KH24 Frame Too Tight for 27.2 post?

Anyone ever had a KH24 frame feel way too tight for a KH 27.2 pivotal post.

Just got a new frame from via family in Czech and worried it’s a duff frame as I have applied a good amount of grease but have had to try and twist it in hard to get it to go down even to the notch hole.

I know I can try and sand post a bit but this seems odd. The post fits my KH29er frame.


Check if the seat post is actually round – I got a Mad4One recently which wouldn’t go into my KH26 frame. It turned out that the seatpost extrusion is not actually round, it is most evident looking at it end on and the hole up the centre isn’t concentric. When I looked I saw the same on other bits of seatposts I have sawn off in the past (in my scrap box) including (I think) a KH one.

I didn’t say to Mad4One about it since I had cut it by that time, I was just going to skim it on the lathe to true it up (shame it messes up the nice anodising) but haven’t got round to that yet as I used a KH adjustable one I had instead. I realise that a lathe probably isn’t an option for you, hopefully you can fix it up with a file or a sander.

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Thanks so much for this. I did manage to get it in in the end with sand paper on the post. But I think it was more the frame seatpost stem being a bit think or ever so slightly warped. I can’t fully tell.

Seat post went into a KH29er fine. But the post from the 29er also wouldn’t in the 24. So it seems the KH24’s post neck was a bit think.

It’s in now and I’ll try not to worry about the cause.

Cheers again!

Any chance the seat clamp was restricting it (ie. Not completely loose?)
Or any bit of metal poking into the frame?

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Sadly not that no, the clamp was loose and even when off the post was a nightmare to get in.

Smooth in the inside as brand new. Perhaps that’s the issue it just needed some wear to file the ID of the unicycle’s seatpost holder.

Post was fine as went into my KH29er, so it’s either a slightly too think KH24 holder/stem or it was slightly off to a very subtle angle making it harder for the post to slide in.

Odd and a bit disappointing for a brand new frame - but there’s bound to be some margin or error in all manufacturing of these items.

Thanks for the suggestion and help!

Since you’ve got a lathe, what you can do is only turn the part that you insert. That way all damage to the anodizing is hidden. What I’d be wondering about is the first inch or so that you have to clamp in the chuck, but I’d suspect that a couple minutes with a bastard file or a disc sander can fix that.

Yes, I think the first inch or so goes in before it sticks so I can probably get that in the chuck and maybe put a fixed steady at the other end. The alternative is to hold the head of the post with a 4-jaw chuck and put a steady in the middle. I’ll need to look at it again, maybe just rotating it against a sanding disc might do enough.

Either way it spoils the finish. I’ll limit the length I do but I want a bit of adjustment up and down. If it weren’t for the fact I had cut it, and I didn’t know what was involved with returns to Italy post-Brexit, I should have just sent it back.

I’ve had this on a selection of unicycles - the process of drilling and slitting of the frame tube seemingly often warps it slightly. Used frames do tend to be much worse as the clamp has been compressing it too.

@DrD, your cutting of the post does not change the faulty construction of the product and should not in any way limit your ability to send it back.

It’s not like they should be selling it on to someone else if it’s the construction at fault. Email Marco and see what he says. It could well be that they are not aware and need to have some words with their tube supplier.

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Yes you’re right, I should really email Marco about it.

I did intend to do that at the time, life gets in the way though; I just fitted my adjustable KH one at the time and forgot about it all thinking it would be easier to just fix it up myself rather than deal with sending stuff back (a personality trait…) – unicycle seat posts weren’t really at the top of the priority list. However it is not a cheap seatpost, and as you say, it might be an issue with the tubes in general. Just to be clear, I have no issue with Mad4One, I really like their stuff.

I’ve had that happen to old frames that were shipped with a clamp on too tight.

The easiest solution would be to check with your local bike shop or machine shop if they can ream the seattube. Most bike shops dont have reamers, but some do. Local machine shops could have adjustable reamers. Alloy frames can be done by hand. I ream all my frames to 27.4mm ID so the post can slide in and out easily without scratching.


Does it look like this and did you measure it with a micrometer? I believe this is an old KH post and it is perfectly round according to the micrometer.

Pretty much – the one on the left is a KH 25.4mm pivotal seat post and the one on the right is the Mad4One XXL I was talking about. As you can see, this KH one is similar to your one internally (I have other KH offcuts where the inside is perfectly concentric). The Mad4One centre is more round, just offset a bit.

However, the KH one has around 0.02mm variability in its diameter (rotating it in a pair of digital vernier callipers not measured with a dial gauge). The Mad4One has a bit over 0.1mm variation not just on roundness but also along the length – the maximum is just over 27.3mm.

So 0.1mm isn’t much but it caused it to bind in my frame whereas two KH seat posts I tried fitted fine. Reaming it to 27.4mm as Jakob suggests would probably sort this out for me and I don’t need to mess up my nice M4O seat post. So in this case it is probably a combination of the frame and the post that caused it to bind. As I recall it started to bind when it was in the frame a little bit beyond the slot.

Oval inside is normal, it puts more material in the direction of the stress (stiffer post and lower weight). Older KH posts were round inside and out.

The non-concentric M41 is weird, probably worth mentionning to @MAD4ONE, but it’s not dangerous to ride. Worth mentionning so he can make sure the next batches are concentric.

About my reamers, I have fixed reamers of different sizes and they are all .2mm bigger than the seatposts that are mean’t to be used with. I use a big tap handle and do all of my frames by hand. It’s a good workout on a freshly built frame as I am going from 27.2 to 27.4mm. On a ‘‘ready to ride’’ frame there should only be some cleaning needed, it shouldn’t take too much effort :slight_smile:

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That’s good information, thank you.

I have a big adjustable reamer in a box of stuff we acquired a few years back – I’ll dig it out and see if it is big enough, I have something in mind that it was pretty blunt though – that would make it a bit more of a workout! Looking around it seems these things are not so expensive as I thought they might be though.

Thanks again.