Freefallman

I just bought an aluminum frame bike off craigslist and I threw it up in the repair stand to clean it up and noticed a small crack below the seat stay up near the seatpost. This is clearly a case of overtightening. Did I buy a lemon? Is it junk?

spdntrxi

yes ...return it (if you can)... should be able too.

fietsbob

Or they put the seatpost up too high, lacked enough in the frame .

Andrew R Stewart 

Yes the frame is damaged and likely beyond any cost effective repair. Also luck is that if a frame were to break that is a good spot for it to do so. As long as the post is further down in the seat tube it will help stabilize the frame's integrity while you coast to a stop. (Not so for other breakage points...) The crack is running along the edge of a weld. this is a common starting point for cracks to develop. The stresses are focused there and the strength changes from welding collectively make this location susceptible. Adding the clamping/bending aspects just signs the deal.

No it is not a sign of over tightening unless a too small post was used. Andy.

FBinNY 

I suspect it's the result of being ridden with a too short post, or with a thin wall post and heavy rider.

If you have recourse to get out from under, do so, unless the bike was dirt cheap (components worth more than the bike).

Otherwise, there's nothing you can do to resolve the issue except weather protect it. Use a strong post long enough to extend 1-1/2" below the crack, so the post is buttressing the tube. The rigidity of the post is key here because if the post flexes it'll work the tube at the crack until it's toast. So consider this a case where a cheap, overbuilt post of low alloy is better for the job than a good one.

Freefallman

Thanks everyone. I contacted the seller and it's bit unclear as to whether he's going to refund me. I contacted him within 1.5 hours of purchase but it's caveat emptor often on craigslist. Hopefully the guy has integrity.

The bike has a super long seatpost in it now so it's possible they were aware of the crack. So what I'm getting here on this thread is that a failure at this point wouldn't likely be fatal but something to be avoided nonetheless?

dsbrantjr

If you are stuck with the frame, besides the previous suggestions you might consider "stop-drilling" a small, clean hole at the end of the crack if you can get to it. This will tend to stop the crack from propagating farther and is a common fix on small cracks in aluminum aircraft parts.

FBinNY 

As long as you have a post inserted well past the crack there's ZERO chance of a failure being fatal -- to you. OTOH, it will be fatal to the frame. You might want to consider drilling "stop holes" at or just beyond both ends. I have mixed feelings on stop holes. Some people report success, but I've found them to sometimes become starting points for cracks going off in a different direction.

Either way, you're counting on the post to bridge the crack and buttress the tube across it. As I posted earlier, that wants a post which is stiffer than most light posts.

cale

There are lots of things the OP can do.

In addition to FB's good summary of condition and risks inherent with any attempt to "ride" this jalopy, You need not freak out just yet.

I believe you can stop the crack from spreading by relieving stress from below the crack. The part to do this is some sort of tube clamp. The clamp is positioned below the crack but in that area of the tube that is slotted. It should be tightened no tighter than the seat bolt above it and should not be used with out the seat bolt also torqued in. The combination of two clamps will permit lower torque values overall.

I know there are a wide variety of clamps and offer the one shown below as a modest contribution to any interest you might have in pursuing the suggestion further.

spdracr39

Can that be a factory seat post bolt? It looks jury rigged to me. I have never seen one that would also pull the seat stays together like that.

a77impala

If you are stuck with the frame get the longest seatpost that will fit and clamp it below the crack. The post will provide the support to prevent further damage. imho.

RoadGuy

Actually Trek Road Frames (lugged steel, bonded aluminum (1000-1400 Models), and some composite (2000-2300 Models) frames too) made before 1993 MY are like that (seatpost clamping bolt going through the seatstays).

As far as I can tell 1993 and newer treks all have the clamp above the seatstays. This is a quick way to determine the approximate age of a Trek road frame.

Freefallman

Is that just a seatpost collar or is it something else? Given that this is below the seat stays I wouldn't be able to use anything that just slid on...

cale

It's a braze-on derailleur hanger. So it's sized for a seat tube and hinged to get behind the seatstays. Here's a different one, same idea. Universal Cycles -- Cinelli Braze-On Front Derailleur Adapter

More stuff that clamps. You'll need to know your tube size. https://www.google.com/search?es_sm=...09.PeXgYAE5tSc

FBinNY 

I agree with Cale, that a clamp may help slow or even stop the crack from growing. But I disagree about the placement.

IMO, the place for the clamp is directly over the crack, straddling it above and below. That, combined with the post inside will splint the tube, and help carry any stress around the damaged area. Ideally the clamp should be a bit thick, but more important as wide as possible. If it weren't so damm ugly, I'd suggest a stainless steel hose clamp.

However, if I were the OP, I'd simply mark off the ends of the crack and ride and watch. If it stays as is, so much the better. Or, if it grows, then take further action.

SquidPuppet

Why does that make me nervous?

fietsbob

Its an adapter band to use Braze On Type FD's


Yup, seat post collars have an edge shoulder and are not hinged to open .


A radiator Hose clamp can also do the job.


a seat post sizing shim if long enough to go below the Crack can add material on the inside ,, then you use a smaller seat Post in the Shim

USE*, & QBP problem solvers shims , are 4" long Have one mis shipped wrong size LBS got A 'Wheels' Made one It's not as Long..

* UK USE is 25.0 ID; I Have a 27.2 and a 27.0, Re used My AlAn's seatposts in steel frames for a while

QBP has a range of OD with a 25.4 ID IE 1 inch.

rmfnla

Cracks happen...

fietsbob

Amtrak then ... dont Fly.

DynoD500_SR20-d

Funny how this is Ribble Frame. I have a 7005 frame that has this minor crack too. I am going to stress drill it. My seatpost goes way beyond the crack into the frame too

78rr

Weight, seatpost height. . .

unterhausen

I really don't think that any responsible aircraft maintenance person would stop drill this crack. People have heard of stop drilling and recommend it with no technical expertise to back it up. Stop drilling is a sheet metal repair, and there is some controversy over it actually working on sheet metal. The end of a crack has plastic deformation that tends to keep the crack from propagating.

I never worked on large passenger aircraft, so I dont' have experience with the repair of the sheet metal on that kind of plane. On the planes I have worked on, the crack would have been patched or the aircraft modified to remove the crack. I assume that's usually the case when parts are stop drilled, don't think they just fill the resulting hole with sealant.

Someone recently told me that his shop stop drills and then welds. Okay, whatever makes you happy, but welding past the end of the crack does the same thing without the hole.