Seatpost shim in Ti frame - replace, or get correct post?

[garethrl]

I'm in the process of giving my '03 Litespeed Lookout Mtn a bit of TLC, and had a fair bit of trouble getting the post and shim out. The post is an old-ish Giant carbon and the shim is marked 27.2 - 29.6.

In general, am I better off keeping the aluminium shim in there, or should I try to look for the correct size of post - bearing in mind that 29.6 is hardly the most common size? Is the original shim in there purely as a reducer, or is there any other reason too?

Finally, what would be the correct sized seatclamp for this frame? I bought a new one off the 'bay but it's far too big! If no-one knows then I'll have to buy a pair of calipers tomorrow.

Cheers, Gareth.

 

[pete_mcc]

I always thought that the shim was original to the frame, in much the same way as they use headset shims in Litespeeds. Don't they all use 27.2mm seatposts as I know the most common Litespeed post size is 27.2mm (very nice ti seatposts as well). Think the idea was to avoid Ti seatpost and Ti frame fusing by using a cheap shim.

 

[Carsten]

yes, the shim is there for good reasons. the seat tube would be too thin walled to take the stress alone. i thought it is glued in and thus not that easy to get out...

carsten

 

[SeeingisBelievingGTMuseum]

My 91 Xizang takes a 29.4 and back in 91 it was damn near impossible to find anything in that size so I shimmed and ran a 27.2 MR Ti post for four or five years before finding a lighterweight alloy post in 29.4. I never had any issues running with a shim. Stayed put just fine. What the others have said is also true if it was supplied by the frame manufacturer stick with it.

 

[garethrl]

Thanks for all the input so far guys! I did notice how thin the seat tube walls were

Carsten - that explains all the gunk on both the shim and inside of the seatpost then, and why it was so difficult to remove. It's a relief to know there wasn't some nasty reaction between tube and shim. Is it glued in place mainly to make it hard to remove, or does it further strengthen the region at all? Basically, should I re-glue it, or will it be ok just put back in place? And if I need to re-glue, then what to use?

Anyone know the size of clamp that I need for this frame, or do I need to splash for the caliper I've been meaning to buy for an age now ...

Thanks again, Gareth.

 

[garethrl]

been a while but ...

Ok getting back to this one after a delay ... I heard back from Paligap, who now import and distribute Litespeed in the UK. Their suggestion was to strip the bike down and return it to them, to then be sent back to Litespeed USA in order for it to be professionally bonded back in place. The cost would likely be around £350 :shock: quote: "... due to high costs of insured postage ... etc etc blah blah ..."

This seems rather excessive to me. Does anyone know if the shim has to be bonded in place - or is it bonded mainly to discourage removal? What's used for the bonding anyway, is it something that I could buy commercially, or perhaps something that a good bike shop or framebuilder would have?

Cheers, Gareth.

 

[hamster]

I can't see what the bonding is going to do - everyone else uses dry fit shims, and the whole lot is in compression (i.e. squeezed together) by the seatpost clamp.

 

[garethrl]

Well, as Carsten pointed out, the seat tube walls are extremely thin so perhaps the bonding might be significant, I don't know. All I know is I've never seen a shim bonded in place before and though I don't much about material science it doesn't strike me that a good, long, tight-fitting shim would need to be bonded - as you say compression should be adequate.

Unless someone better qualified says different of course ...

Do any other Ti frame builders use bonded shims?

 

[kaiser]

IIRC there is a framebuilders forum with lots of respected builders who may have a better idea or the confidence to tell you the right answer. I think it was fairly friendly too and were open to questions. Possibly saw it mentioned on weightweenies, where you could also ask as well.