Thorn Cycles Forum
Community => Thorn General => Topic started by: David Simpson on August 17, 2015, 08:24:45 PM
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In the latest version of Thorn's "Mega SOLO Brochure" (http://www.sjscycles.com/thornpdf/THORN_MEGA_BROCHURE.pdf (http://www.sjscycles.com/thornpdf/THORN_MEGA_BROCHURE.pdf)), there is a section entitled "How to look after your steel frame" on page 9. In that section, Andy Blance says:
Whether your frame is Steel, Alloy or Titanium, all Aluminium Alloy seat posts and shims should be removed, re-greased and replaced before and after every winter. (Or monsoon!) This will prevent the post from seizing into the seat tube.
I'd like some clarification on what he is saying. I can see the sense in applying grease between the seat-tube and the shim, to prevent water from getting into the seat-tube. Does grease here also allow the shim to move relative to the seat-tube as the clamp is tightened? (I am thinking that perhaps the shim might stick to the inside of the tube and prevent the tube diameter from decreasing as the clamp is tightened. Does it make a difference if the cut-out gap on the shim is on the opposite side from the gap on the tube?)
But what about between the shim and the seatpost? Wouldn't applying grease there cause the seatpost to slip down while you ride, unless the clamp was tightened to an excessive amount? Or is there a non-slippery grease that can be used?
So many questions. :) My little engineering mind likes to know how things works and why.
Thanks,
Dave
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Hi Dave!
I can't and won't speak for Andy Blance and Thorn, but as a cyclist with some experience servicing bikes, I'll take a stab at answering your questions.
I've had the unenviable task of removing seized seatposts from friends' bikes. It can be horrible, as the 'posts can cold-weld themselves to the seat tube and a variety of methods then have to be employed to remove the remains of the post without destroying the frame. For what it is worth, each of the seized posts had either been put in dry, or had not been greased for decades. The bikes used in a coastal climate had the most stubborn cold-welding to overcome.
I grease mine generously with Phil Wood Waterproof Grease and have had no problems in 35+ years. I do my quill stems, also, and remove the parts and renew the grease periodically.
For my Nomad and tandem, I grease between the seatpost and seat tube and both sides of the shim. I have not found the extra grease to cause the post to slip, so long as the gap between 'post and seat clamp/shim is within specs. A too-small 'post will slip greased or dry, and will require excessive tightening of the seat lug bolt, resulting in distortion of the clamp and ears.
As for greasing intervals, annually sounds like "safe" advice it would do no harm to heed. I've done mine every couple years and had no problems, but I don't live in a coastal climate, the bikes are stored inside except while touring (though mine also did fine with Phil grease when parked outside in rain all day while commuting), the roads are unsalted here, and I used mudguards (fenders) -- all of which likely extends the service interval for me. I also cover the saddle when it is wet, and the cover usually overlaps the seatpost/seat lug interface as well.
I've found greasing the shim does reduce friction and aids it in compressing onto the 'post as the seat clamp is tightened.
I reversed the shim in my Nomad so it blocked the forward-facing kerf in the extended portion of the seat tube below the clamp. I have since put it back for no particular reason. Generous amounts of grease have served to be an adequate barrier to water entry in normal use and with the shim reversed, I thought there might have been a bit of slippage -- not downward, but rotationally when the saddle was leaned against a tree or wall -- with the Thudbuster LT seatpost. It has some fairly aggressive rings milled into it as part of the machining process. These tend to reduce vertical movement, but do little to prevent or perhaps even aggravate rotational movement due to reduced surface area at the clamp. I'm still investigating. I do observe recommended/specified torque ratings on my bicycle fasteners and also on the seatpost clamp and I have not found the presence or absence of grease alone to be a factor in the post moving downward.
One observation on shims: It doesn' take much of a surface flaw to cause them to scratch a seatpost, greased or not. There was a tiny lip at the bottom of one edge of the kerf on my Nomad's shim that caused it to scratch the original post. I simply removed the shim, gave it a couple strokes with a half-round file in the offending area, and all has been well since. The same thing happened on my tandem stoker's sus-post, which also uses a shim. Check any new shim carefully with your finger before inserting a post for the first time.
Perhaps Dave Whittle or Andy himself can clarify further.
Best,
Dan.
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The theory is that dis-similar metal corrosion can lock a seatpost into a frame permanently. Grease is intended to prevent that, although you do need to make sure your seatpost bolt is tight enough. Plus, as you note, it is intended to make water ingress less likely.
I carry a spare seatpost bolt in my bag of spares when I tour. On a lot of bikes, the stem cap bolt could function as a seatpost bolt in an emergency.
More at this link:
http://www.sheldonbrown.com/stuck-seatposts.html
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Thank-you to both of you for your replies.
What is an appropriate torque for a seatpost bolt?
- Dave
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What is an appropriate torque for a seatpost bolt?
Depends on the diameter of the bolt (5 or 6mm threaded portion) and whether dry or wet (wet torque ratings may be reduced by 4% to as much as 10%). When in doubt, look to see if the recommended torque rating is engraved or printed on a sticker on the seatpost of seat collar.
Typical ratings range from 4~6.8 Nm (36~60 in lbs) with the upper limit being maximum. Park Tools caution, Seat posts require only minimal tightening to not slip downward. Avoid overtightening
5-5.2Nm (46in-lb) seems to be the happy medium used by most.
Best,
Dan.
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Dave, I'm about to try to add to Dan's wisdom on the subject, but I will note some experience with a dry seat post:
A couple of years ago, I had an occasional and mystifying squeak/creak on my ti-frame Eclipse touring back, coming from somewhere back of the bars. I couldn't identify an obvious pattern, though it seemed to happen on the power stroke on hills, esp with the right pedal. (This meant I couldn't silently overtake riders on trick plastic bikes on a climb.)
My LBS eventually found it -- the titanium frame was flexing under power (such as it was...) and the dry seat post was squawking in protest. A good coating of regular Exustar grease fixed the squeak, though I do hear a muted version now & again.
Never had the same problem on my Raven, though funnily enough, I find I can't silently overtake riders on trick plastic bikes on a climb. I do wrap the seatpost/tube/clamp with a couple of turns of black electrical tape as a guard again moisture, after checking and lubing it each winter.
Thanks, mickeg, for your suggestion about carrying a spare seat-tube bolt.
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I find I can't silently overtake riders on trick plastic bikes on a climb.
Surprisingly, I can't do that on my Nomad either. :) But then, when I'm on my bike, I'm not in a hurry to "get there". I just enjoy the ride.
- Dave
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I use torque wrench on the square taper bottom bracket bolts, never use torque wrenches otherwise. I have one seatpost that apparently is a bit undersized because that one often slips and I need more torque on the bolt.
I wrap a piece of electrical tape around the seatpost about 5mm above the clamp. Then if I have any reason to remove the seatpost, I know exactly where to put it back. And if it slipped, I can see immediately that it slipped because that gap disappeared.
On my Nomad, I do not worry about water ingress to the seatpost, I applied some Weigles frame saver to the frame before I assembled the bike. And on the Nomad any water that gets in can easily escape around the bottom bracket eccentric. On my Sherpa however any water that gets in will stay there, so that bike I worry more about water ingress. After a very rainy tour, I took the seatpost out and could see that water had gotten in so I left the the seatpost out for several weeks so that it could air dry.
I enjoy passing people on the "plastic" bikes, but I must admit it is quite rare.
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Shim???
I have a s/h Raven Tour which came without a shim. However when I greased the post as I always do, I had trouble with it slipping. Eventually I cleaned off the grease where the bolt is, and roughened the post slightly at that point as it had become very smooth there, and since then it has stayed put. I have a feeling I'm over-torquing the bolt, though, and am terrified of breaking it. At the same time the post doesn't seem loose enough to have room for a shim. Am I missing something?
I may need to lend it to a visiting family member in a couple of weeks and am reluctant to change the saddle height now that it is behaving itself.
ETA it is the Thorn own brand seat post.
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Shim???
I have a s/h Raven Tour which came without a shim. However when I greased the post as I always do, I had trouble with it slipping. Eventually I cleaned off the grease where the bolt is, and roughened the post slightly at that point as it had become very smooth there, and since then it has stayed put. I have a feeling I'm over-torquing the bolt, though, and am terrified of breaking it. At the same time the post doesn't seem loose enough to have room for a shim. Am I missing something?
I may need to lend it to a visiting family member in a couple of weeks and am reluctant to change the saddle height now that it is behaving itself.
ETA it is the Thorn own brand seat post.
Raven Tour doesn't use a shim for standard Thorn 27.2mm seatpost.
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I worry about that seatpost clamp bolt myself! Initially the seatpost on my Nomad was slipping a bit. I started using a torque wrench so I could be a bit more precise about hunting for the sweet spot between slipping and stripping. So far 9 Nm seems to be working.
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What type of grease do people use?
When we took delivery of our Thorn tandem it appeared at first sight that the seatposts were not greased.
I contacted Thorn who advised that they were using copper slip at that time - Dec 2012.
Has Thorn changed their opinion on copper slip and now use grease instead?
Mike
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I've been using: Permatex 09128 Copper Anti-Seize Lubricant
I didn't use any very rational procedure for selecting it though!
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I used Waxoyl as there was a little rust in the seat tube. Also I put a dollop in the slot above and below the bolt, to try to stop water ingress.
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Shim???
I have a s/h Raven Tour which came without a shim. However when I greased the post as I always do, I had trouble with it slipping. Eventually I cleaned off the grease where the bolt is, and roughened the post slightly at that point as it had become very smooth there, and since then it has stayed put. I have a feeling I'm over-torquing the bolt, though, and am terrified of breaking it. At the same time the post doesn't seem loose enough to have room for a shim. Am I missing something?
I may need to lend it to a visiting family member in a couple of weeks and am reluctant to change the saddle height now that it is behaving itself.
ETA it is the Thorn own brand seat post.
Since the grease is for two purposes, (1) reduce chance of dissimilar metal corrosion and (2) prevent water from getting in the frame, on a Raven Tour you probably are unlikely to have a problem with this. The Thorn seatpost is painted, that can reduce the chance for dissimilar metal corrosion the same way that grease does that. And if any water gets in the seattube, it can drain out at the bottom bracket shell because the the eccentric in the shell is not sealed tight like a bottom bracket seals up the bottom of a typical frame.
If you are really worried about breaking the bolt, pull out the bolt and cut a slot for a screw driver on the end so if you snap it, you can unthread the remainder of it with a screwdriver. Or, instead buy one slightly longer so the end sticks out enough to get a pliers onto the end if it snaps. And carry a spare - or check to see if your stem cap bolt would function as a spare temporarily.
I have one seatpost that is a bit undersized. I have considered putting another layer of paint on it to increase the diameter slightly, I am sure only a tiny thickness would be enough. But I have not done so yet so I can't say if this is really a good idea.
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Thanks mickeg for your helpful post. I didn't realise the seatpost was painted, although now you point it out I see it is quite obvious! But in spite of the eccentric design there was rust at the bottom of the ST, so I think it was worth applying Waxoyl there. I haven't yet had the nerve to remove the eccentric, although I changed the bottom bracket cartridge itself when I changed the crankset.
Good suggestion to cut a slot in the bolt head for a screwdriver - the hole is already distorted from my efforts with an allen key :o. I'll get a spare bolt, too, though the stem cap bolt would also fit.
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What type of grease do people use?
When we took delivery of our Thorn tandem it appeared at first sight that the seatposts were not greased.
I contacted Thorn who advised that they were using copper slip at that time - Dec 2012.
Has Thorn changed their opinion on copper slip and now use grease instead?
When I bought mine (May 2012) they told me they were using copper slip.
There's some corrosion on the outside of my shim, and (where it was in contact with the shim) on the inside of the seat tube too. The corrosion made it hard to remove the seat post, as it filled up all the spare room inside the tube, jamming the post inside the shim.
A bit of WD-40 helped me get it moving, and now it's out.
I called Thorn yesterday. I didn't check, but am fairly sure I was talking to Andy. He apologised and said it shouldn't have happened. He said he greases his twice a year (as mentioned in an earlier post), either side of winter. He uses Dura Ace grease, which is very hard to clean off your hands, and he therefore considers it to be particularly tenacious. Marine grease was also recommended.
I asked about copper slip, and the chap said he's never used it on a seat post (this is the only reason I doubt I was chatting to Andy, as I'd thought it was Andy who first told me they used copper slip!). He suggested the progenitor of the copper slip idea would most likely have an engineering background.
Anyway, back on topic… there was no evidence of any grease on the outside of my shim, so once I've cleaned the rust off (with a flap wheel) I'll be greasing up the shim-to-seat-tube interface pretty liberally, then putting the post back in the shim ungreased (being aluminium to aluminium, I'm not concerned about corrosion on that interface).
From the position of the corrosion it looks as though water ran down the gap in the shim, then seeped around between the seat tube and shim. I'll be plugging that gap with grease in future…
If you've got a Thorn bike with a seat post shim, I recommend whipping the post out and checking for corrosion. It might save you a very tricky removal at some point in the future…
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I've just purchased a Mecury and replaced the Thorn seatpost with a carbon seatpost. When I removed the Thorn seatpost it had been greased with copper slip.
Id
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Maybe a year ago I had put some clear tape on my seat post right above the clamp. By now that tape got all scrunched up from slow slipping. So today I pulled the seat post out, slapped a bit more copper slip on it, put it back in where it had been when the tape was unscrunched, and put reflector tape on instead, leaving a bit of a gap so I can watch for slipping with some safe open ground between me and that dreaded scrunch.
But, ah, I see my torque wrench, but where are the hex drivers? I swear I saw them... someplace... sometime in the past few months. But right now they are just AWOL. I want that clamp bolt tight enough to avoid slipping, but not so tight that I wreck the clamp threads. That's what torque wrenches are for. But without the necessary driver... I am driven to doing it just by feel!
Tape in place, I took my Nomad out for maybe 20 miles - beautiful fall weather here in the Hudson Valley! Ah, not even five miles in, that tape was all the way at the clamp.... on the verge of scrunching! So I pulled the seat back up and snugged it down a touch more. For the rest of the ride, I watched it drift lower again and tightened it down even snugger a couple times. Finally I pulled the seat back up and seriously scared myself with my tightening. But the last ten miles didn't seem to show any further slipping. I don't think I damaged anything, but of course I have no measurement of the torque I used! Bah - if those drivers don't surface in the next couple months, I will be driven to buy a new set!
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I have a Nomad Mk2 bought 2013 and have been experiencing very similar problems with a slipping seat post, as Jimk. I have contacted SJSCycles and they recommended the Cane Creek 30.0 to 27.2 shim to replace the original Thorn 29.8 to 27.2 shim ( which appears to be no longer available). As one would expect, the new shim and post are a tighter fit and am now waiting for a break in the weather (we have two named storms due to hit the UK over the next few days!) to do test ride.
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This thread started six years ago, was resurrected a few hours ago.
At some point during the past six years I had a seatpost, painted black that would slip. A non-Thorn post. And it slipped in a couple different frames, so I blamed the seatpost, not the bikes. Slipping was not bad, but i was nervous about stripping the bolt threads or seatpost clamp threads or breaking the bolt from over-tightening.
I did not think it needed too much extra thickness, so I sprayed on a couple layers of black paint. Let the fresh paint harden up, do not recall how long, perhaps a couple weeks before using. And the seatpost stopped slipping.
I usually only grease seatposts that are bare metal to reduce the chance for dissimilar metal corrosion. I know I should grease painted seatposts to reduce water ingress, but I usually don't.
Just in case I break a seatpost bolt, on some or perhaps all of my bikes I cut a small slot in the threaded end of the bolt. That way if the bolt broke, I should be able to use a small slotted screwdriver to extract the broken bolt. Used a Dremel cutoff wheel.
On all but one of my bikes, the stem cap bolt will work as a seatpost bolt if I break a bolt on a tour.
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Just in case I break a seatpost bolt, on some or perhaps all of my bikes I cut a small slot in the threaded end of the bolt. That way if the bolt broke, I should be able to use a small slotted screwdriver to extract the broken bolt. Used a Dremel cutoff wheel.
A good tip that I saw on this forum a few years ago.
I used a hacksaw rather than a Dremel, and did all the family bikes with this type of seatpost bolt, plus one spare bolt for my touring spares kit.