Thompson Post+CSI Seat Cluster = 1 Pissed Off Doc

[Dr. Doofus]

The Annoyed Doctor Says:

He and I have this dang self-adjusting, sort of jackassed unintentional suspension-effect Thompson post in the ol CSi.

Ride smooth roads, lovely.

Ride the crap around here and after 15 minutes the post slips down 1mm. Ride another 15 and its 2mm. Now the doc is a finicky sort and he and I sure notice that 1mm. The 2mm really sets us off.

The problem, dear Ben, is not with your bike, but with my post.

Dang Thompson posts are hard. Real hard. Many a mechanic has cursed to me about them, and how you can have ahard time finding a seat clamp that will bite down on em and make em stay.

I busted the factory bolt on the CSi long ago, an dthe doc gave me an earfull about that. My LBS found a long steel sucker that we put in there and torqued it down HARD with a T-Handle, but that post won't be tamed, I'm tellin you. And yeah, we tried other Thompson posts....

See, the doc and I need that zero-setback post. But this crap has got to stop. Now, on my Merckx we've got this Campy bolt that you get from your two sides, and that sucker holds back anything...Thompson posts, charging rhinos, Ann Coulter within ten yards of Howie Dean...anything.

So the doc has this question, because he and I know a lot about exercise physiology, something about English, and nothing about bikes:

Will a Campy bolt work in that CSi cluster????

Stupid question, I know. They don't call the doc a Doofus for nothing.

[shinomaster]

I think any binder bolt will work. I broke the piece of crap that came with my Atlanta, and have used both campy and suguino bolts with no problems.

[PaulE]

Knock on wood, I've had no problems with the straight Thompson post in my CSI.

[slowgoing]

I had exactly the same problem last week with a Thompson post on a Colnago Master X Light. Ruined the whole ride.

[David Kirk]

Yo there,

Have you looked inside the frame and made sure that there's no paint or framesaver on the inside of the clamping area ? Both are very slippery and can cause the post to slip.

Unfortunately I've seen a few problems with Thompson posts due to the lathe turned finish they use. It reduces surface contact in the clamping area and the lathe grooves hold moisture that can cause them to get sieze into the frame.

I would try a Campy post...as odd as it sounds a 27.2 post isn't 27.2 in diameter. They are anywhere from 27.13 to 27.18 so that they will fit into a 27.2 hole. anyway...Campy posts tend to run toward the larger end of the range and give a bit tighter fit.

Good luck,

Dave

[Too Tall]

Your post is not to spec. There is an ugly solution...not a terrible one but will permit you to use the post. Find a shop with a good old knurling device. Stein makes the tool. Mark your post so that the shop know where the exposed portion is and have them knurl the areas 1" below that and you won't see it.

QUIT over torquing that beautiful frame! You don't need more force...you need a correctly sized seatpost.

[DonH]

I had the same problem with the seatpost on my Merlin mountain frame. After trying a Thomson , Shimano XTR , Syncros Ti and Syncros aluminum posts I discovered that the Syncros seatposts were the ONLY two that wouldnt move. The diameters were all within .001 of an inch. I still cannot figure it out. Im using a Thomson post on my IF Deluxe and it works great though.

[tuco]

Originally posted by Dr. Doofus
The Annoyed Doctor Says:

...
I busted the factory bolt on the CSi long ago, an dthe doc gave me an earfull about that. My LBS found a long steel sucker that we put in there and torqued it down HARD with a T-Handle, but that post won't be tamed, I'm tellin you. And yeah, we tried other Thompson posts....

...



Is it possible that the seat clamping mechanism is not quite right? I had this problem on a frame twenty years ago. After breaking several Campy binder bolts, I took a look at the way the bolt and nut were seated and realized that the bolt was not seated correctly -- the clamp was "off" slightly -- so that the bolts were unduly stressed while seeking enough clamping force. I removed some metal from the lugged design and lived to ride another and another and another day.