Thorn Cycles Forum
Community => Thorn General => Topic started by: paulsc on October 02, 2009, 06:06:03 PM
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I hope this doesn't come across as a rant but I am really disappointed in the seat post binding bolt set up. It is ugly and the welds seem really inadequate. The bolt actually bends slightly when it is tightened and if you look at the design, it has to. I wished Thorn would have just used a separate clamp which is what I am having done to my Sherpa next week. I found a local builder who is going to remove the current binding bolt set up and I will install a clamp like a Salsa. At least if I ever have a seat post slipping problem, I will feel more confident in tightening the bolt. Now I worry the a weld is going to break or the bolt will. Perhaps the welds on my bike were done on a Friday before a long weekend. The system on the new Nomad is much better since it has a reinforcing collar and it looks great. Considering how well thought out the Sherpa is, I really think this part of the bike could have been done better.
I am sure this must be blasphemy to you Sherpa lovers, but hey, I am one too :).
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can't say mine look's bad quiet neat actually and i never had a problem with the post slipping.
ah you must have got a dud i would say you would have endless troble with that particular bike better change it quick..
only pulling your leg enjoy your sherpa it's a fantastic bike.
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My XTC seems a similar setup and I have just snapped the bolt leaving the thread in place. Took some careful work with a hacksaw on the remnants to remove because of the way it deformed at the point of the break.
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Malcom,
Thanks for confirming my thoughts but I am sorry yours broke. The switch ended up costing $25 including the seat bolt clamp. Rattle can paint job provided by yours truly. Here are the before and after pics:
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Yep, same problem here and it's a RavenTour of 2007 if that's relevant. Seat post gradually slipped and I kept adjusting till the bolt snapped from fatigue. Cycled home like a BMX-er, would have been a right royal pita on tour.
My solution was to bulk out the seatpost with a bit of drinks can - greased with coppper grease - and that means the bolt doesn't flex so much. Also fitted an overlong bolt to enable cutting a slot. In my toolkit I've addded a wee bit of junior hacksaw blade, a wee screwdriver and a spare bolt.
I like your solution, paulsc. Except it makes the seat easy to steal, no?
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I have the same problem on my Raven Tour bought in 2006. My solution is to carry a few spare seat post bolts and I have filed out where the head of the bolt sits so it doesn’t bend as much when it is tightened. My seat post doesn’t slip but every time I take the seat out and put it back again I get nervous doing up the bolt.
Peter
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... and on my Raven Sport Tour. Snapped the bolt. I too carry a spare bolt - which is a ridiculous thing to have to do when you think about it.
ian
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I like your solution, paulsc. Except it makes the seat easy to steal, no?
Why would it make it any easier to steal? Kevin
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I'm assuming that's a quick-release clamp, but maybe not?
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It is the non-QR version so it requires an allen. I do feel more confident about this set up and it was the only significant flaw in it's design. I hope Andy or Robin notice the replies and make some simple and inexpensive changes to their frames.
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A less expensive option is just to use an external nut, rather than the thread in the braze-on.
This can be retro-fitted by drilling out the thread in the existing fitting.
If the bolt breaks, replacement is trivial.
Ideally, you would use a nut that allows some lateral rotation, i.e. a cylinder drilled & threaded at right-angles to its axis.
This eliminates the stress raiser caused by bending of the bolt that is part of the problem.
Steel mountain bikes with QR seat-clamps sometimes use this setup.
Even a plain external nut will reduce the stress, as there will be a bit more compliance in the system.
Probably worth upgrading to a high quality stainless bolt, too.
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This seems a common problem. I was riding with some guys on a charity run last year and one had his seatpost bolt break. He was riding a Ribble. We managed to call at some agricultural machine shop and botch it with an external bolt as described by Blair. Before that he did 5 miles without sitting down and had some 60 to go so had lost all interest in preserving the threads on his frame. There do seem to be a lot of cases reported on different bikes out in googleland. Maybe it is something that needs looking at by either using stronger higher grade bolts or some sort of shim to keep the sides parallel?
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Hello
I have not yet had trouble of this nature although I have occasionally been worried about it. Inasmuch that I check the seatpost every ride and regularly regrease the post and bolt.
My own view on this 'problem' is that either the seatposts are not the perfect sixe or the person tightening the bolt is to blame for overdoing the tightness. I cannot for the life of me understand why in this day and age a simple fitting such as this cannot have extra strong bolts.
John.
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I have to admit that I too have managed to snap the seat binding bolt - indeed I have snapped two :( The first was the standard part from SJSC and the second was a security bolt that I used as a replacement (it failed very quickly). Both bolts went while they were being adjusted - has anyone lost a bolt while there were riding?
However I am also non too fond of "non-integrated" seat clamps. I find them painful to adjust - or not up to the job. So if I was given the option tomorrow to change I am unsure If I would take it.
For the record:
My bolts were adjusted to 15NM on a pre-set driver (not sure what the manual states so this might be high).
I always use coppa slip grease on my bolts.
Bike has now seen more than 16000 Miles. Both bolts failed (it was in quick succession) about 8000 miles ago.
This was on my RST - My wife's RT has never snapped a bolt
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Never had this problem, probably because I immediately installed a Pitlock - it took 20 seconds, and did not require any retro-fitting drilling.
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Never had this problem, probably because I immediately installed a Pitlock - it took 20 seconds, and did not require any retro-fitting drilling.
I agree that Pitlocks are good, although not infallible. I managed to break one of their wheel skewers through over enthusiastic tightening. I've never heard of a problem with their seat post bolt.
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Hello
I think that the 'problem' lies more in the direction of the actual machined size of the seatpost rather than the bolt itself. I suspect as I often need to tighten a seatpost bolt on one of my bikes that some seatposts are slightly smaller guage than they should be leading to 'over' tightening. I do know that when I used a carbon seatpost that it fitted much tighter than the alloy one previously used. I have returned to alloy posts as the fear of a sudden snap of a carbon one was too much a burden to worry about!
John.
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Wish I had paid more attention to this thread :-[
I broke my seatpost bolt today, I had adjusted the saddle height and was tightening the bolt, it went on for a while without seeming to get any tighter ... I was wondering if I should stop tightening ... too late, it went!
I have ordered a pack of 10 from SJSC, so should always have a spare in future.
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hmmmmm I just read this thread and had a look at my seat post bolt, it's bent. We are about to head off on our big trip in two weeks so now I'm wondering if I should take to our precious Raven's with a hacksaw and file and install a collar. We will obviously be needing to remove the saddles frequently for air trips so the risk of failure might be high.
Given the quality of the rest of the bike I'm a bit surprised at this finding. In fact I would have thought it easier to build with a collar rather than welding on the binders??? But I'm no engineer :)
Your thoughts on the hacksaw treatment for this problem.
Cheers
Gary
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Garyper,
I wouldn't rush into that decision. I do however always carry a spare bolt!
This bolt + spare chain link + spare inner tube & patches + a few tools represent the bits I keep in my saddle bag permanently.
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I have had the seat post bolt break on me three times now. It is the only thing on my RT that I am all bitter and twisted over. Last time was while reassembling the bike after flying to the start of a tour. While I did carry a spare the hard part was getting the broken end out. The break left a burred edge on the thread of the remaining piece so it didn’t unscrew easily. I am preparing myself to take a hacksaw to my frame.
Peter
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Thanks for sharing that Peter, that is exactly the scenario I would not like to experience. I'm talking with my friend who owns a bike shop here today to see what he thinks. We dont have any true bike builders here but it doesnt look that harder to cut, file and place collar on.
Cheers
Gaz
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I am thinking I will need to tape up the inside of the seat tube so no filings fall down into the tube and start to rust or get caught up with the eccentric bottom bracket in some way. Also protect the rest of the bike from the filings with some plastic sheet. I would also need to be careful with the filing so I don’t leave any thick bits or take too much out. And use some touch up paint on the exposed metal.
Peter
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Carrying a spare bolt sounds a good idea . . . . mine is not broken but looks slightly distorted.
Does anyone have a note of the part number or reference?? My bike is a Raven Tour . . . .
Thanks
Lewis
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M6 bolt, as below
http://www.sjscycles.co.uk/sessionID/JNV/product-Apex-M6-Stainless-Steel-Bolt-Socket-Cap-Head--Pack-Of-10-1840.htm
20mm version for RST
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We dont have any true bike builders here but it doesnt look that harder to cut, file and place collar on.
Further back in this thread you'll find remarks about the kind of collar that instead of a nut has a round cylinder drilled and tapped through its middle to relieve stresses. On a non-Thorn bike, either my LBS or I broke the collar itself on one of those supposed low-stress collars merely by putting in a spanner at an inspection. So I'd suggest that for a tour you don't buy the super-lightweight fitting. I'd say that anyway, because of that experience, but it is especially important if you'll be cutting and filing on the seatpost, and cannot guarantee to get it perfectly round. In fact, you might want, if there is enough seat tube above the junction with the seatstays, to use a seat collar that has twin bolts to spread the stress of a seat tube that be may no longer be perfectly round. I have a twin-bolt seat collar (which admittedly I bought for the aesthetic reason that it matched my stem...) and it not only looks good, it doesn't appear that it will ever need tightening again, whereas single-bolted collars on my other bikes, which are ali rather than steel, need checking once a year.
Good luck on your tour.
Andre Jute
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Hobbes,
I have never seen a twin bolt seat collar. Please provide a photo or a link. Sounds like it would never fail you.
As far as getting the tube round after cutting, the frame builder I took mine too completed the job in about 10 minutes and the ST was perfectly round. He fillet brazes his frames so owns a pneumatic belt sander, which he uses to sand his joints, and which made this job quick and easy for him. I wouldn't hesitate to do it myself next time but hopefully there won't be one :). After cutting off the setup with a hack saw, I would just take a 1" wide, foot long strip of the appropriate sandpaper, hold it by the ends, and sand it smooth as if I were polishing a shoe. This is essentially how his pneumatic sander worked. It might be slow going but you would have a huge margin for error, unlike a file.
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I have never seen a twin bolt seat collar. Please provide a photo or a link. Sounds like it would never fail you.
http://www.chainreactioncycles.com/Models.aspx?ModelID=40057
http://www.chainreactioncycles.com/Models.aspx?ModelID=12140
http://www.chainreactioncycles.com/Models.aspx?ModelID=8213
http://www.chainreactioncycles.com/Models.aspx?ModelID=3226
http://www.chainreactioncycles.com/Models.aspx?ModelID=45216
All of these are by definition a bit heavier than the singles, of course. -- AJ
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I have used this type of arrangment on my expr in combination with a carbon post.
http://cgi.ebay.co.uk/eXotic-6061-T6-Non-Slip-Double-Seat-Clamp-31-8-27-2-Pat_W0QQitemZ200439476918QQcmdZViewItemQQptZUK_sportsleisure_cycling_bikeparts_SR?hash=item2eab1fb2b6
I think that the other type clamps are also good as instead of a fixed nut or tapped hole in the clamp it uses a rotating barrel nut which means the bolt has no flex in it at all .
http://cgi.ebay.co.uk/Gusset-Clench-Single-Bolt-seat-clamp-30-0-black_W0QQitemZ370325128097QQcmdZViewItemQQptZUK_sportsleisure_cycling_bikeparts_SR?hash=item56391903a1
This problem comes about for a few reasons, prodomanantly when seat posts are under size, but material of post into material of frame also contribute greatly to how a seat post clamps up.