Curvature in downtube - repairable?
I have acquired an 80's Trek 620 with a Reynolds 531 main triangle. I've had it sandblasted, after which point I noticed the down tube is slightly out of alignment.
I have noticed the following:
- The TT is true and appears to be damage-free
- The fork is not bent and shows no evidence of a front-end collision
- The DT is curved down a little just below the bottom head lug
- The side-to-side/lateral alignment of the DT is decent- it's as if there was a light impact upwards to the underside of the tube, near the DT shifter mount area.
Can anyone out there tell me if I can straighten this thing? How could that be accomplished? Wood blocks and tapping, or aligning the frame via the head tube?
Any ideas or suggestions would be appreciated, thanks!
Couple of pics are on my Flickr album:
Last edited by xnetter; 12-27-13 at 08:52 AM.
The link is hosed (two http://s and truncated).
It looks fixable using a tubing block around the DT just aft of the bend in a vise and judiciously setting it straight by manipulating the frame itself.
Last edited by Scooper; 12-27-13 at 08:46 AM.
Thanks Stan- that's a good place to start.
I've fixed the link.
XN - Looks like it has a crack in the tube also. Either way, the degree of bend in the tube is significant. Guessing someone went down at speed and put their knee into it hard. Likely the fork was also bent -- I always ask "where's the fork" as typically folks trying to sell a wrecked frame will get rid of the trashed fork to hide the more obvious evidence.
Originally Posted by xnetter
Kinda of up to you to decide if the cost of replacing the down tube (framebuilder fees and materials = about $350 or so) and repainting (about $100) exceeds the final value of the the repaired frame or not. Generally I would posit that you are going to loose money on it.
BTW: In general terms, best to keep the sandblaster away from thin walled bike frames. Ok for a thick walled Schwinn or the like, but for a Reynolds, Columbus, Ishawata, Vitus, etc., based frame you should use walnut shell or soda blasting to avoid damaging the thin walled sections.
BTW: In general terms, recommend checking for frame damage before buying the next frame or bike. Laying a straight edge on the tubes is a good basic technic so you did good on this one...just do it before putting your money down. Lots of frames and bikes for sale, so pick well. And always look for a frame and fork installed with a good headset. That makes it much easier to check the alignment (using the string method)
Hope that helps
thanks for the ideas, lots of good info there. I agree about inspecting frames before purchase- in this case, the trek came from eBay for very little.
It came with the fork, I just didn't include it in the photos. It's in good shape, with no evidence of a crash. I assume it is the original (it is the correct one and the matching colour way). The frame and fork came with the correct Campy NR headset installed in good working order with no evidence of head tube or steer tube issues.
i hadn't noticed the crack- will have to look closer on that. I have checked, and the frame's in line alignment is pretty good, the damage seems to be Contained to the DT. Would you say it's not possible to straighten the tube?
Andrew R Stewart
Straightening one tube usually leads to issues with other tubes. Andy.
Andy, generally I'm in agreement. In this case, though, straightening the minor bend in the down tube should actually relieve stresses that have resulted from the accidental bend. Are there other issues I'm not aware of?
Originally Posted by Andrew R Stewart
Tube replacement would be a better cure.
No doubt. It would be a lot more expensive, too. If there's really a crack in the DT as it appears there is, then replacing the tube is probably the only option.
Originally Posted by fietsbob
Last edited by Scooper; 12-28-13 at 02:57 PM.
that tube is pretty straight, I don't think it will be easy to get it much straighter. I have no idea what's going on at the "crack," but finding out is a good idea
How does one inspect an already repaired tube, to see the extent of the issue, pre-repair? I does look like some spots were filled, while others appear to be just from sanding
The best way to inspect it is with an ultrasonic thickness gauge. The trick is finding one with with ±0.01mm resolution and a thickness range with a low end of ~0.1mm for measuring thin walled tubing with a transducer on just one side of the material.
The Olympus 38DL Plus is an example.
Some test and measurement equipment rental places will rent them short term.
Andrew R Stewart
Knowing the wall thickness is only a portion of the whole picture. As I read this thread i find it hard to really assume on what's going on, what caused the problems and the possible solutions. Sure, scenarios go through my head but to speculate out loud puts emphasis on what we, without having the frame at hand, are merely guessing at. Going back to the original post I read that the DT is damaged/bent but the TT is not. For this to be completely true the DT would have had to stretch or have been bent before the build (or the HT would have some distortion, but no ability to know this given the info we have). Just because a ruler is placed against a portion of the TT doesn't mean that there's no secondary issues there. But as I just said this is all speculative guessing. Andy.
I bet rental on that thing is more than the value of the frame. That might be useful at work though
Originally Posted by Scooper
Yeah, localized issue of the DT, while everything else seemed pretty normal was the basis of my confusion and subsequent reaching out to the group about this frame (and it's definitely awkward trying to explain what I'm seeing through text and photos, instead of a first hand inspection).
I had the frame and fork blasted by a master painter here in Toronto, and he didn't mention that anything seemed fishy, aside from the bowed DT. I feel that a lot of the marks you see in the photos are from sanding and maybe filling. They are mostly found where things attach to the tubing - ie, the FD clamp, and on the DT in question, the DT shifter clamp band. But hey, I'm no expert, that's for sure.
Originally Posted by Andrew R Stewart
You're probably right about the rental rate.
Originally Posted by unterhausen
One great thing about these portable battery operated ultrasonic gauges is that they can "see" coating thickness (paint, chrome plating, powder coating, etc.) and corrosion damage thickness. If what appears to be a crack really is, the gauge can give you a good idea of the extent of the localized damage.
There have been several times in the past when I wished I'd had access to one.
you can detect a crack with a much cheaper device, you just need a wedge