[CR]Was: Masi progress; now, mis-shaped seat post hole....


From: BobHoveyGa@aol.com
Date: Mon, 10 May 2004 02:30:12 EDT
Subject: [CR]Was: Masi progress; now, mis-shaped seat post hole....
To: classicrendezvous@bikelist.org


Thanks to everyone who wrote, on-list and off, concerning my seatpost problem (a distorted seamed steel post with a dip in it had caused the ears to collapse into the dip, resulting in severely toed-in ears and a hole way too small (front-to-back) to insert the correct-sized post).

Dale's advice seemed the safest (see below for those who missed it), unfortunately I ended up working on the bike before I read his post on Sunday morning (I'm usually not up that early, but Sieren woke us all up at the crack of dawn so she could give Mom her mother's day present).

I decided to go with the drift punch in the bolt hole method, and here's why: The distortion was almost entirely in the ears... front to back diameter was way too small, while side to side diameter was just a hair (<.1mm) oversize (which I guess is probably normal when there's no bolt installed). If I had levered the slot apart, the expansion might have affected the entire tube, but mostly I think it would have been the side-to-side diameter... it would have gotten even larger and the front-to-back axis might not have grown much at all. But by levering with the drift punch in the binderbolt hole, the fulcrum was on the outboard side of the ear, right where it met the seat tube. Only the 1cm or so distance from there to the slot would be appreciably affected by the bending force... So when I applied pressure (very gently, about three or four successive tries on each side, alternated with test-fitting a proper-sized seatpost) the inboard side of the seat tube and ear bent outwards, the outboard side pretty much stayed put and according to my dial caliper the overall side-to-side diameter didn't budge. The result? Now the 27.2 post slides in and out with firm but gentle pressure and when it comes out there's not a scratch on it, just a little grease. And the outside faces of the ears are parallel again. The bolt goes in straight, and when tightened the seatpost stays put. So I guess I lucked out. Whew.

BTW, I wouldn't recommend this method to anyone who doesn't have a tapered drift punch or rod that fits the hole very snugly... I just happened to have a nice selection of about 20 to choose from thanks to a retired machinist's yard sale. If the fit is not very snug, I would think there'd be a good chance of scarring the bolt hole or chipping the paint.

Bob Hovey Columbus, GA

Dale wrote:

I would get your LBS to order a cheapo aluminum or steel 27.2 seatpost (or whatever the correct size is..?), the ones that have a taper toward the top to accommodate the "old fashioned" (non integrated) seat clamp. Then securely hold the frame in a big vise using soft jaws and clamping the bb faces (remove BB first). Then turn the straight seat post upside down, heavily greasing it, insert the small end into frame, and push/tap/persuade into frame in a twisting motion. This should spread and make more round the seat post "hole" in the frame. Do it progressively and try not to rock the post to and fro, as this can also ovalized the hole... Then have your LBS use his precision ream to accomplish the final machining of the frame to a perfect 27.2 I.D.