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Thread: Found a stripped-out FD fill plug :( Repair recommendations?

  1. #1
    Registered User mneblett's Avatar
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    Found a stripped-out FD fill plug :( Repair recommendations?

    Well, in the big picture my mechanical going over of my new-to-me '88 RT has been going very well -- engine back in the frame, jugs/heads back on/etc. with no significant issues, and I'm in the home stretch.

    Until now

    I decided to fill the fluids tonight so that I can close up the tranny and put the carbs back in place -- the last step before start-up and initial break-in of the freshly dual-plugged/9.5:1 motor.

    Ah, the best laid plans, etc. ...

    I started to remove the final drive *fill* plug (I'd never touched it before this), and instantly felt that sickly, kinda "thick" feeling you get when you know that the threads are *already* stripped. The plug was basically being held in place by friction from the remains/debris of the old threads. It would rotate, but not back out of the hole (I ended up rotating it while applying pressure with a pick behind the plug head to get it to gradually walk out of the hole).

    Once the plug was out, I used the pick to gingerly remove ~6 3/4 circle rings of aluminum thread shards. Fortunately, the last thread in the hole is intact, and appears to have acted as a "wall" to prevent any of the shards from dropping into the drive housing (nonetheless, I will be checking out the internals for debris).

    So, how would you approach the repair? I haven't checked a fiche yet, but the plug appears to be 8x1.00.

    Timesert?

    Tap for a 10mm plug?

    JB Weld the plug in place and fill the FD via the breather cap in the future? (just kidding --I want to fix it "right")

    Other options?

    Thanks for your suggestions!
    Last edited by mneblett; 01-14-2010 at 04:21 AM. Reason: correct "drain" to "fill"

  2. #2
    criminaldesign
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    Hi Mark,
    A couple of the plugs on the rear were stripped when I got my 88RS as well. These have been in place almost a year and a half and works great.

    Grease was used while cutting the new plugs in place to 'catch' shavings. Afterwards flushed the rear with some easy clean and compressed air in case any shavings got past the grease. Found all pieces in garage. didn't cost a thing.

    Rear wheel check plug was replaced with a tap. I use a 5/16 wrench on the tap
    From Bike Maintenance


    Fill plug on the swing arm. Replaced with a 19mm steel bolt. cut down a bit down and strong enough to cut thread.
    From Bike Maintenance

  3. #3
    Rally Rat CATHDEAC's Avatar
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    Loctite makes a "thread repair" kit.

    I've had good luck with it... but you shouldn't "bear down" on it....


    Another option is to make a plug. Take two washers, one small enough to go through the hole... the other big enough that it can't be pushed in. put a rubber "grommet" that "just brushes" the sides of the hole between the washers and drill a hole through the rubber....Then, get a long "allen" screw.. long enough to go through the washer/grommet sandwich with room for 2 nuts.... "JB Weld" a nut on the end that is by the "smaller" washer... Run another nut down from the outside.

    Hold the allen screw from turning while you tighten the outer nut.. this should "squeeze" the washer/grommet sandwich and seal up the edge...

    EDIT.. here is a pic I lifted from this site: http://www.automedia.com/Replacing_a...cr20070401fp/1
    Attached Images Attached Images

  4. #4
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    A 1/8 NPT plug will literally screw right in because the threads are such a close match. Torque it in with only 4-6 ft-lbs so you don't crack the case and use some blue Loctite to help seal the NPT thread. Its no more difficult than that. Your hardware store will have a selection of 1/8 NPT (pipe thread) plugs. Choose the one that appeals to your aesthetics.

  5. #5
    Yarddog
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    I used some of those rubber freeze plugs to seal the pushrod holes in my engine and the speedo drive hole in the tranny when I cleaned and soda blasted them. I think that if you had to, yeah, they'd work fine, and if you stuck an acorn nut on 'em, they wouldn't be overly ugly!!! However, if you could get a Timesert, I think that would be a whole lot better than Helicoil...that is, if they make pipe thread Helicoils...I suspect do...trouble is with Timeserts, not everybody is so equipped yet...

  6. #6
    Registered User mneblett's Avatar
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    Thanks for the thoughts, folks -- one correction to my original post:

    Had a brain-to-typing-fingers fault, and typed "drain plug" -- shoulda been "fill plug" (the tiny level-checking plug on the side).

  7. #7
    criminaldesign
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    brain fart here as well.
    my 'tap' is clearly a pipe fitting. thanks for the hindsight carockwell. haha

  8. #8
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    Years ago, when this happened to me on my /6, I just took off the final drive and took it to the dealer, then they sent it to a machine shop. Labor was 50 bucks to repair it. I don't know what the machine shop did, but it's held just fine for the past 20 years. I was the one who stripped it. It's so easy to over tighten those things. I was an idgit. But, it was fun taking off the final drive, and the turnaround was 1 day.

  9. #9
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    Stripping threads in aluminum castings is very common. And my approach to repairs is to do it so it works like the original--not a temporary bodge.

    There are thread inserts available. You (or a machinist) needs to tap the hole larger to allow the new thread insert to be screwed in. Then, the plug you insert screws into the new threads, not into aluminum. And the plug and sealing washer are stock size.

    The standby is "Helicoil" which uses a stainless steel insert. A more serious approach is "Timeserts" which are a steel insert with threads on the outside and inside. Helicoils can screw in or out, causing additional problems for removable fittings. Timeserts never seem to move.

    A different approach I have used is to find a drain plug just slightly larger than the one that stripped, and cut new threads with a tap. There are also auto drain plugs with thread cutting grooves, but that's a crap shoot, since the rethreading plugs aren't nearly as well formed as a proper tap, and you might need to go yet another size larger to fix the damage. Those plugs are designed for steel oil pans, not aluminum.

    When tapping a housing, I try to plug the bottom of the hole with a piece of rag, then grease the tap to help catch the tailings. With a final drive, it's easy enough to remove it and tap upwards into the hole, or flush it after the work.

    Whether you have a stripped plug are just want to avoid one, it's important to not torque the thing too tight. I'm not sure how to describe the feel. I make it finger tight, then give the wrench a gentle tug just enough to seat the sealing washer. I suppose we could use a torque wrench, but lots of properly torqued fasterners have stripped. I just go by feel. Maybe this is a case where I can remember giving a plug an extra little oomph and feeling that dreaded uh-oh stripping of the threads.

    pmdave
    Last edited by pmdave; 01-14-2010 at 05:59 PM. Reason: typo

  10. #10
    Registered User 88bmwjeff's Avatar
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    Quote Originally Posted by mneblett View Post
    Thanks for the thoughts, folks -- one correction to my original post:

    Had a brain-to-typing-fingers fault, and typed "drain plug" -- shoulda been "fill plug" (the tiny level-checking plug on the side).
    This "plug" must freeze alot. Mine is frozen/stuck in place, and I'm afraid to apply force to get it out. I just drain it, and fill it from the top vent.

    If it were my final drive, I'd send it out to be fixed properly. And if you didn't have the final drive rebuilt, you may want to consider having the seals replaced and the threads repaired. The seals on my FD were dry and brittle when I had it rebuilt a couple years ago. Unfortunately, it costs a bit to have these rebuilt.
    Jeff in W.C.
    1988 R100 RT (the other woman)
    "I got my motorcycle jacket but I'm walking all the time." Joe Strummer

  11. #11
    TGHSMITH
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    do to the tube for the brake shaft directly behind the threads a proper repair would involve a dismantling of the final drive,,, this bolt is kind of useless, fill from the top with a measured amount of gear lube(this measurement isn't supe-critical)as for the bolt and threads , clean both up well , use a little JB weld to keep in place, fix correctly if the final drive has to be torn apart for some other reason, if you decide to fix it before hand might as well replace all the seals in the unit at that time, special tools involved...

  12. #12
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    You could make an air hose adapter for the drain plug and apply a moderate air-flow into the housing while you drill and retap the hole. Anti-seize compound on those small pipe thread fittings is a good idea as well in my experience.

  13. #13
    On the Road
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    The following is copied from my Sept. post on the same subject

    I just got through dealing with the same thing. I solved the problem by getting some of that thin white plumbers tape and wraping a few times around the bolt, then I took some white permatex thread sealant that I got from NAPA parts store and put a little of that on over the tape, then just screwed it in till just a little tight. The thread sealer dries and forms a seal in about a day or two. So far, no leaks. Quick and easy. Just make sure that the threads in the final drive and the threads on the bolt are as oil free as you can get them so you have a good seal.

    Brad

    So far, 4 months later, still no leaks

  14. #14
    BUBBAZANETTI
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  15. #15
    Alps Adventurer GlobalRider's Avatar
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    Quote Originally Posted by mneblett View Post
    So, how would you approach the repair?
    I would do it right and not take shortcuts. I don't have the time or patience to do things twice when I should have done it right the first time.

    I'd use a Time Sert or similar non-helicoil fix.

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