#61
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#62
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How far in does the post slip in before it meets some resistance? You need to get your calipers on the ID of the seat tube.
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Cheers...Daryl Life is too important to be taken seriously |
#63
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Cool - so it sounds like the seat post is the right size and that the fit to the seat tube is certainly in the ballpark. I don't suspect the length of the slot being the issue as Serotta built many thousands of those bikes and slipping posts are not in any way common.
So in my mind it boils down to two possibilities - - I would check that the M6 bolt has clean threads and that it's straight. Remove the bolt and wipe it clean to be sure that the threads look good and the same from right under the head to the end. If it is any way suspect put a new one in. Also give it a spin to be sure that it's straight. Many of the original quality bolts were lost and replaced with bolts that have the hardness of butter and these bolts will bend when fully tightened. If it's bent it will not clamp as it should. After typing all of this I think the best plan would be to go to your local Ace Hardware and spend 75 cents on a new M6 stainless bolt. It can't hurt. Grease the threads and the underside of the head well and try it. - the other possibility is is that you are simply not tightening it enough. We never spec'd a torque value back in the day and I have no idea just how to tell you just how tight it should be. That said i would try it a bit tighter and see what you get. dave |
#64
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If the post has grease at this point pull it out, throw some sand on the greased post and reinsert. Bet a dollar to a donut it won't slip.
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#65
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If you pull the bolt all the way out, do the bolt's threads run the full length of the bolt or do they stop short of the bolt head? Is the bolt itself, and under the head greased?
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#66
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The file you would want to use is an American Pattern 4" round file with either a bastard or 2nd cut. They probably don't have it at your local hardware store. A 6" round file is pretty commonly available and you can use just the tip of it to extend the slot. Of course you can take it to your local frame builder too if this kind of work makes you nervous. |
#67
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Been there
My CSi had the same issue. Gradual slip over a 100 mile ride. I tried three different posts, all measured between 27.14 and 27.16 at the relevant points (using Helios dial calipers - I put myself through college and grad school as a machinist). I tried paste, grit and even rock climber's chalk. Some helped, but none solved the issue. This solved the problem once and for all.
http://landlordscycling.com/2012/01/...uill-seatpost/ Between the clamp and the quill, both tightened to spec, it's been rock solid for years. |
#68
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Interesting thing I found while on the forum, reading another thread.
Doug Fattic and Dave Kirk have already suggested the length of the seat tube slot can be too short, inhibiting clamping force. Well, Tom Ritchey mentions in a display of the Road Logic frame that the seat tube slot is longer, to deal with carbon seatposts. Can anyone measure the slot on their recent vintage Road Logic and tell us what the length is?
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http://hubbardpark.blogspot.com/ |
#69
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#70
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A time machine. You'll have to find a used one.
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#71
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A 1 1/8" slot minimum is an observation from another frame. But the OP bike has a fastback seat cluster, which locates the bolt lower from the top than a more classic cluster:
So 1 1/8" might not be sufficient given that the bolt is 1/4" lower on the OP bike. I'd lower the slot. |
#72
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With the benefit of hindsight, I'd say try the paste first. If that doesn't work, add the shim (and you'll be surprised by how narrow the shim will be, but using snips on a soda can is easy-peasy-lemon-squeasy). If that doesn't work, do Old Spud's knurling thing. If that doesn't work, get a different bike. |
#73
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#74
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I think 27.4's didn't come in for at least another 10 years, maybe more, but I'm not certain. I do know that any Paramount I have seen and could check from the late 60s to mid 70s had a 27.2 post. |
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