531 Competion seat post diameter

I recently acquired a Hewitt track bike thanks to a huge amount of help from fellow forum member Drystonepaul.

I estimate the frame to be mid 90's, 531 Competition and came with a 27.2 seat post. Is this the correct size does anyone know? It seems incredibly tight and i can't find anything conclusive through online searches, opinions varying right down to 26.8

The original picture of the bike showed very little seat post inserted in the frame - i put that down to the previous owners set up as the stem was similarly high, i really need the seat post inserted beyond the minimum level which equates to around 4". Is this a case of copious amount of grease and perseverance or does this tube set take a smaller post?

Thanks in advance for any help.

Ditto, same issue with a 531C Paul Milnes frame! I thought all 531 tubed frames were 27.2.... :?

You could try a 27.0 seatpost to see if this is a loose fit .

Nominal for an unbuilt tube is 27.4mm. Usually brazing distorts a little ovalising it to 27.2 or so. Your seatpost might well be oversize, it is not uncommon.

For what it's worth, I gave the seat tube on mine a really good clean out, and ran a needle file around it and the slot to de-bur it. With some grease on the post, 27.2 is no longer a problem...

LikeClockwork":1l08yyl4 said:

Ditto, same issue with a 531C Paul Milnes frame! I thought all 531 tubed frames were 27.2.... :?

Click to expand...

some are 26.4mm IIRC

531 is 'normally' smaller than 531c. So far, all of my various 531c frames have been 27.2 with 531 averaging around 26.8

Dead Rats":1c565lot said:

LikeClockwork":1c565lot said:

Ditto, same issue with a 531C Paul Milnes frame! I thought all 531 tubed frames were 27.2.... :?

Click to expand...

some are 26.4mm IIRC

Click to expand...

My Orbit America is 531C and 26.4mm.

I had my doubts originally, but it's all original (decals under lacquer) and I can't imagine Orbit doing anything underhand.

I did e-mail them, but didn't get a reply.

However, I do know that with the many flavours of 531, it's not exclusively 27.2mm.

I had a play around with this, this morning - tried two different 27.2 posts on the off chance one may be a little oversized - nothing doing

I've given as good an inspection of the seat tube as i can and it looks and feels as smooth as anything inside. Tried the LBS with their sizing post and they confirmed......yep, 27.2

I can only assume the top of the seat tube is slightly ovalised but i just can't get the 27.2 anywhere near it let alone where i need it to be.

The seat tube may have been deformed by a previous owner over-tightening the seat tube cluster with an undersized seatpost inserted. Any decent framebuilder can ream it out for you for a few quid if it was indeed originally 27.2mm.