Serotta Legend Seat tube Question

[Brian Smith]

Originally Posted by pbarry

If it's ovalized, reaming is not the best solution. A proper mandrel might make it more round--Buldogge's recommendation for using a sacrificial steel SP is right on. Find the correct clamp and a slightly undersized post, and all should be good. Use carbon paste if there's slippage...

It's hard to offer complete advice without knowing what is wrong with the frame, or indeed what size tube and posts are being discussed. I would, however, disagree in general that an undersized post and some goop is the best solution for an oval seat tube. To me this is like a post-accident automobile's bumper fallen cover affixed with duct tape as a solution, in that the underlying damage is the real issue. Something sharp is causing the scratches on the post being inserted. That something should be identified.

cm - DKG was a supplier to Serotta for clamps in the 30mm sizing, if the frame is of the age that I am imagining and used that clamp, and they are still being offered here:
DKG Sizing Page

It is likely, in my experience, that whether the tight fit and scratches are due simply to a past over-tightening of the clamp, perhaps to accommodate a 27.1mm post, then remedied by manipulating the tube above the slot and sweetening the edges of the slot, or whether they are due to the interior surface of a weld such as the seat stays, a reamer may be required to achieve a nice sliding fit.

If you were anywhere nearby, or wanted to ship it, I'd offer to have a look at it and see about fixing it. This is not an un-heard of issue.

[pbarry]

Good on you Brian for the offer. Without seeing the frame, we are all just speculating here.

[soulspinner]

Originally Posted by pbarry

good on you brian for the offer. Without seeing the frame, we are all just speculating here.

+1

[Saint Vitus]

Thanks Brian for sharing your firsthand knowledge of this issue

[cmbicycles]

Brian, thank you for the info, the dkg link on the seat clamp, and offering to look at it. The frame, I believe, is around an '03-04 custom legend, its a bigger frame with a 63cm seat tube. The 29.5 clamp dkg offers should fit pretty close based on my measurement.

As for reaming the seat tube, would a helical reamer specific to 27.2 be best or will an adjustable reamer work as well/better/worse? Is this something that is best left to a machine shop or would hand tools and lots of cutting fluid suffice? I've reamed several steel and aluminum bikes using an adjustable type hand reamer, but ti is generally harder on tooling.

I'll try to post a picture of where the tube is misshaped, so you can see what I am talking about with that issue.

[Brian Smith]

Originally Posted by cmbicycles

Brian, thank you for the info, the dkg link on the seat clamp, and offering to look at it. The frame, I believe, is around an '03-04 custom legend, its a bigger frame with a 63cm seat tube. The 29.5 clamp dkg offers should fit pretty close based on my measurement.

As for reaming the seat tube, would a helical reamer specific to 27.2 be best or will an adjustable reamer work as well/better/worse? Is this something that is best left to a machine shop or would hand tools and lots of cutting fluid suffice? I've reamed several steel and aluminum bikes using an adjustable type hand reamer, but ti is generally harder on tooling.

I'll try to post a picture of where the tube is misshaped, so you can see what I am talking about with that issue.

cm -

I would first try to remedy a collapsed slot, if present, then remove any sharp spots first along the slot and then anywhere else in the area that contacts the seat post.

Only after all of that, to remedy the snug fit, I would suggest the adjustable reamer, creeping up on the fit 1/4 turn of the adjustments at a time until satisfactory. A beautiful and proper helical reamer such as manufactured by Silva is designed for a different job. Reamers are not meant to bore, although in bicycle seat-tube land they are often used for that job. Titanium is hard on tooling that is not designed for titanium. The fact that bicycle seat tube reamers designed for titanium seat tubes don't exist is something apart from those facts. Misuse of the tool can easily be harder on it than its use in titanium. The fact that you've used such an item on various other frames lessens your risk. The cost of a cheap set of replacement blades for the adjustable reamer can be lower than that of a halfway decent contemporary 27.2 seat post. Even if by some twist of fate the blades were 100% ruined by this single use, it is money reasonably well spent. A static helical 27.2 reamer may well not complete the job. It's not imperative to go crazy with lubricant amounts in a careful hand reaming, but they will reduce gouging if your reamer is pretty fresh.

Perhaps the photos will be useful to identify additional recommendations or otherwise provide clarity in identifying the underlying issue, but it does sound like you're trending in the right directions to resolve the seat tube issues. PM me if I can be of any assistance.

[pbarry]

Brian, cmbicycles has calipers, yet you still recommend reaming, as in your first post in this thread, and now ask for images but have never asked for measurement of tube ovalization or deformation..

Let's go back in time: There was a distinct decision made at Merlin, (years before Serotta jumped into the Ti game), to make a machined seat-top that would hold up to welding deformation and provide the customer with reliable and smooth seat post adjustability. These inserts were machined in-house and were the most expensive manufacturing process in Somerville.

The process: Start out with schedule 40 stock; machine the relief on the top of the ST insert; machine the taper, (later butt welded); Cut off piece. Pieces were then press fit into the run of seat tubes, then had binders and BB's welded in fixtures, then slots and relief holes cut. After the frames were welded, there was still light reaming to be done in finishing..

IMO, the ST collar/reaming-tubing after welding route is a shortcut adopted from the mtb world, and I was surprised when Serotta went this way for Ti.