Seat post- Repair it or trash it?

[bgoetz]

Well I a couple of weeks ago I came off of the rollers and broke my seat post in two /img/vbsmilies/smilies/redface.gif. I decided to shop ebay and found one that I purchased, but when I received it I could tell that the end that holds the seat had been glued and was out of alignment. I put it on and sure enough with a little twist it came loose. I ended up with a partial refund from the seller (best I could do) and used an epoxy to fix it. I feel like I did a good job and used a good epoxy and my thought is with as far down the post as it goes and the fact that the only way it would come loose again is a significant twist of the seat and then a pull upwards not much could happen safety wise. It is a carbon/aluminum post.

I felt pretty good about it until I was talking with a friend who runs the LBS and he gave me a response like I was insane for trusting it since it has been repaired. I explained my logic, but he even thought that it would be irresponsible since if it came loose in a group during a race bad things could happen.

I am now to the point where I am thinking that it would be best to just purchase another one and trash this one, as the elimination of the doubt that I now have would far out weigh the cost. I am still just one of those who hates wasting things, and I keep going back to the fact that they glue them at the factory. Anyone think they can convince me that it will be ok and I should just keep it until I have an issue with it??

 

[alfeng]

FWIW. If you used something like JB WELD to bond the head of the seatpost with the post then I think the seatpost should be good-to-go.

 

[bgoetz]

No I used an epoxy. I tried to twist it pretty hard and it does not move.....

 

[dhk2]

If the bond fails, my assumption is that the seat would simply twist side-to-side, but stay on top of the post. If that's true, I'd go ahead and use the seat, at least on the trainer where you don't have to worry about it failing miles from home. Since the bond has already passed your test (trying to twist the saddle), my guess is you'll be fine. Not something I'd really want to take on a big ride though.....might be good to have the new post handy to swap out for your big events.

Actually, I like the finely-machined Thomson alloy posts because of their one-piece design. CF does many things well, but it doesn't seem like the best material for a seatpost to me.

 

[alfeng]

You should be good-to-go with the epoxy you used ...

• JB WELD would just have been a moderately stronger bond because it is less likely to degrade over time the way an epoxy which cures to a "clear" amber color can ...

Presuming you "buttered" both surfaces OR used some other process ([COLOR= #808080]e.g., inserton, twst, removal, re-insertion[/COLOR]) to ensure a maximum feasible surface area was coated, then the bond should be sound.

 

[Peter@vecchios]

Originally Posted by bgoetz .

Well I a couple of weeks ago I came off of the rollers and broke my seat post in two /img/vbsmilies/smilies/redface.gif. I decided to shop ebay and found one that I purchased, but when I received it I could tell that the end that holds the seat had been glued and was out of alignment. I put it on and sure enough with a little twist it came loose. I ended up with a partial refund from the seller (best I could do) and used an epoxy to fix it. I feel like I did a good job and used a good epoxy and my thought is with as far down the post as it goes and the fact that the only way it would come loose again is a significant twist of the seat and then a pull upwards not much could happen safety wise. It is a carbon/aluminum post.

I felt pretty good about it until I was talking with a friend who runs the LBS and he gave me a response like I was insane for trusting it since it has been repaired. I explained my logic, but he even thought that it would be irresponsible since if it came loose in a group during a race bad things could happen.

I am now to the point where I am thinking that it would be best to just purchase another one and trash this one, as the elimination of the doubt that I now have would far out weigh the cost. I am still just one of those who hates wasting things, and I keep going back to the fact that they glue them at the factory. Anyone think they can convince me that it will be ok and I should just keep it until I have an issue with it??

Where you touch the bike, when those things break(pedals/handlebars(stems)/seatposts) bad things happen. Get a new post.

 

[dhk2]

Originally Posted by alfeng .

You should be good-to-go with the epoxy you used ...

• JB WELD would just have been a moderately stronger bond because it is less likely to degrade over time the way an epoxy which cures to a "clear" amber color can ...

Presuming you "buttered" both surfaces OR used some other process ([COLOR= #808080]e.g., inserton, twst, removal, re-insertion[/COLOR]) to ensure a maximum feasible surface area was coated, then the bond should be sound.

alfeng, I thought JB WELD was basically a regular epoxy with high-temp resistance. Why would it be less likely to degrade over time than others, ie, the epoxy used to bond my fork dropouts into the CF fork legs? Perhaps the black color of the resin would make it more resistant to the effects of UV vs a clear resin?

 

[swampy1970]

JB Weld tends to deal with vibration a little better than other over the counter epoxies.

 

[alfeng]

Originally Posted by dhk2 .



Quote: Originally Posted by alfeng .

You should be good-to-go with the epoxy you used ...

• JB WELD would just have been a moderately stronger bond because it is less likely to degrade over time the way an epoxy which cures to a "clear" amber color can ...

Presuming you "buttered" both surfaces OR used some other process ([COLOR= #808080]e.g., inserton, twst, removal, re-insertion[/COLOR]) to ensure a maximum feasible surface area was coated, then the bond should be sound.

alfeng, I thought JB WELD was basically a regular epoxy with high-temp resistance. Why would it be less likely to degrade over time than others, ie, the epoxy used to bond my fork dropouts into the CF fork legs? Perhaps the black color of the resin would make it more resistant to the effects of UV vs a clear resin?


Greater vibration tolerance? Probably ...

High temp resistance? Who can remember?!? I'll have to read the package!

FWIW. This is an over simplification, but in addition to the "grey" pigment, JB WELD is embedded with small fibers ...

SO, WHAT?!?

• the pigment AND the added fibers act the same way that sand when combined with cement ([COLOR= #808080]and lime[/COLOR]) creates mortar ... add gravel ([COLOR= #808080]and lime[/COLOR]), and you have concrete ...

As you certainly know, with molded Carbon Fiber, the resin is the weak link ... similarly, naked epoxy resin has limited strength ...

et cetera?!?

So, as far as joining the head of the seatpost with its shaft, if if wasn't a press fit, then it was undoubtedly bonded with some type of epoxy.

 

[vspa]

Originally Posted by Peter@vecchios .



Where you touch the bike, when those things break(pedals/handlebars(stems)/seatposts) bad things happen. Get a new post.

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