An unusual thread about an unusual thread.

Discussion in '4-Stroke Engines' started by Irish John, Nov 5, 2008.

  1. Irish John

    Irish John Guest

    I sheared one of the two M6 bolts that hold the gearbox onto the motor - I'd used too much threadlock and had to use an impact screwdriver on it to undo it and the head sheared off and I had to drill the bolt out. I found that all the gearbox bolts are 0.9 pitch thread which is so unusual that nobody in Australia makes a tap & dye of that pitch. I think all the Honda threads are 0.9mm pitch which is very unusual. I got around it by tapping a standard 1.0 pitch thread and using a standard bolt.
    I wonder why Honda use such an unusual pitch - it's almost as weird as Harley Davidson who are famous for their weird bolts.
    The lesson here is to be sparing with red threadlock!!

  2. bluegoatwoods

    bluegoatwoods Well-Known Member

    OK John.

    I've never used the stuff. But I'm bound to sooner or later. When that day comes, I'll keep this in mind.

  3. ocscully

    ocscully Member

    American SAE not Metric?


    I think you will find that the threads you are dealing with are actually American SAE 1/4-28 Fine threads, not an obscure metric with .9 pitch. I don't know why Honda uses a mixture of American and Metric fasteners on their motors but they do. The four pads that mount the motor to the mount plate are Metric 6 mm X 1.0 The end of the crankshaft for the fastener for the clutch is American SAE 1/4-28 Fine just as the four mounting pads on the left side of the motor where the gearbox mounts.

    As for the red threadlocker I've always been under the impression that it is for basiclly permanent installations and to get it to release the a good bit of heat needed to be applied?

  4. arceeguy

    arceeguy Active Member

    This is because the Honda's were engineered to work with gearboxes and clutches that were made to bolt on American made engines. (Briggs, Tecumseh, etc)
  5. Irish John

    Irish John Guest

    Thanks Oscully & Aceguy, sounds logical. The small M4 nuts that hold the on\off switch and the stock exhaust are also American threads but a 1.0 metric bolt can be used if you have to. I think it's true for the kit exhaust bolts as well which I don't use - I notice that a standard metric nut won't fit on those bolts so they must be SAE 1\4-28 Fine.
    I bought the red threadlock in a $2 Chinese shop and it didn't tell me that on the packet. I'll stick with the blue stuff in future.
  6. heathyoung

    heathyoung Member

    Never use red threadlock (permanent assembly strength) for anything you intend to ever removed - Blue is better (anti-vibration) and there is another colour - which is used as a tamper evident seal.
  7. Pablo

    Pablo Motored Bikes Sponsor

    Heat from a simple heat gun will allow you to remove any loctited fastener.
  8. n8ygn

    n8ygn Member

    helpfull hint for threadlock

    Threadlock is an anaerobic, (absense of air) to loosen quickly use heat then unscrew. Got a hair dryer it is a lot easier that way.
  9. Irish John

    Irish John Guest

    A hair dryer surely wouldn't be hot enough?
  10. bubbatgs

    bubbatgs Member

    Next time you try to remove this bolt! Try hitting it with a torch first!! If you get locktight up to about 800-1000 deg. it will act just like lube!!!