FBinNY 

Despite the name, JB Weld has nothing to do with welding. It's a reinforced (and colored) epoxy resin. It doesn't have nearly the strength of aluminum, so unless reinforced with fiberglass or the like, or built up damm thick it won't natch the strength of the tube that failed once already.

Also it's elastic properties may not match that of the post within well which will cause the job to fail sooner rather than later.

3alarmer 

.
.
....................I threads like this one.

Airburst

Oh no, not bloody JB Weld again!

LarDasse74

You are ignorant.

ollin

Interesting developments! (I always wanted to write that) : I did some measurments and it turns out that the post was inside the frame a full 16cm; this means it went further under the weld of the top tube miter (and it's a large, oval shaped miter, this one) for 6 more centimeters! Not only that, but i noticed that the seat tube starts growing in diameter at about 10 cm from the top!!!(just after clearing the top tube weld) Meaning that however long your seat post may be, it will not matter because it wont be even touching the walls of the seat tube after just 10cm!!! How can this be rated at 300lbs?!

pierce

hey, JB Weld got my son home from the middle-of-nowhere Death Valley, when he busted a walnut sized hole in the oil pan of his volvo... they used some tin from a soda can, and just about a whole tube of JB, and it held well enough to get them home. he only had 2 quarts of oil on him, but a passerby (in a jeep 4x4) gave him 2 more quarts so it was on the dipstick even if not optimal.

I *told* that kid not to take that low-to-the-ground 850 turbowagon offroad, hah hah.


but yeah, its not going to work that well on this, at least not without being really ugly. maybe if you had a tube that was a snug fit over the seatpost, you could epoxy it in place, but even then, I'd use a different epoxy than JB.

ollin

Sorry forgot about imperial funnyness: 16cm = 6.29in, 6cm = 2.36in, 10 cm = 3.93in. According to Lord Google of course.

ollin

Hmmm, maybe the developments were not so interesting after all. It just seems like a terrible design flaw for me!

FBinNY 

Design flaw may be too strong. There's no perfect design for seat clusters. The traditional way of using pinch bolt ears hat are part of the lug or frame (as on a typical steel frame) has the drawback that if the ears fail as they sometimes do, the frame is toast. Also this doesn't work well on welded aluminum frames, so the alternative of an extended seat tube with a collar is pretty much SOP for aluminum frames.

It isn't perfect because it's vulnerable to seat post flex under heavy loads.

One would think that the post would buttress the outer tube (two tubes are better than one) but this isn't always the case. Differences in flex characteristics can cause a stress riser at the weld leading to your problem. However this isn't a problem in 99.9% or more of frames of this type.

So there's no perfect solution and it's a matter of balancing the benefits and drawbacks of either design. Given your weight, I'd shift the balance in favor of zero extension above the top tube, and/or reinforce the post in the area where it enters the frame.

Stated wheight limits can only be taken as coarse guidelines, because there are significant variables, such as [pavement quality, tire/wheel selection, and riding style. I agree that this isn't good news for heavy riders, but you have to understand that designers design for their intended audience. If bikes had to be built for heavy riders then they would be overbuilt for the vast majority of riders.

I understand that heavy riders are handicapped it their choice of bicycles, but those are the breaks of the game.

LarDasse74

Most of us big guys understand this and are prepared to have things replaced, or buy something a little heavier to begin with. The flip side of this is that we are often all too willing to accept our weight as an explanation for a problem than really shouldn't have happened at all - like when the spokes start breaking on a 3 month old machine built wheel, an ignorant but well meaning shop worker might say 'well, this wheel must not be meant for heavy riders,' when in fact a big rider may hasten such a failure, but not really be the cause.

fietsbob

Looking at the way you used the bike, Ollin. hauling stuff, I suggest a nice steel frame ,
the Surly LHT is Popular here.

[maybe there are still Mexican made Windsors in the used market]


IDK what is Local to Guadalajara, México, But There is Freight Shipping all over the world.

Chombi

Not sure how well they work with aluminum frames, but what about a quill wedge type seatpost that works like a quill stem. Only other problem might be the required legnth of the post as I have never seen a quill wedge post that long, but maybe one can figure out something with a long threaded rod and a nut welded on one end..... a bit of "McGuyvering" will definitely be needed to make it work.....
Chombi

Airburst

It would still need to wedge against the top of the frame, meaning it wouldn't remove the forces on the crack.

FBinNY 

If it's properly secured below the top tube, it might still flex above and extend the crack. But it wouldn't matter, since the only purpose of the extension is to attach the clamp, which is now no longer needed. So if you break off an non-functional seat tube extension, does it matter?

If you're concerned about the crack you can use a hacksaw to cut it off cleanly, and clean it up with a file. (assuming you have a way to secure the post)

fietsbob

Bodge ahead warning :

Going back to a plain seatpost offers a Potential .. as they all are reduced to 22.2mm/7/8" at the squared off top.

You can make a wedge out of the lower portion of the post sawing it off at an angle*, then cramming a Star Fangled Nut
in from the angled top you can pull it Up and the star nut will grip, as you tighten a bolt (6mm) that is Long enough
to reach the top of the post ,then you have a Flat washer under the Bolt head.

*A Power Band saw will make a clean Cut .. Hacksaws blades then to wander because the Operator is only Human..