bobotech

I am looking for a 700c aluminum frame with canti posts and found a really nice BMC frame in my size. Issue is that it has two cracks by the top of the seat post area. It appears that someone overtightened the seat tube and crack appeared .

I could get the frame for like 50 dollars. How much more to have it repaired? I wish I had pics but I don't! I mean if I could get it repaired for 100 or so and then have it powder coated for 50, I think that would be fine for a high end repaired frame.

Specifically looking for cyclocross frame for 700c with canti posts and those are impossibe to find anymore. Heck I'd even settle for a good brand hybrid flatbar frame but can't find anything like that anymore.

dsaul

If it is aluminum and it has a crack, its most likely trash. The most common alloys used for bicycle frames need to be heat treated after welding.

With that said, I welded a seat tube/top tube crack on a friends 6061 aluminum MTB frame last year and he says it hasn't broken yet.

AnkleWork

Maybe just ride it and monitor the cracks. Mark the ends or stop-drill them.

First make sure the seatpost and clamp are the correct sizes.

HerrKaLeun

I'm curious how you would define a not so nice frame? Cut into pieces?

sounds like you are looking to buy that.. don't.

Jicafold

Around here the rate for aluminum repair for that is $50.

bobotech

I was researching the BMC brand, it appears that they are higher end bike brand. So I would surmise that the frames that they sell are probably considered pretty decent.

Are they not a good brand?

HerrKaLeun

A BMC frame in mint condition likely is good. But the one you consider buying has cracks, which I would consider not good.

When buying new, you can go by what their typical quality is. But used is individual and this one has cracks. And who knows what other hidden damage. Like a Honda Accord typically is a good car, but one that is totalled isn't.

AnkleWork

Perfect good/bad - black/white thinking example for this forum. "It depends" is way too subtle here.

Canker

Well if that cracks completely it won't kill you so if you really want it and it is only $50 go for it. Personally I'd skip even bothering to try fixing it. Go to a autoparts store and buy a hose clamp to put it around the crack on the seat tube and call it good.

HerrKaLeun

If it were dents or other cosmetic issues, yes it would justify a more subtle judgment.

Cracked frame is black/white. Cracked frame is junk. Especially if OP hasn't bought it yet. Are we really discussing if buying a frame with known cracks is worth buying?

AnkleWork

Another good example.

Are the supposed cracks reasonably repairable? Are they more than cosmetic? Do they even exist? Black/white thinking doesn't need answers to those questions.

squirtdad

a picture would certainly help evaluation

Personally I don't ride frames with cracks......even steel and especially wouldn't with aluminum. I don't like the odds.....maybe if fails, maybe it does not. If it does fail, aluminum fails pretty quickly, so if you are at speed to may be an ugly crash. I have good health insurance, buy would really prefer not to use it. And depending on the aluminum type, a repair may add more overall weakness.

Wilfred Laurier

Avoid.

Any repair would further weaken the frame and it will likely fail again, but this time it will be your problem. Keep looking and another frame will be available soon that does not have cracks in it.

'02 nrs

many crack in that are due to over extended seatposts,metal fatigue.if the seller is the org. owner ask them if they tried a warranty claim.or if you do go with it try asking BMC for a crash replacement discount.

ljsense

Do the cracks reach to the top tube or into the welds?

If they start at the top of the seat tube and stay above where the seat tube joins the rest of the frame, just drill holes where they end, make sure you have the right diameter seat post, and sufficient seat post length so that its bottom extends well below the junction with the top tube. Aluminum is easy to drill. Any decently sharp bit that's around 1/8" will do the trick. Just make sure you hit the end of the crack with the hole you make.

In effect, bike frames already have a "crack" at the top of the seatpost with a stop crack hole so that the seat post collar can flex the frame and close it around the seat post.

If the cracks go into the weld, or below where the top of the top tube joins the seat tube, or there are more than two of them, you can probably find a better frame for what you're preparing to spend on this one.

A crack at the top of the seatpost isn't particularly dangerous. The racing bike I got when I was 16 eventually broke at the seat lug. It made a sound, and got real flexy. I had the seatpost up too high -- it wasn't inserted far enough into the frame and eventually the leverage cracked the seat tube clean in two, right at the lug below the seat tube. I rode home no problem.

Someone probably rode this bike with minimal seat post insertion, or put a seat post in that was too narrow and just kept going on the bolt, through the shattering sounds, wondering why it wasn't getting tight.

wsteve464

Does the seat tube extend above the top tube by a good amount? If so cut the seat clamp off and buy a seat post collar for $20 or less

https://www.amazon.com/Best-Sellers-...-goods/3494301

If needed you can get one that has 2 different size clamps one to the seat tube and another for the seat post