Seatpost worries

Discussion in 'Bicycle Mechanics and Repairs' started by pubrunner, 13 Apr 2010.

  1. pubrunner

    pubrunner Guru

    I'd be grateful if you could give me a little advice; I'm having difficulty finding a suitable seatpost for Raleigh which has a 753 frame and was built by the Special Products Division .

    When I bought the frame, I was told that it took a 27.2 seatpost.

    I've tried a 27.2 seatpost, but I feel that I'd really have to force it in for it to fit. I'm reluctant to do so for fear of damaging the frame. The top of the seat tube is slightly 'ovalised' - no doubt due to previous tightening of the seatpost bolt over the years. (I haven't tried to force the bolt flanges apart for fear of damaging the frame).

    I've taken the frame to a bike shop and they've found that a 27.0 goes in okay, but it might not be correct, due to the 'ovalised' effect at the top of the seatpost. ie. A 27.0 post might be okay at the top of the seat tube, but could be too slack further down.

    Should I fit a 27.0 seatpost or try a little more force with the 27.2 seatpost ?

    I'm told that 753 tubing is quite fragile stuff and I'm worried about damaging it.

    Can anyone give me any advice please ?

    Thank you !!!
     
  2. psmiffy

    psmiffy -

    Location:
    Midlands
    I have a 725 frame that I have trouble getting seat posts to fit 27.0 - I use a shimmed post - force is not the answer
     
  3. accountantpete

    accountantpete Legendary Member

    Have you given the inside of the seat tube a good clean with wire wool - it can get pretty gungy over time and this might be the problem.
     
  4. hubgearfreak

    hubgearfreak Über Member

  5. PpPete

    PpPete Guru

    Location:
    Chandler's Ford
    Combination of good clean with wire wool, a little grease, and very gentle leverage with a screwdriver between the lips of the slot at the top of the seat post. Try and avoid levering against the "eyes" where the bolt goes through. I've never broken one off, but I've seen pics.

    If still no joy - 27.0 will be fine. Sure I read somewhere (on Sheldon?) that 0.2mm difference in diameter is the maximum acceptable.

    I wouldn't want to get it reamed out. Might be plenty of metal at the lug, but this is double-butted I assume, so will be fearfully thin wall lower down.
     
  6. Gerry Attrick

    Gerry Attrick Lincolnshire Mountain Rescue Consultant

    Here's what I use for cleaning out a seat tube.

    Take a length, say about 14 or 15 inches of 1/2 inch diameter wooden dowl rod. Using a junior hacksaw, cut a slot down the rod diametrically for about two inches. Then take a piece of medium grit wet and dry paper or similar about 4 inches square and fold in half so that the non grit sides are touching. You now have doubled over piece of wet and dry 4 inches by two with grit on both sides, right?

    Folded edge first, insert the wet and dry into the slot in the dowl to the bottom of the slot. Insert the other end of the dowl into an electric drill. Now, guiding the grit paper "tails" so they trail away from the direction of rotation, feed the free end of the rod into the seat tube and turn on the drill to a medium speed.

    If you now move the rod slowly in and out of the seat tube whilst spinning the drill, you will effectively clean out rust and gunge.

    One word of warning though, if you do this with the bottom backet still in place, you must do it with the frame inverted or you risk the debris contaminating the BB bearings.
     
  7. OP
    OP
    pubrunner

    pubrunner Guru

    Cheers for taking the trouble to reply fellas - much appreciated !
     
  8. Installing the wrong seat-post, even by 0.2mm (and contrary to what the deity Shelden fecking Brown may have once thought) is a recipe for frame disaster.

    If the frame was designed to accept a 27.2 post then that is what it must have. Installing a 27 will result in your bodyweight being held only by the seat binder rather than the inside of the seat tube. And you'll have to over torque the binder bolt to get it to hold fast, inviting failure of the lug. Gently prise the back of the seat lug open with the largest screw driver you can find until the post fits. Don't be afraid, it's a common, every day workshop proceedure.
     
  9. swee'pea99

    swee'pea99 Legendary Member

    Thanks for that tip Mr Attrick, sir - I had a bugger of a time getting th seat post out of my antique 653 frame, and I wasn't looking forward to 'the return journey'. I'm sure a clean out along these lines, plus a bit of grease, will help a lot.
     
  10. gbb

    gbb Legendary Member

    Location:
    Peterborough
    If its any consolation, my Raleigh 531 seatpost was a swine as well. I made absolutely sure the post was correct with a vernier, but despite using Gerry Attricks rod and emerypaper method (which works well, i was going to suggest that)...it was simply an incredibly tight fit.
     
  11. 02GF74

    02GF74 Über Member

    I agree.

    A 27.2 mm tube should be used with 27.2 mm seatpost.

    If the frame is damaged - the ovalisation you describe - then that should be the fixed it, not by using undersized seat posts.

    Either take it to builder who can do this or else you try to fix it yourself, either by gentla prising apart the tabs or if you have the old post, put a taper (ideally using a lathe or else you can file it) on the end so it fits inside the tube, lube it then twisting the post whilst pushing it into the frame to open out the tabs, that will ensure the frame tube is formed circularly (is that a word?)
     
  12. 02GF74

    02GF74 Über Member

    when I said builder, I meant frame builder, not some oink in a white van.
     
  13. ursus_major

    ursus_major New Member

    I have a Raleigh Special Products Division 753 frame, and it takes a 27.0 seatpost. This is definitely the correct size. DO NOT force a 27.2 seatpost into it.
     
  14. OP
    OP
    pubrunner

    pubrunner Guru

    Hi,

    I'm sorry, but I blundered over my original message; the frame number is SB7953, which I think puts it at 1983/4. This means it was made at Ilkeston - the Special Bicycle Development Division (SBDD).

    The Special Products Division (SPD) was at Nottingham.

    I've since found that my bike has 753R tubing and is likely be imperial
    dimensioned tubing and hence 27.2mm - that's what Hilary Stone & Mike Mullett have told me - and they should know.

    Take a look at this :


    There is an interesting message by 'provenrad' on the London Fixed Gear Forum :

    "There was a 27.2mm seatpost in my 753 frame when I got it.
    I carried on using a 27.2 - but longer.. this is what happened:

    http://www.lfgss.com/post242277-1.html

    Further investigation by using different sized posts suggested the seattube was meant for a 27.0."

    Okay, so it wasn't a Raleigh 753 frame, but it goes to show what can go wrong; this sort of thing is something that I'm very anxious to avoid !!!
     
  15. PpPete

    PpPete Guru

    Location:
    Chandler's Ford
    FWIW I have one 531DB framed bike (that should have a 27.2mm)

    I think the previous owner was trying to fit as many "bodges" into one bike as he could. Frankly if it was a dog that had been mistreated in that way the RSPCA would have put it out of it's misery...

    Anyway it had a 26.8mm seat post in it - and the bolt overtorqued to bring the sides of "slot" almost into contact with one another.

    I've left that seat post in it because I didnt want to risk further damage by opening it up with a screwdriver.

    No disaster has yet befallen it. No signs of frame splitting, no slipping of seat-post. And I've yet to feel any sharp objects assailing my virtue...

    Given that the 753 frame in question is of considerable value to the OP I'd not be enthusiastic to use emery paper on it. Wire wool to get any "gunge" or surface corrosion out yes - but not abrading the metal. OTH a little "polishing" of a 27.2 mm seatpost might help matters in conjunction with GENTLE leverage.

    The catasprophic damage shown in those pics makes me think that's an aluminium frame. I doubt steel would fail like that whatever you did to it.
     
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice