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81 XJ550 mikuni throttle shaft butterfly screws

Discussion in 'XJ Technical Chat' started by MJCXJ550, Dec 14, 2017.

  1. MJCXJ550

    MJCXJ550 New Member

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    What size are the little screws used to mount the butterfly valve to the throttle shaft? Thread and diameter size and length.
    Has anyone found a tap that size?
     
  2. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Ask Len
     
  3. 81550Seca

    81550Seca Member

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    I need to know this too. Just botched one reassembling my butterflies. Anybody happen to know?
     
  4. MJCXJ550

    MJCXJ550 New Member

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    I bought from Len. Put some locktite on and they worked just fine.
     
  5. LarryMc

    LarryMc Active Member

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    They are 18-8 thread size unsure of the length. The safest route on those screws is to toss the old ones and reinstall hex type fasteners with loctite. Len hooked me with some sweet stainless fasteners and a few words of wisdom for tackling this task. The hex drive makes the reinstall much easier.
    Remember that the Philip's style fasteners don't accept a Philip's 100% because they are JIS fasteners. (Japanese Industrial Standard) A JIS screwdriver must be used.
     
    Rooster53 likes this.
  6. MattiThundrrr

    MattiThundrrr Not a guru

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    Jis screwdrivers are tough to find, most people are unaware that they exist, but they're worth the investment. Phillips is designed to "cam out", preventing over torquing the fastener. Stripping the crap out of the head is an added bonus!
     
  7. JetmechMarty

    JetmechMarty Active Member

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    JIS tools are available at XJ4Ever. He may have the butterfly screws as well. If not, Mike's XS has the screws.

    Links to both are at VintageYamahaRally.com (shameless plug)
     
  8. LarryMc

    LarryMc Active Member

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    Screenshot_2018-01-21-09-17-52.png Len was my JIS screwdriver source. At first I thought $13.00 was kind of steep for a screwdriver but figured what the hell, "whats done is done". It is an excelent quality tool. It did the trick with the throttle shaft screws without an issue.
    Fast forward a year:
    That is now my "go to" screwdriver when wrenching and it has popped loose fasteners that wouldn't budge when attempting to use a #2 Phillips. Worth every bit of that $13.00. I'm contemplating buying a set of them.
    The above image is the brand he sells, $30.00 for the set on eBay.
     
    Last edited: Jan 21, 2018
  9. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    HCP6336 THREAD CHASER AND CLEAN-UP TAP, made from a high-speed uncoated steel. For use on all Hitachi and Mikuni throttle shafts where the butterfly valve screw on, and for the petcock faceplate mounting screw holes.
    $
     
  10. Polock

    Polock Well-Known Member

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    no they are not, because there is no such thing
     
  11. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    18/8 (or 18-8) is a grade (variety) of stainless steel, it refers to the percentages of chromium and nickel in the material:

    18-8: 300 series stainless steel having approximately (not exactly) 18% chromium and 8% nickel. The term "18-8" is used interchangeably to characterize fittings made of 302, 302HQ, 303, 304, 305, 384, XM7, and other variables of these grades with close chemical compositions. There is little overall difference in corrosion resistance among the "18-8" types, but slight differences in chemical composition do make certain grades more resistant than others do against particular chemicals or atmospheres. "18-8" has superior corrosion resistance to 400 series stainless, is generally nonmagnetic, and is hardenable only by cold working.


    The thread size for butterfly screws is M3 x .50 thread-pitch.
     

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