Viewing 9 posts - 1 through 9 (of 9 total)
  • Argh stripped main pivot bolt help!
  • ichabod
    Free Member

    Uh oh, somehow both the main pivot bolt and frame thread it screws into on my stumpjumper has stripped to the point where it doesn’t engage at all. I need a knowledgeable engineer type for some advice.. is there any way to fix it short of spending £250 on a new rear triangle and bolt kit?

    This isn’t my photo but shows the same problem although on mine, the stripped section lies at the far end of the bolt.

    Thread pitch measures 1mm. Bolt is 66mm long M12 and the head is 15mm diameter.

    Possible ideas I’ve run through so far:

    1) Buy a new longer bolt and add a nut to the end – possible problem getting the bolt head the right size to recess into the frame spacer?

    2) Attempt to re tap both the male and female thread – would this ever work? Also 1mm thread pitch taps don’t seem easy to come my in M12

    3) Use something like JB weld – I guess its a high stress position in the main pivot so may not hold

    4) Some kind of insert/helicoil on the frame plus a new bolt? Might be hard to get this in straight as the frame surface is not flat. Also an issue getting hold of 1mm thread pitch?

    Thanks!

    tjagain
    Full Member

    Should be able to get a helicoil but a insert is better if there is enough material to fit one. Then just fit a new bolt. Even if you have to strip it and take it to an engineering shop to get it done its cheaper than a new frame. A decent engineering shop should be able to make a threaded bush if one is not available of the shelf.

    IIRC and I am not sure m12 x 1mm pitch is standard metric fine

    tjagain
    Full Member

    Fresh Goods Friday 696: The Middling Edition

    Fresh Goods Friday 696: The Middlin...
    Latest Singletrack Videos
    nickjb
    Free Member

    New bolt and a helicoil will be pretty easy. The face being angled shouldn’t be an issue. M12x1 isn’t common but it is available. A quick Google shows a helicoil kit for £40 which is a bit more than you’d pay for an m12x1.75 but maybe you can find one cheaper.

    ichabod
    Free Member

    Thanks for the help.. looks like I can get a helicoil kit for around £30. Although I would be a bit nervous of doing it myself – I don’t have a bench drill so it could be tough to get the hole perfectly aligned. I’m guessing my only option for the bolt is to spring for a whole new bolt kit at £40. The bolt is hollow but with 3mm thick walls. I wonder if it would work to re-thread it down a size and use an insert rather than a helicoil?

    tjagain
    Full Member

    I would go for a new bolt – its highly stressed and turning it down and rethreading will cost something. You could rethread it with a smaller diameter but would you trust it?

    find a small back street engineers – they will do the helicoil for you. a pillar drill makes it so much easier. whereabouts are you? I know a couple of folk in central scotland who would do it

    nickjb
    Free Member

    Is the bolt actually stripped? The bolts in the picture (which I appreciate aren’t actually yours) look like the thread is ok on the one on the right, just full of the aluminium from the frame and the one on the left is worn from being used while loose.

    Drilling the frame for a helicoil will be a nervy procedure but it should go pretty straight as you are only taking a tiny bit off.

    Going smaller is an option. M10x1 might be taking too much off, maybe 7/16 unf.

    nosedive
    Free Member

    Might as well get that bolt kit, all the other bolts will probably come in handy at some point

    ichabod
    Free Member

    I got lucky – found the bolt kit on sale for £25 so Ill go with that. Going to contact the local motorbike repair place to see if they can help with the helicoil though!

Viewing 9 posts - 1 through 9 (of 9 total)

The topic ‘Argh stripped main pivot bolt help!’ is closed to new replies.