnut are stripped, as you back the nut off and force it against the washer, you will be pulling the bolt out of the rivnut. Seems like you would feel the bolt slipping if this was happening.

SpasticSprocket

I did it the way you described.. and I don't feel the bolt slipping.. it just seems like the nut won't quite tighten.. I think I might've stripped somehing though because once when I tried it I heard a sort of snap.

Homebrew01

Post a picture of your set up

SpasticSprocket

That will have to wait a few hours as I'm currently working.

mechBgon

By a weird coincidence, I had to bust out my Marson today and redo FOUR loose riv-nuts (on a brand-new Trek Madone, no less). Sunspots...?

SpasticSprocket

Well I think I may have stripped one.. How expensive can having this stuff drilled out and replaced get?

mechBgon

If it's on the downtube, getting the drilled-out riv-nut out of the frame will require removing either the fork or the bottom bracket, so that would put you into an overhaul of one or the other, which is probably around $20 labor for the overhaul, plus $15-$20 for the riv-nut job itself (high risk factor, specialty tools).

SpasticSprocket

It's actually on the seattube so I'd imagine you just pull the seatpost out?