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  1. #1
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    Seatpost Bolt Broke

    The seatpost bolt (8x1.25) on my 88 Bertoni broke for the second time. The first one lasted twenty years, the second one I found at a hardware store lasted one year. Just riding along and snap! the saddle is hanging, and I'm riding home standing the whole way.

    If I went to a higher grade bolt, say 12.8, would that help the issue? I couldn't find one at a bike store, but I could get a 12.8 at Mcmaster Carr.

    Thanks for any comments you have,

    Bob

  2. #2
    Senior Member jeepr's Avatar
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    It is definitely more difficult to break hardened bolts. I don't know what grade 12.8 is, are you in a country other than the US? If I couldn't get a seat post bolt, I would use a grade 8 bolt or better would be Stainless 18-8.

  3. #3
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    I'm here in CA. I should have said 12.9. I think it is the class of bolt in metric. I will check out the 18-8 stainless. Thanks

  4. #4
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    "18-8" stainless steel is Grade 304 stainless. It's very corrosion resistant but not strong and not heat-treatable.

    I'm surprised you broke even a standard strength bolt as an 8 mm bolt is very strong even is made from plain carbon steel. How tight are you torquing it?

  5. #5
    Bianchi Goddess Bianchigirll's Avatar
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    are you talking about the bolt that holds the seat to the post or clamps the post in the frame?
    Bianchis '87 Sport SX, '90 Proto (2), '91 Boarala 'cross, '93 Project 3, '88 Trofeo, '86 Volpe, '89 Axis, '79 Mixte SOLD, '99 Mega Pro XL Ti, '97 Ti Megatube, , '90 something Vento 603,

    Others but still loved,; '80 RIGI, '80 Batavus Professional, '87 Cornelo, '86 Bertoni (sold), '09 Motobecane SS, '98 Hetchins M.O., '09 K2 Mainframe, '89 Trek 2000, '?? Jane Doe (still on the drawing board), '90ish Haro Escape

  6. #6
    coprolite fietsbob's Avatar
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    shouldn't take that much force, is there an excessive gap
    between frame and seatpost?

  7. #7
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    I'm talking about the bolt that hold the saddle to the seatpost. I don't feel that I over tighten it. I did find a class 12.9 at McMaster Carr. It is rated at 170,000 psi compared to 100,000 psi for a standard bolt. I would have never thought it would break but, it's happen twice now. I'm sure the original bolt better than the one I replaced it with.

  8. #8
    Senior Member igknighted's Avatar
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    I had the same issue on my mountain bike years ago... snapped about 5 hardware store bolts before picking up something hardened (I really don't remember the grade, sorry... I was 16 at the time) and that solved. Still using it today, some 10ish years later.
    Road: 2011 Specialized Tarmac Comp Rival
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