FBinNY 

I guess it wouldn't be fair take his cash on my old Frejus 10s, which I semi retired 75,000 miles.

Davet

TREK made an aluminum equivalent to the 520, it was called the 540. I bought a new 540 in ‘98.

Duragrouch

That area of the downtube is highly stressed, not only from vertical fork loading under rider/bike/cargo weight, aft fork loading under braking/pothole/frontal impact, but also torsional loading from pedaling forces, countered by handlebar forces, and all of the above being greater under touring loads, and the 520 is designed specifically for loaded touring. However, vertical loading (the greater occurance) would load the downtube in compression on top and tension on the bottom, and fatigue cracks happen mostly in tension, thus, the crack being on top may indicate a high occurance or severity of aft loading from braking, potholes, frontal impact, and the combination of all of those.

Welded structures can be very sound, even with heat-affected zones, for both steel, aluminum, and other metals. This can be accomplished several ways:

- After welding, post-heat-treating the entire structure. Example - Early Cannondale frames welded of 6061-T6 aluminum, then post-heat-treated. Note: 7005 aluminum was developed specifically for bike frames to avoid the need for post-heat-treat after welding, saving both cost, and improving dimensional stability.

- Some alloys are not degraded by weld heat, because they have a high "hardenability", i.e., the alloy does not require fast liquid quenching following elevated temperatures to achieve hardness and strength, but just cooling in air does it. Steels high in chrome and moly, and most especially stainless steel with very high chrome, is notorious for this, you're drilling without coolant, see just a spark of red, it hardens instantly, and it's like trying to drill through glass. This is why the vast majority of kitchen knives are made from "German steel", X50Cr15MoV or DIN 1.4116, it has so much chrome, it hardens very easily without fast quenching which can warp blades. (A noted metallurgist online theorized it has too much chrome, which hooks up easily with carbon to form chromium-carbides, which are not that hard and have a large grain size which causes numerous issues; He reduced the chrome to bare minimum to "saturate" the iron for corrosion resistance but not a touch more, so the carbon hooks up instead with the vanadium, very hard carbides (so hard you cannot use a typical aluminum oxide sharpening stone), and very fine grain structure. But this also required much more expensive processing to make the steel, thus an order of magnitude more expensive, and very precise heat-treating down to the degree and second, increasing costs there too. But the steel is 10 points higher Rockwell-C, and 6X the toughness, very hard to get both qualities at once.)

- Good weld shape: If convex, i.e., weld bulges outward, that creates a stress concentration at the weld boundary with the tube, commonly cracking there. Concave, either good weld (as seen in the frame above, great weld, no failure there), and with post-weld "dressing" (filing or sanding), even better. The Cannondale 6061-T6 frame I had, the welds were big, like fillet brazing, and then dressed with power strip-sanders to a lovely concave radius and fine taper to the tubes, with no undercut into the tubes, and this gives fabulous stress distribution across the weld and tube interface. That's why I was excited to see a new video of a Dahon Archer (2X gearing, discs) that also appeared to have smooth dressed welds, that would be a step up for durability and not just aesthetics.

biker128pedal

For kick if you have the receipt take it in to a Trek dealer for the lifetime warranty claim. Need the receipt. . Just to see if Trek wants to inspect it. Because it’s been repainted I doubt they will do anything. But who knows they may have a 520 rim brake frame they want to get rid of and score some PR points.

Anyway I had a Raleigh aluminum man frame crack close to the head tube but on the underside. I caught it early and Raleigh honoured the warranty and replaced the frame. Also they included all the parts which did not transfer from the old frame. Like the seat post was a larger diameter.

Like you I got my moneys worth out of the frame.

grumpus

What you need there is a can of high build primer. I'd be interested to see what it looks like inside the head tube.

cpach

For what it's worth, it's actually pretty possible that Trek would warranty that as a lifetime frame replacement if you can provide proof of purchase, as someone who's worked at a Trek shop. Would probably send you a current generation 520 frame, which admittedly would at the very minimum require disc brakes and compatible wheels to transfer over.

Duragrouch

If the OP registered it with Trek upon purchase, they may have record of it. IIRC, I registered my '89 Cannondale when purchased, back then it was by snail-mail.

biker128pedal

I submitted a warranty claim on a 2006 Madone I had registered with Trek. I still needed a copy of the receipt. This was in 2021.

gearbasher

To jump on the high mileage bandwagon: I bought my Maza (TSX) frameset in '96 and didn't build it up until '99. After today's ride it now has 96,979 miles on it. I should break 100K sometime in July.

BTW: I've had two frames crack in that spot, but both were involved in front end crashes. I got about 8,000 miles after the crashes before the cracks started to show.