miamijim

I looked over a 3Rensho frameset at the request of a local rider. The seat tube experienced a clean break about 1/2" above the BB lug.

Somewhere along the way the break was brazed together. From what I was able to see it didnt look like the edges were proximated correctly. I told him it was toast and needed a new seat tube. As you could imagine the owner was disappointed to hear my opinion.

We briefly discussed sleeving but there's no way to get an internal sleeve down that far and I doubt he'd want to externally sleeve it. His other concern was the ability to find the same kind of tubing, I told him he's probably be stuck with something other than what it originaly had.

Any thoughts or comments? Any rough estimates on cost without paint?

NoReg

Tube wise, it is mostly under compression, in column, so the more rechercher aspects of any one tube over another are not going to be evident. as long as the profile is similar, say single butted tube, then the weight would be the same also.

The only stupid idea I would have other than what you have suggested is that it might be possible to make a part that was a really special looking badge that was consistant with some other aspect of the design. Like a nice little band holding the deraileur bo - if it was higher, and a road frame.

miamijim

These are best pics I could do with my cell phone. It was well into dusk so the lighting wasn't optimum...

unterhausen

toast. A new seat tube is in order, it doesn't really matter what kind of tubing, he's not going to be able to tell the difference.

Seat tubes are under cyclic loading, and I'm pretty sure they into tension fairly often. That's worst case for fatigue life, and probably why seat tubes break so often. Although seat tube failure is rare on lugged bikes.

I always look at Bilenky before I quote a repair, they seem pretty reasonable. In this case they want $275, which seems high to me. Since I've never done one, maybe I haven't seen the problems that they have. I can understand that charge if it was welded or fillet, but for lugged it seems like the repair would be easier.

legalize_it

how many hours start to finish do you think it would take? at $60/hr, thats about 4.5hrs labor. seems very fair, if not a little low!

miamijim

4.5 hours to replace a seat tube? Why so long? Over in C&V there was a guy who had a TT replaced for $150

unterhausen

that's the thing, they only charge $200 for a top tube or down tube. Which seem to me to be a little harder to do.


The only thing I can see is that you can't blindly sweat apart the seat cluster, reaming might take a while.

legalize_it

unter-
if bilenky is charging more for a seat tube repair, then it must be harder or more time consuming than a TT or DT (for them). they do a lot of repairs.

miamijim-
i was making generalizations and throwing around hypothetical numbers to try and make a point about repairs and billable time.

NoReg

Under tension, it should last for ever? A lot of meat in a tube, compared to say the wire on the forestay of my boat, and the loads are minor. But I'm no engineer, just astounded.

Actually it's only about 30% more cross sectional area, now that I do the math, but the loads on the forstay from a multipart tackle and all those wind loads, and the bouncing around constantly at anchor. Anyway, not much of a comparison really, apples and oranges.

unterhausen

tension-compression is worst case, tension-tension is also bad. A structural member that is always in compression is not going to suffer from fatigue crack growth like we see in bicycle frames.

tuz

Didn't Kurt/Cudak have a ST replaced recently? I think M. Terraferma in FL did it. They cut the ST and reamed/grinded the sockets, then silver-brazed a new ST. You could ask how much it was.

If you remove the tubes with heat I can see why the ST is harder then a DT or TT. Here is Dave Moulton's take on it.

unterhausen

Nice link to Dave Moulton. I need to find some firebrick.

miamijim, do you have pictures of the seat cluster?

miamijim

I felt inside the seat cluster area and there's no evidence of a seam so I'm not sure where exactly the seat tube itself ends.

zzyzx_xyzzy

It goes all the way through the lug.

Seat tubes are in compression when you sit on the saddle and in tension when you stand on the pedals.

miamijim

Over the years I've seen a few that dont but was fairly certain it did on the 3Rensho. The pics dont show it too well but in person the seat lug/ST thickness isnt very thick!!!

unterhausen

very, very few lugs have a shelf for the top of the seat tube to rest against. The only good reason for it in my view is on stainless lugs where you would want to polish the top surface of the lug around the top of the seat tube. Most frame jigs now use a cone to hold the seat tube at the top so it's best to have a round tube up there to register against instead of the pointed seat lug.

Seat tubes are really thin at the top, that's why I advise people not to try to use a hacksaw to get a stuck seatpost out on a good frame.

Is the tubing sticker still on the frame? Do you know what it was made of? There might still be some Tange Prestige floating around if that is what it was made of.

miamijim

There is but the work computer isnt playing nice..... Its the 'elephant' tubing decal.

t4mv

3Renshos are usually Ishiwata. 022 or 019 depending on size, I think.

Look on the "elephant" decal and it should say Ishiwata.

ultraman6970

Im not a builder but i have seen how to fix that, actually i have seen 3 ways to do it.

1 use an internal sleeve and braze it. The problem i see in the picture is that probably you will end up with crystallization so better go with #2 (just in case, wonder if the BB shell is already in bad shape for overheating)

2 cut the seat tube in the middle and take a piece off of it, heat the BB take the tubing from there. Heat the top and do the same in the seat area. Since you have a problem with the lug probably solution 3 is the best.

3 cut the seat tube in the middle as before, heat the bb as before to remove the seat tube at the bb area, heat the upper part and get the seat stays off the lug, then heat the lug again and take it off the top tube and replace the seat lug with a new one. Since you have to cut the seat tube anyways and keep the same shape probably you are better doing this than trying to save the seat lug, the guy wont even notice anyways once all is painted and brazed all together.

Have seen repair like this done in one hour. But we are taking a builder that is right now around 70 y/o so the guy have been doing stuff since he was maybe 10 and with no jig, but they have an Italian table that is maybe 70 years old, family bike builders tradition. I regret so much have been in his shop whole days looking and actually have not learn a single sh@@ttttt, when u are a kid u dont see these things.