mrv 

Picked up this lovely 89 Panasonic MountainCat from a fellow BF member.
The seatpost is 26mm. I think original. The catalog doesn’t say.

To make sure the seatpost doesn’t slip, should I file that spot where the collar is touching?

I don’t want to create a new problem. Like a cracked collar.
I don’t believe a 26.2mm would fit.
Thanks.

sweeks

You could relieve the "close contact" with a file or Dremel disc, but if the seatpost stays put, why mess with it?

KerryIrons

Making the critical assumption that indeed you have the right seat post diameter, then filing off that bit of the collar that appears to be touching is an appropriate step. An obvious question is how that thing got bunged up like that.

Andrew R Stewart 

By using the darn QR lever too often Unlike an axle and drop out where all the parts are very solid/rigid, the seat lug often has hollow ears and the metal is usually not a very strong type. So the lug deforms a tiny bit with each clamping. Add in an aggressive clamping a few times and this result is not uncommon. If the post is steel it can slip more easily, so more clamp tightening is the first effort to keep the seat in place. The last bit is the fit of the post. I would suggest trying a one size larger one just to be sure one has the snuggest fit possible yet still be able to move the post when wanted. If the OP doesn't need to move the seat height after a correct positioning I would ditch that QR for a common bolt. Andy

mrv 

Thanks everyone
I will follow Andrew R Stewart advice
Kalloy make a 26.2 post, and I was planning to use aluminum eventually- to get away from the pipe clamp style seat attachment.

I already stuck some tape on the seatpost to see it is slipping, or I’m imagining things.

sweeks

Andy always gives good advice!
Before you purchase a new seatpost, it might be a good idea to take the bike to a shop that has a seatpost sizing gauge. Then you'll know if a 26.2mm post is the right size. An alloy post tried-in on a steel frame will probably be marked up and not returnable.

Andrew R Stewart 

I usually advise to take the bike to a shop and have them do the post fitting. For a few reasons- If they scratch a post then it's on them. If they feel that there's a burr inside the seat tube (often at the end of the binder slot or about the vent hole to the top tube) they should have the tools (flex hone, reamer) to address that. Many shops have a collection of old posts in increasing steps oif size. Note that this is not a sizing post, which I have too. The reason why I didn't suggest a sizing post for the testing is that it won't have more than a inch or so of insertion amount per step. Often a burr or distortion is deeper in the ST and the sizer post won't reach the problem spot to show it till the nice new post is slid in. And yes, this service by a shop should be worth a small cost, less than a new and now scratched post costs Andy

sweeks

Thanks, Andy! There are always more reasons than my limited experience can account for.

mrv 

Biked to church this AM and it slipped right away.
Adjusted up and tightened, but a longer ride after church was just more slipping, but slower.
I’ll visit my a LBS Tuesday & get it sized.

mrv 

Picked up a new 26.0mm Kalloy post from my LBS. The budget oriented Kalloy has those machining grooves from turning the post to the spec diameter. That’s good for preventing slipping, I think.
Got home and the post doesn’t want to fit. The seat tube doesn’t look so round, so I miss used a screw driver and hammer to persuade the tube to more roundish
​​​​​​ The post is now a slip fit- so I’m kind of hoping I don’t really need a 26.2mm. I’m sure I don’t. Maybe.
Couple of test rides and everything stayed where I wanted it. Going to switch to a binder bolt and get rid of the QR.

I’ll update again if I end up with a 26.2mm post. Probably I’ll do a while PanaCat Project thread, since these bikes Seem rare ish.

Mr. 66

I would try size up post(s) until I get one that doesn't fit, then drop down to the one that does.