To grease or not to grease

[glpinxit]

By way of explanation from a relative non-expert who has one mostly carbon bike among a small but diverse fleet and wanted to know enough to not destroy it through ignorance...

The key difference between carbon and steel or aluminium is that because it is made with fibres (carbon) in a matrix (resin) it usually has different physical properties in different planes. So you can put it under tension in one direction but may not be able to at right angles to that- depending on how the pieces of carbon were aligned. And it is generally intolerant of being crushed. Bearing in mind that a carbon frame will have been designed for lightness extra material may not have been built in to cater for ham-fisted maintenance.

This all tends to mean that you cannot do things up as tightly on a carbon bike as steel or aluminium. The seat post is a prime example. On the one hand you don’t get any problems with electrochemical reaction between an aluminium post and a steel frame which is the problem that seizes a post in a frame. But the torque required to hold the carbon post in a carbon frame without slipping may be higher than one or both can tolerate.

Assembly paste is gritty and one way of creating friction in a limited torque situation. While I do use it I’m always a bit reluctant because I really don’t like the idea that it may find its way into bearings.

An alternative solution to carbon assembly paste for a seatpost is to use a double collar. One part of the collar grips the seatpost and the other grips the frame. This is what I am currently using.

 

[Peachy!]

Re: Re:

Bit of assembly paste then. Won't hurt.

Seatpost is lacquered carbon, inside of frame is naked carbon, no shims

Just a wee point there, just so its out there, but if the inner frame is unsealed, will the assembly past bleed into or contaminate the raw carbon ? :?
Could it affect it in the long run ?.

Don’t worry about the carbon, it’s pretty tough stuff, it’s the resin that is imbedded in the carbon that is the weak point, it hates petroleum based products and extended exposure can soften or swell this resin leaving you with a stuck post. As the gang above have said, use the water based paste, you won’t regret it.

 

[rogerzilla]

You want something in there to prevent water ingress to the frame which is less serious than in a steel frame but won't be great for the BB. Carbon assembly paste is probably safest. A sachet of the pink gritty FSA stuff is very cheap.

 

[dyna-ti]

Re: Re:

Bit of assembly paste then. Won't hurt.

Seatpost is lacquered carbon, inside of frame is naked carbon, no shims

Just a wee point there, just so its out there, but if the inner frame is unsealed, will the assembly past bleed into or contaminate the raw carbon ? :?
Could it affect it in the long run ?.

Don’t worry about the carbon, it’s pretty tough stuff, it’s the resin that is imbedded in the carbon that is the weak point, it hates petroleum based products and extended exposure can soften or swell this resin leaving you with a stuck post. As the gang above have said, use the water based paste, you won’t regret it.

It was just a though

 

[mattr]

FWIW, you won't stop water getting in. Short of actually sealing it with bathroom sealant or similar. Best thing is to have a drain hole, a, lesson that a lot of manufacturers could do with beating into them with a rusty bottom bracket.

And yes, some petroleum based greases will attack the bond between carbon and resin. Most if the typical white lithium stuff that the industry uses *should* be ok, but better to be safe. If you tend to use an old pot of miscellaneous stuff for everything from bushings on your car to bottom brackets and headsets, I'd be concerned!