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Thread: R75/5 shaft oil fill plug issue

  1. #1
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    R75/5 shaft oil fill plug issue

    Hello forum members,
    This is my first post so I'm hoping someone has some guidance on an issue I came across on the R75/5 I purchased earlier this year.

    I noticed when I purchased it that the previous owner had replaced the rear shaft oil fill plug with a 1/8" NPT pipe plug. I incorrectly figured that the plug must have been lost and that was put in as a "temporary" fix. So I recently purchased the correct filler plug and not totally unsurprisingly, there were no threads left to bite into. Are there any suggestions on how to repair this or am I looking at rear drive housing replacement? If helicoil is an option, what is the thread size on these plugs?

    Any guidance is appreciated!

    Ron

  2. #2
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    Quote Originally Posted by PARon View Post
    Hello forum members,
    This is my first post so I'm hoping someone has some guidance on an issue I came across on the R75/5 I purchased earlier this year.

    I noticed when I purchased it that the previous owner had replaced the rear shaft oil fill plug with a 1/8" NPT pipe plug. I incorrectly figured that the plug must have been lost and that was put in as a "temporary" fix. So I recently purchased the correct filler plug and not totally unsurprisingly, there were no threads left to bite into. Are there any suggestions on how to repair this or am I looking at rear drive housing replacement? If helicoil is an option, what is the thread size on these plugs?

    Any guidance is appreciated!

    Ron
    You probably have three choices.

    1) Purchase a new/used shaft housing,

    2) Drill out hole to next bigger thread size and re-thread to that size and use a larger plug,

    or

    3) drill for a heli-coil of the desired original size and put in heli-coil threads.

    In any case, you want to be careful not to get any metal shavings inside the housing.

    Also, you can purchase heli-coil kits in just about any thread desired, but heli-coils need a special tap to match the bigger hole with the older thread, and then a "insertion" tool to "screw" in the new heli-coil threads. They work great. There are other types of thread repair types other than heli-coil.

    check McMaster-Carr for some (I think they have different styles including the heli-coil brand)
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

  3. #3
    Administrator 20774's Avatar
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    It might be difficult to rethread the hole...the shaft inside is so close, more than likely it will have to come off the bike. I suppose the use of a bottoming tap could help, but you'll get awful close to the shaft. Then there the swarf as mentioned.

    There's really no serious pressure at the fill location. You can go as crude as putting a big hose clamp around the whole thing with some kind of plug. They make expansion plug that have a piece of rubber that fills the hole which then expands as you tighten the bolt on the outside.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
    #4869 DennisDarrow's Avatar
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    Once you get it done.........I really wonder of how often you REALLY need to change that oil. The book calls for changing it every 10K or so. BUT, how many times have you seen that old 50's ford pickup or whatever that is still on the road and used had it's differential changed???..........Like Jimmy or Kurt says, there is NO pressure on the plug, and, never having stripped the threads myself after MANY times of making the change, it must be fairly easy to do for someone with thick fingertips........

    That said, if one just checks that there is oil in there, or that the trans or rear end is gaining fluid, what's the need of actually changing the oil???????

    Going back to "what is original" is a pain in this particular instance, and really, who cares if that has a helicoil, new material flowed in by a welding technique, or using JB Weld and drilling and tapping new threads..............Whatever technology is available after the above very valid suggestions is what you need to do.........

    Of course you could always do as is described in the BMWMOA news this month and put in a whole new driveshaft that is lengthened and machined for a "smoother" cushioned shift...............God bless.....Dennis

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    Thanks for everyone's feedback. It sounds like there's no permanent quick fix that doesn't hold the potential to make things worse. I guess I'll leave the pipe plug in there for now and if I ever have the need or the urge to pull apart the driveline, I'll fix it then rather than risk a bout of "shipwrights disease".

    Ride safe!
    Ron

  6. #6
    FKA "woodnsteel"
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    You might be able to find an "oversize" plug. This is a part where the thread pitch and nominal size conform to OEM, but the actual threads are oversized. I used an "oversized" piggy back plug on the drain plug of a 4 speed transmission a few years ago. It worked perfectly. I centered it in the boogered up hole and carefully screwed it in using a box end wrench. The oversized threads will usually take up in whats left of the damaged threads in the hole.
    1973 R75/5
    1978 R100/80/7
    1988 R100RS (available)
    1981 R100R (organ donor)

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