Seatposts and grease

[Donerol]

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  . I'll get a spare bolt, too, though the stem cap bolt would also fit.

[gma]

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…

[High Moors Drifter]

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

[JimK]

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!

 

[UKTony]

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.

[mickeg]

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.

[martinf]

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.