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Easton EC90 seatpost slipping

Posted: Thu Mar 07, 2013 8:04 pm
by HugoDrax
Dear Weight Weenies,
I am currently riding a Guru Ti road bike with a 27.2 Easton EC90 seatpost that keeps slowly slipping down into the frame. In an effort to help keep the post in one place I purchased a Salsa LipLock seat collar, but even at 10 nm of force the post will still slide scraping little bits of carbon off as it goes. Obviously, that is not good! Initially, I just tried the Salsa clamp and Finishline carbon assembly paste. After that failed to work I went ahead and sprayed a few layers of Krylon clear coat to help build up the post so it would fit more snugly. Now after a handful of rides the post is slipping again and the assembly paste seemed to have melted the clearcoat. So my question is: what other products could I use to help create friction so the post will stop slipping? Also, it will need to be safe for both carbon and ti. Thank you for your ideas in advance!

Re: Easton EC90 seatpost slipping

Posted: Thu Mar 07, 2013 8:38 pm
by eric
Could the post be undersized or the frame oversized? You could take them to a machinist or a really well equipped and knowledgeable LBS to get them measured.

Have you been able to use a different post successfully?

I would have used clear epoxy on the post instead of clearcoat.

I have heard of Gurus with construction problems before.

Re: Easton EC90 seatpost slipping

Posted: Thu Mar 07, 2013 8:38 pm
by Weenie

Re: Easton EC90 seatpost slipping

Posted: Thu Mar 07, 2013 8:47 pm
by em3
Carbon paste will fill the gaps...apply liberally. EM3

Re: Easton EC90 seatpost slipping

Posted: Thu Mar 07, 2013 8:54 pm
by thisisatest
Grease the threads on the clamp bolt.
And it seems counterintuitive, but grease the clamp to the frame.

Re: Easton EC90 seatpost slipping

Posted: Thu Mar 07, 2013 9:52 pm
by HugoDrax
So let's see, I have greased the threads on the clamp bolt, but I did not grease between the frame and collar. Have you noticed a difference in applying grease? carbon paste? between the clamp and the frame? Also, I have used a ton of carbon paste previously, but that wasn't working. Also, I know the frame is a 27.2 and the post is as well. The frame uses a 35.0 clamp because the ti tubing is super thick right around the seat collar area for strength. I am sure that the thickness of the tubing around the seat post is making the clamp have to work overtime just to clamp normally. I can bust out the calipers if necessary, but I know that only a few (3-4) light coats of Krylon clear made the post almost not go in the frame. The clear is flaking off and I can get the post back down to it's normal size without any issues. What epoxy would you recommend? I called Easton and they couldn't give me any hints except that my previous clear coating voided the warranty... Thank you everyone!

Re: Easton EC90 seatpost slipping

Posted: Thu Mar 07, 2013 9:55 pm
by Gregorio
I would try another post.

Re: Easton EC90 seatpost slipping

Posted: Fri Mar 08, 2013 1:31 am
by dcl10
I'm not familiar with your particular frame, but I've seen some pro mechanics run a smaller clamp at the base of the seatpost so that it can't slip , KCNC also makes a seatpost grip that does something similar.

Re: Easton EC90 seatpost slipping

Posted: Fri Mar 08, 2013 3:08 am
by 113245
You could try wrapping a single or double layer of electrical tape around the clamping area on the post. Gives it a good grip and slightly increases diameter.

Re: Easton EC90 seatpost slipping

Posted: Fri Mar 08, 2013 4:13 am
by HakeemT
Try precision foil (e.g. http://www.elcometer.com/en/component/p ... r?prod=674" onclick="window.open(this.href);return false;).
I had a frame where the seattube was off-spec so the post kept slipping. A 0.05mm thick sheet of brass foil did the trick for me.

Re: Easton EC90 seatpost slipping

Posted: Fri Mar 08, 2013 3:09 pm
by eric
HugoDrax wrote:I know the frame is a 27.2 and the post is as well.


That's the nominal size. I was asking about the actual size of the parts. At this point I would measure both of them since it is obvious that one is out of spec.

I have heard of Gurus having similar issues such as slightly oversize press fit BBs.

Re: Easton EC90 seatpost slipping

Posted: Fri Mar 08, 2013 7:50 pm
by thisisatest
Greasing the clamp definitely helps, especially if the split in the frame and the clamp don't line up.
if you imagine the clamp being larger than the frame, and the frame larger than the post, its easier to visualise that, when tightening, the parts have to slide against each other to shrink in circumference.

Re: Easton EC90 seatpost slipping

Posted: Fri Mar 08, 2013 8:58 pm
by HugoDrax
Hey everyone!
So after completely removing all of the remaining clear coat I went ahead and...

1. Put friction paste between the clamp and frame
2. Cut out and thinned a Fat Tire beer can for a shim
3. Insert the clean seat post with the shim and friction paste

I am now going to go for a ride to see how it works! Thanks everyone for the suggestions and hints!

Re: Easton EC90 seatpost slipping

Posted: Fri Mar 08, 2013 9:10 pm
by eric
You should not have to shim a post like that.

Is this a new frame? Have you used other posts in it?

Re: Easton EC90 seatpost slipping

Posted: Sat Mar 09, 2013 8:25 pm
by HugoDrax
Hey, while I know I shouldn't have to shim a seat post like that the tolerance for one of the two is a bit off. I got about a three hour ride in yesterday and to the best of my measuring it looks as if the beer can shim worked out well (or it went down only a fraction of a mm). I haven't tried other posts, because I need something fairly long on this compact frame. The frame is new to me, but it has had about 100 miles on it from a previous owner. I received just the frameset and I ebayed the Easton post for the frame. Thank you all for your help! I am going to get some additional rides in to see if I fixed it or if I need to work on another solution!

Re: Easton EC90 seatpost slipping

Posted: Sat Mar 09, 2013 8:25 pm
by Weenie

Re: Easton EC90 seatpost slipping

Posted: Mon Mar 11, 2013 8:42 pm
by HugoDrax
So another update,
I used a set of calipers on the frame and post to see what the true size is looking like:

Guru frame inner diameter: 27.305mm
Easton post outer diameter: 27.127mm

Then after a bit of math it looks like the area that I need to fill will be 7.6096 square mm and the brass foil I just picked up is 0.005 inches in thickness which in a simple loop should fill 5.4328 square mm. It looks like the carbon paste will add a decent amount of space filling (possibly too much) so I might have to see about sanding down this circular piece or just cover a portion of the post. Thank you everyone for your help! I will see what this new information can do for me!