Gear Oil Plug Size | FerrariChat

Gear Oil Plug Size

Discussion in '308/328' started by moysiuan, Feb 8, 2020.

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  1. moysiuan

    moysiuan F1 Rookie
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    #1 moysiuan, Feb 8, 2020
    What is the size of the gear oil plug, the one horizontal on the back of the tranmission case that you let the oil flow out to determine the fill level? I corss threaded it, and want to chase the threads with a tap, but what size? I think it is 1.5 pitch 21mm size, but I want to make sure as I will have to buy the correct tap.

    (Mondial 3.2/328 Engine)
     
  2. miketuason

    miketuason F1 World Champ
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    #2 miketuason, Feb 8, 2020
    Did you cross thread the plug or the hole?
     
  3. moysiuan

    moysiuan F1 Rookie
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    #3 moysiuan, Feb 8, 2020
    Worse than I thought, the hole is stripped, threads shot. oh boy
     
  4. moysiuan

    moysiuan F1 Rookie
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    #4 moysiuan, Feb 8, 2020
    The casing hole has good threads deeper in. Is there are longer reach threaded plug available somewhere, still not sure if it is a 21 or 22mm plug size. The washer is 22mm, my
    crappy micrometer measures at the threads 21.5mm
     
  5. conan

    conan Formula Junior

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    #5 conan, Feb 8, 2020
    I measured M22x1.5 and 15mm depth.
     
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  6. moysiuan

    moysiuan F1 Rookie
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    #6 moysiuan, Feb 8, 2020
    Mine is 13.5mm depth in total from the head to end, about 9mm of thread and taper under the head.
     
  7. Rifledriver

    Rifledriver Three Time F1 World Champ

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    #7 Rifledriver, Feb 8, 2020
    Last edited: Feb 8, 2020
  8. moysiuan

    moysiuan F1 Rookie
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    #8 moysiuan, Feb 8, 2020
    Thank you, yes this looks unrepairable engine in the car. Only hope is a deeper plug, thanks for the link.

    Stupid thing to have done, might have crossed it last time I changed gear oil and only seeing the consequence this time with the thread damage.
     
  9. SJP 5

    SJP 5 Karting

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    #9 SJP 5, Feb 9, 2020
    QV at Ascot UK can supply the longer plug as this is quite a common problem.
     
  10. moysiuan

    moysiuan F1 Rookie
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    #10 moysiuan, Feb 9, 2020
    Last edited: Feb 9, 2020
    Thank you SJP5, I am feeling pretty stupid to have done this, must have crossed a little bit at a time during gear oil changes over the years and this time it wouldn't start in the hole correctly and in the end I crumbled the transmission casing threads completely, you only know this has happened after the damange is done and plug turns in the hole. Having just done a really successful shift shaft seal replacement, I would have never guessed I would be beaten by a drain plug!

    I Amazon'ed a Dorman plug that came in today (amazing to get that fast a delivery, especially in Canada), and it may do the job. For posterity, the correct plug is definitely M22, 1.5 thread pitch. The stock plug has 10mm of reach under the plug head. The Dorman has 18mm. The Dorman has a normal bolt style with a 19mm socket head, rather than the stock allen key style. Bell Metric has one a bit shorter than this, with the allen key, and about 14mm reach from under the head, which might solve for those who have not completely stripped the out the hole. Frankly seeing what I see in the hole, the longer reach on the fill level drain plug would have made most sense and would probably have reduced the chances of stripping, there is quite a thick transmission casing threaded to spread the load and minimize the issues associated with overtightening. Would be good for the fill plug as well. Although the casing there is thinner. The gear box pan would not be thick enough to benefit from a deeper reach plug. But if you strip the pan least you could remove it and do a time sert or other type of repair. The one I stripped would not be repairable with engine in.

    I am now tempted to put the plug in, but as Rifledriver noted, I could end up not threading the new one properly beyond the damaged threads. I have ordered a 22mm tap that won't arrive for a few days, and I think it best to chase the hole and give the new plug the best chance of starting the threads where the old damaged ones end and reduce the risk of further damage.

    Picture attached comparing the stock plug to the Dorman plug. Dorman part # 090-055. Comes with a fibre washer, any reason why I would not use the fiber washer verses the stock copper one? Looks like it would use even less torque to seal, maybe a dab of hylomar, and that would do a safer job than the copper washer, especially in my more delicate repair instance?

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  11. conan

    conan Formula Junior

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    #11 conan, Feb 10, 2020
    I would be very careful with tapping the threads since there is a risk cross-cutting the undamaged threads. It is like cutting through butter (almost).

    Somehow you could try and scrape out the old threads first since they should be loose anyway. With a prepared sanding cylinder with a stop 10mm, it could be possible to get rid of any debris and aluminum ridges of the old threads.

    Being careful with this, you will be able to catch the good threads and still be able to helicoil it later on.
     
  12. moysiuan

    moysiuan F1 Rookie
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    #12 moysiuan, Feb 10, 2020
    Thank you for the important advice, my 90 year old Dad cautioned me as well, no substitute for experience. Cleaned up the damaged threads, it had mostly been cleaned up by the old plug turning, so really just removing a bit of debris. I was able to use the new plug, threading it in very carefully such that it is properly and well seated, there is lots of threads in that hole, just needed to catch them properly. I used the copper seal with some Hylomar on it, so good to go.

    Will have to be extra, extra careful in future gear oil changes in replacing that plug.

    Thank you all for the responses and coaching on this mishap.
     
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  13. SJP 5

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    #13 SJP 5, Feb 11, 2020
    Great News
     
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  14. mike32

    mike32 F1 Veteran

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    #14 mike32, Feb 11, 2020
    if you do have to tap out the thread then put some grease on the tap to stop the swarf getting into the box. Just keep removing and cleaning the tap. Works fine.
     
  15. miketuason

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    #15 miketuason, Feb 11, 2020
    Just a thought, would a helicoil be better? I've use them on spark plug holes and they work great.
     
  16. moysiuan

    moysiuan F1 Rookie
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    #16 moysiuan, Feb 11, 2020
    There would not appear to be enough clearance to use a drill to ream out the hole and do a helicoil, with the engine in the car. Engine out, for sure a helicoil or even better a time sert would be the way to go. The constraint was how to deal with the repair with the limited clearances with the engine in.

    My larger threaded plug depth solution was absolutely successfull though. I would suggest people replace this plug and the fill plug with the slightly longer Bel Metric version, that would lessen the chances of stripping the threads. Won't help with crossing threads, but it is probably a combination of overtightening and crossing that caused my problem.

    I change my gear oil every two years, so the plug gets removed fairly frequently. Maybe this also gives me an excuse to not change the fluid for a much longer interval. I use Redline MTL, and I read the sheer strength degrades over time, and being the lighter weight gear oil I thought is prudent to change it out as a bi-annual routine. But probably overkill, and sometimes leaving things alone is in fact the better maintenance approach.
     
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  17. ClydeM

    ClydeM F1 World Champ
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    #17 ClydeM, Feb 11, 2020
    If you would, add this to the xref sticky thread + RifleDriver's Ducati mention.
    Good info to retain.
     
  18. Il Steeg

    Il Steeg Formula Junior
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    #18 Il Steeg, Jul 27, 2022
    Thank God For This Thread!!!

    I just took out my transmission filler plug today ('88 Mondial), and the plug felt odd as I was removing it. First time for me on this car....Very tight at first, then loose for a bit, and then very tight (requiring the wrench) to finish. Didn't really think much of it until I went to put the plug back in...

    Then I saw it... The thin wisp of material from the trans housing - curled up like a spring - lying on the floor of the garage... CRAP! I'm starting to get a little panicky at this point... Sure enough, the plug goes in, and when it should be 'snugging up,' it just starts to spin..... SH*T! SH*T! SH*T!, etc.....

    After I'd had a while to think about what the hell I'm going to do, I think to myself, "This couldn't be the first time this has happened to someone... WWFCD? (What Would F-Chatters Do?)"

    And here you all are - F-Chat to the rescue!

    Hell, if the parts I ordered (thanks also for posting part numbers/URL's!) arrive early enough on Friday, I could have her buttoned up and ready for the Car Show this Saturday!

    Thanks again, everyone!
     
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  19. Ricambi America

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    #19 Ricambi America, Jul 28, 2022
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  20. s219

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    #20 s219, Jul 29, 2022
    That looks like a godsend for anyone who runs into the problem.
     
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  21. Il Steeg

    Il Steeg Formula Junior
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    #21 Il Steeg, Jul 29, 2022
    Good to know.....

    However....

    For me, I've hit a stumbling block...

    I ordered the Dorman parts, and they arrived this afternoon...

    I could post pictures, but as mentioned above, in the first part of the hole, where the damage is - looks fairly clean, like the threads are just gone... However, when I go to thread in the new plug, I get a definite feeling that the new threads are catching onto something. I've even tried - after getting the threads started, pulling backwards as I continue the threading process, and the Dorman plug definitely does NOT want to just slide out.

    I can thread it by hand until the point where there is just about 3/16ths of an inch left to tighten (on the threads of the replacement plug), and then it just stops. I can put the ratchet on it, but unless I use a bunch of torque (which I know NOT to do!), it does NOT want to go in any further.... I've tried backing out and restarting dozens of time, hoping to catch what's left of the 'right' thread, but it always stops at the same place... The threads on the Dorman plug still look clean and undamaged at this point.....

    I have not tried to remove any of the original damaged threads yet... I've got a Dremel tool with sanding cylinders that look just perfect for the job, but I cringe at adding any metallic powder to the gearbox that might get in as a result of getting rid of any damaged threads....

    Any suggestions/coaching would be greatly appreciated..!
     
  22. Il Steeg

    Il Steeg Formula Junior
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    PNW-In a van, down by the river.....
    #22 Il Steeg, Jul 30, 2022
  23. mike996

    mike996 F1 Veteran

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    #23 mike996, Jul 30, 2022
    Are you sure the plug you ordered is the correct thread? The Ricambi plug will certainly be. Otherwise you will need to run the correct size tap into the existing threads, which may be buggered up a bit at what is now the 'beginning' of the good threaded portion.
     
  24. Il Steeg

    Il Steeg Formula Junior
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    #24 Il Steeg, Jul 30, 2022
    It's the same one mentioned above (back on Page 1 of this thread). M22 bolt with a 1.5 thread pitch... It's packed in the right box, but I know that's no guarantee it's actually the right part....

    Tap? Or chase?

    Never having done either, since the first threads are 'toast,' how does one guarantee that the tap/chase will 'lineup' with the existing threads..?

    Thanks again for all the advice!
     
  25. mike996

    mike996 F1 Veteran

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    #25 mike996, Jul 30, 2022
    Last edited: Jul 30, 2022
    Either a chase or a tap will work for cleaning up threads. As far as buying a set, I like taps because you can chase OR cut a thread with them. But for a one time use like this will be, I'd buy whichever one is cheaper. The design of a tap/chase having a taper tends to align it "automatically." There is, of course, no guarantee that will happen but with some care it shouldn't be a problem. Put some grease - whatever grease you have around is fine (so is Vaseline if you don't have any grease) - on the threads of the tap/chase.

    There will probably be some resistance as the full-size threads of the tap/chase encounters the area where the buggered threads meet the good threads. But it shouldn't be particularly difficult to turn the tool past that point and you should feel the resistance reduce as the chase/tap is turned further in.

    Admittedly, there is some 'feel' involved where previous experience doing this is useful, especially in aluminum. But with some care, and NOT being in hurry you should be able to make the thread repair without difficulty.
     
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