Seat Stem - Fixable?

Postby Rik on Wed 6/Jan/16 12:58pm

After many many Ks of service the bond on my seat stem has given up. Has anyone ever tried to re-bond these, if so, using what product? Epoxy?
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Re: Seat Stem - Fixable?

Postby AgrAde on Wed 6/Jan/16 1:08pm

Use this as an excuse to buy a nice Thomson or a dropper :D

If anything was to work, it would be a 2 pot epoxy. Loctite metal epoxy is boss, but expensive.
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Re: Seat Stem - Fixable?

Postby Simonius_Titius on Wed 6/Jan/16 1:28pm

Don't be tempted to drill & screw it too, that creates a weak point. Just glue.

Fast-curing epoxy is weaker than the standard slow stuff, was my impression. Be careful to get the ratio even, and mix very well. You can speed up curing in a warm oven.
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Re: Seat Stem - Fixable?

Postby Wobbler on Wed 6/Jan/16 1:44pm

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Re: Seat Stem - Fixable?

Postby Velocipedestrian on Wed 6/Jan/16 2:17pm

Really? How brave are you? (or how blase about your taint).

That gets a big "hell no" from me, and a second for a Thomson.
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Re: Seat Stem - Fixable?

Postby AgrAde on Wed 6/Jan/16 8:12pm

Velocipedestrian wrote:Really? How brave are you? (or how blase about your taint).

That gets a big "hell no" from me, and a second for a Thomson.


It's not like it's going to ping out all of a sudden and give you a surprise when you try sit down again. Any self-respecting mountain biker carries electrical tape with them, which would give you a perfectly functional seatpost to finish the ride on if it were to come loose.
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Re: Seat Stem - Fixable?

Postby Velocipedestrian on Wed 6/Jan/16 8:30pm

AgrAde wrote:
Velocipedestrian wrote:Really? How brave are you? (or how blase about your taint).

That gets a big "hell no" from me, and a second for a Thomson.


It's not like it's going to ping out all of a sudden and give you a surprise when you try sit down again. Any self-respecting mountain biker carries electrical tape with them, which would give you a perfectly functional seatpost to finish the ride on if it were to come loose.

I clearly have no self respect. But I do respect my taint.
Seatpost must be reliable.
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Re: Seat Stem - Fixable?

Postby Rik on Wed 6/Jan/16 9:44pm

AgrAde wrote:It's not like it's going to ping out all of a sudden and give you a surprise when you try sit down again. Any self-respecting mountain biker carries electrical tape with them, which would give you a perfectly functional seatpost to finish the ride on if it were to come loose.


This is exactly how the factory bond failed. it just got a tiny bit loose allowing the saddle to twist. It took 5 minutes whacking it with a ball peen hammer trying to drift it out. So I'd be pretty surprised (literally) if it just suddenly popped out.
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Re: Seat Stem - Fixable?

Postby pokey on Thu 7/Jan/16 12:24pm

Too bad you took it apart, I've have success with 290 wick in Loctite.

Simonius_Titius wrote:Be careful to get the ratio even, and mix very well. You can speed up curing in a warm oven.


High strength Araldite is probably cost effective. Curing is as important as quantities, it reaches the optimal claimed strength after 3 days and curing at 40ºC for 16 hours which is fairly standard for such adhesives in my limited bike shop boy experience.
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Re: Seat Stem - Fixable?

Postby Velocipedestrian on Thu 7/Jan/16 1:00pm

pokey wrote:Too bad you took it apart, I've have success with 290 wick in Loctite.

Simonius_Titius wrote:Be careful to get the ratio even, and mix very well. You can speed up curing in a warm oven.


High strength Araldite is probably cost effective. Curing is as important as quantities, it reaches the optimal claimed strength after 3 days and curing at 40ºC for 16 hours which is fairly standard for such adhesives in my limited bike shop boy experience.


Ooh, I guess far left, or second-to-far-right.
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Re: Seat Stem - Fixable?

Postby Kev on Thu 7/Jan/16 1:26pm

I reckon 3rd from the left. Bike shop boy is obviously a term of endearment
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Re: Seat Stem - Fixable?

Postby Rik on Thu 7/Jan/16 2:30pm

Trick question because you are infact the one taking the picture? :)
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Re: Seat Stem - Fixable?

Postby ape on Thu 7/Jan/16 6:10pm

A little bit of prep would be ideal.. scrape/chip off any obvious old glue, then sand lightly. Rough sandpaper is fine. I'd go with 80 grit or similar. all you're trying to do is rough up the surface a bit so the epoxy has something to bind to. While araldite will most likely do the job ok, a rubber toughened epoxy such as Adhesive technologies HPR5 or HPR10 would be ideal. These type of product is designed for gluing boat decks onto hulls or aluminium parts to composite parts. The rubber filler increases the toughness of the resin (reduces brittleness), improving resistance to peel/tear failure and forces due to differential expansion between the aluminium and composite materials.

Any decent composite workshop who work with epoxy resins (rather than poly/vinyl esters - chop-matt crap) should have a tub of an appropriate resin on hand, the amount you need would cost basically nothing. If you spend the price of a tube of araldite on beer, and show up at a shop at lunchtime, you'll get a better job done, and not have a tube of resin lying around not being used anyway. They should be able to tell you what's needed in the way of post-curing (heating) to gain full strength.
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Re: Seat Stem - Fixable?

Postby znomit on Thu 7/Jan/16 11:29pm

Rik wrote:Trick question because you are infact the one taking the picture? :)

Check his statz.
That thing has no seatpost.
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Re: Seat Stem - Fixable?

Postby AgrAde on Fri 8/Jan/16 1:17am

No but it's mostly constructed with trial and error, and glue ;)

If anyone knows what works and what doesn't, it's likely someone that worked on the Britten.
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