Oil drain plug stripped. Any tips?

Discussion in 'Thumpers' started by Camas, Sep 24, 2006.

  1. meat popsicle

    meat popsicle Ignostic

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    I will check the drain plugs to see if they specify, but it seemed like from posts above it would be unwise to use fine threads unless the material it is "plugging" is thin. Anyways, I would rather not put fine threads in an aluminum case.
    #41
  2. JAFO

    JAFO displaced Jeep guy.....

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    well I'm not a machinist, and I would probably agree with regards coarse threads over fine, just wanted to mention that I've seen both. :shrug:
    #42
  3. OldPete

    OldPete Be aware Supporter

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    In aluminum coarse threads seen to last longer than fine threads for something removed and installed as often as a drain plug. I like the NAPA adapter pictured in this thread. I will remember that.

    Important: Re-tapping the drain hole, caution should be taken to be sure the tap is perpendicular to the gasket surface otherwise the drain plug will drip or even worse, leak a bit. If this happens a thick nylon gasket will offer a good seal but must be replaced with each oil change..or so it seems to me.
    #43
  4. Camas

    Camas Rooster Bastid

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    I'm no rocket scientist like the rest of the people that have replied. I've only had personal experience with retapping a stipped out drain plug and what worked for me. NAPA has the the over size in stock with the associated drill bit and tap for less than $20 bucks OTD.
    Good luck and hope these guys don't talk you into a cappachino maker in the process.:lol3
    #44
  5. eaglemike

    eaglemike Been here awhile

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    There isn't enough room in the KLR650 for a timesert. This is one of those cases wehre the shoulder on the time-sert isn't the best for a certain situation. With my curent monitor settings I can't see the edge of the case. If you can't see it LMK and I'll post another pic. CAn you see how thin the cross section is on the near side?
    [​IMG]
    all the best,

    Mike
    #45
  6. JAFO

    JAFO displaced Jeep guy.....

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    why do you hate cappucino?
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  7. meat popsicle

    meat popsicle Ignostic

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    I hate that almost nobody seems to know WTF it is... I order a cappuccino for me and a latte for Mrs. Popsicle and I get two lattes. :bluduh

    Oh, I will have to try NAPA because the two parts stores near me only have 1/2x13 taps, which are the fine threads eh? I am trying to stick to coarse threads while I tap out my ~stripped 12X1,5mm drain hole. Hopefully NAPA has a better selection of drain plugs because I would like to find one with a magnet like my OEM plug.
    #47
  8. JAFO

    JAFO displaced Jeep guy.....

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    OEM plug doesn't have a magnet.

    Go to Advance Auto- they have magnetic-tipped plugs in every size. Failing that, drill yours and epoxy a magnet in.
    #48
  9. meat popsicle

    meat popsicle Ignostic

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    Mine does (different bike).

    I will check out Advance if you can say they usually have the proper taps (1/2x20 - not 1/2x13).
    #49
  10. MF1A

    MF1A Ride with the Wind

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  11. cwc

    cwc . Supporter

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    1/2-13 is course thread, 1/2-20 is fine.

    The numbers 13 and 20 specify the number of threads per inch, so the lower number is "coarser" then the high number.
    #51
  12. meat popsicle

    meat popsicle Ignostic

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    Thank you for the info and explaination.

    So in order to get 75% threads what is my drill bit? The only recommendation I find is 27/64, so I guess I need to find one of them. Of course the original recommendation on Page 1 of this thread was to simply tap out the stripped 12mm drain plug hole with a 1/2x20 so I guess I don't need to drill... agreed? (note the 1/2x13 or coarse thread tap will be substituted for the 1/2x20 fine thread tap)
    #52
  13. eaglemike

    eaglemike Been here awhile

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    Standard acceptable thread is often 65 percent. A common rule of thumb that will work would be the nominal diamter of the thread minus the pitch equals the hole diameter.

    Example: 1/2 X 20 thread. Nominal diamter is 1/2, or .5 inch. Thread pitch is 20 per inch, so 1/20 = .05, right?

    .5 minus .05 = hole size of .45

    For metric: M6 X 1
    6mm minus 1mm equals hole diameter of 5mm

    IMPORTANT NOTE : this is for cut taps! Form taps are a different hole size than this formula, before tapping.

    This will work well for pretty much any situation you run into on a motorcycle. Sometimes there are special requirements for quite a bit larger or teeny sizes - but this will work. Handy to know when you don't have a chart handy.

    Anything over 1.5 diameters of thread engagement is more than plenty - again a general rule of thumb. Example: 9mm of threads engaged for a 6mm bolt is generally considered enough.

    Conversion for those that don't know -
    25.4mm per inch, or 1/25.4 = 1mm

    all the best,

    Mike
    #53
  14. cwc

    cwc . Supporter

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    If you google "tap drill size" you will get a lot of info. Here is one that does inch and metric. http://www.newmantools.com/tapdrill.htm#callink

    If you have a stripped 12mm thread now you essentially have a 12mm hole.
    12mm is .472 inches.
    27/64 is .421 inches.
    29/64 is .453 inches.

    Your effective hole is already oversize for both a 1/2-13 and a 1/2-20, but a 1/2-20 would probably be OK if there are enough threads engaged. I would like to have for at least 3/4 inch in the tapped hole. I suspect you don't have this. I don't recall seeing what bike this is for.

    I haven't used one (I only strip threads on simple to repair stuff like BMW cylinder studs :D ), but an oversize METRIC drain plug seems like a good idea to me.

    I googled "metric repair drain plug" and got this http://www.cgenterprises.com/drain_plugs_oversize_repair.htm

    I think you want a single oversize.

    A magnetic plug is about $3 plus shipping. You might be able to find one locally.

    You could look further and also google "oversize...."

    Just be sure that whatever you use you put it in exactly perpendicular to the crankcase surface. The threads alone won't seal. The seal is between the flat surface on the crankcase and the underside of the drain plug hex.

    It will likely be much easier to get the oversize plug in straight than to tap a hole straight because the plug starts in the original threads.

    BTW, if I were doing the oversize plug, I'd buy two and carry the spare because there is no guarantee that you will be able to easily buy another when you drop it and it rolls down a drain while you are changing oil in a Walmart parking lot.
    #54
  15. meat popsicle

    meat popsicle Ignostic

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    Did some research: "form taps" meaning roll (or thread) form(ing) taps" eh? I read HERE that the metal tends to spring back more from their cutting than with cut taps so there was a recommendation to use a slightly higher "H limit", whatever that means... :D probably beyond the scope of my knowledge needs but thanks for the heads up.

    Unless you feel that a roll form tap would be less likely to introduce metal into my engine. I think a machinist would consider this like a "blind hole" since I do not want to push cuttings into my engine case. I was going to use a heavy grease while taping to help capture the cuttings, and take it easy during the process. But aluminum is supposedly appropriate for thread forming (roll form tap), I just know nothing about it.
    #55
  16. meat popsicle

    meat popsicle Ignostic

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    Good points; thanks for the easy math (I didn't think to check the suggestion that way). So my 12mm stripped hole will give me something less than 75% threads with the coarse thread 1/2 (x20), making it a weak fastener setup eh? Perhaps more likely to strip out in the future?

    I'll take a look at the oversized metric plugs, which I believe you are saying could be used directly on my stripped out 12mm hole without tapping?
    #56
  17. cwc

    cwc . Supporter

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    You could search a bit and see if you find any negatives to using the oversize plugs, but I think the car guys have been using them for a while.

    Even though I have taps for most sizes and could tap the hole for a 14 mm plug, I think if I had this problem I'd go with the oversize.
    #57
  18. Camas

    Camas Rooster Bastid

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    I knew it! You guys are rocket scientists! I need a nap. :huh

    Thanks for learnin' me up.
    #58
  19. meat popsicle

    meat popsicle Ignostic

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    :lol3 I think they are machinists, which I have found to be quite a complicated art from my short reads searching for info on the web.

    Thanks to y'all for chipping in here :beer
    #59
  20. eaglemike

    eaglemike Been here awhile

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    When using form taps it's more critical to have a proper sized hole, and more critical to have the tap square to the hole. Another problem is the hole needs to be about the same depth for more than the length of the fastener, in this case the drain plug. The KLR is a perfect example of why a roll or form tap isn't a good idea - one side of the hole has less than half the depth of the other side. Since it takes pressure to form or extrude the material to make the thread, the tap will try to go sideways due to the different pressure, pushing away from the deeper side. Take a look inside the hole in your case(s). If the hole is about the same depth all around a roll or form tap is a good idea - but be sure the hole is the proper size before tapping. I always cheat and look at the chart before form tapping, since I usually do several parts when I use that method. IIRC the formula for form tapping is .5 X pitch less than the nominal diameter. Ex: M6 X 1, 6mm minus .5mm equals a holes size before tapping of 5.5mm. This gets smaller due to the material movement during the forming process.

    Sometimes I use a guide to keep the tap straight.

    I've helicoiled a few KLR drain plug holes. Even though the hole was stripped, I still had to drill it out just a bit to get it to size so the tap would start. So double check to be sure the hole will work - if the tap won't start easily, don't fight it - drill the hole.

    Form tapping is really great for some situations. It does take more power to turn the tap, too. Blind holes are about the best reason to use a form tap. meat popsicle, you're right! It's also a pain to get the chips from a cut tap out of the hole, when it's a deep blind bottomed hole, so that's another reason.

    I personally wouldn't worry about less than 65 percent of threads in the hole. It's just a drain plug. It needs to keep the drain plug in place, and nothing else should be pulling on the drain plug - it's not a structural part.:D If the crush washer has been used before I'd suggest no more than 75 percent torque.

    Sorry to be so long winded - trying to be clear and provide useful info.

    all the best,

    Mike
    #60