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Thread: 1981 R80G/S final drive fluid qty and stripped fluid level/inspection plug

  1. #1
    Day Dreaming ... happy wanderer's Avatar
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    1981 R80G/S final drive fluid qty and stripped fluid level/inspection plug

    As I just got done with a leak repair on my 81 G/S final drive I ran into some issues.

    Questions:

    1) What is the correct amount of 80/90 gear oil to put in? The factory manual states .35 ltr or 350 milliliters however I found that the oil started coming out of the fluid level/inspection hole at the rear when I had about 275 to 300 mL in there.

    2) The PO of this bike was really ham fisted and I have discovered the final drive fluid level plug/inspection plug at the rear of the drive is stripped. This is the 3rd stripped maintenance related threads I've found on the bike. What's best here? Helicoil or time sert? Do I have to split the drive open to fix this properly so as not to end up with filings inside or can it be done from the outside.

    An Airhead buddy tells me I should never use that level plug (because they strip so easily and so many of them are already stripped).

    He also said I should just put 320 mL of oil in there after draining even though the spec is 350mL.


    I'm all ears on both subjects. What say ye?
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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    Administrator 20774's Avatar
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    Haynes says 350ml and that the plug at the 12 o'clock position is the fill plug for '81-on. I think people just drain and refill with the proper amount...maybe bias it a little lower since a small amount stays inside?
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
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    stripped threads in final drive

    I've used both as either will work. You can do the fix without taking the final drive apart. Get the shortest helicoial or time serts they have. Follow instructions that come in either kit. One problem you will deal with could be the the short lengh of the plug housing. The kit will probably have 1 tap with a pointed or tapered end. If this is the case you will need a bottom tap. Use the kit tap first and if the tap bottems out after cutting a couple of threads, you will then use the bottom tap to the cut the treads deeper into the hole. If you can't find a bottom tap, you can buy a standard tap and grind the pointed/taper end down where the threads will then go full width to the bottom of the bottom of hole. Before running a drill bit or tap down in the hole check ahd see how deep you go till you hit an obstruction. Stick a scribe/ hanger down in the hole and get a idea of the lengh. If there is an obstruction there all drilling and tapping needs to stop at that point, don't force it. When using a drill or tap apply gease on the end, if your very carefull most of the chips will collect on the drill bit or tap. Another option is use a strong shop vac and have a buddy use it as you drill and tap. Good luck with your project.

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    Day Dreaming ... happy wanderer's Avatar
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    Thanks Kurt and barryg. I'm surprised that there is a fill hole at the top of the final drive and a fill/inspection hole at the rear. Not really sure just what you could inspect from this rather small opening and the threads are so fine that finding it stripped was really not surprising. I would imagine this is a common problem. Hopefully easy enough to fix. I don't have any helicoil or timesert tools laying about so will have to look into that.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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    Benchwrenching PGlaves's Avatar
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    Quote Originally Posted by happy wanderer View Post
    Thanks Kurt and barryg. I'm surprised that there is a fill hole at the top of the final drive and a fill/inspection hole at the rear. Not really sure just what you could inspect from this rather small opening and the threads are so fine that finding it stripped was really not surprising. I would imagine this is a common problem. Hopefully easy enough to fix. I don't have any helicoil or timesert tools laying about so will have to look into that.
    I might be wrong - I have been before and assume I will promptly be corrected if so - but I think the original instructions were to add oil at the top opening until it ran out the "inspection" hole. This in lieu of the older models where you fill to the bottom of the threads of the fill plug down lower in the housing.
    Paul Glaves - "Big Bend", Texas U.S.A
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    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by PGlaves View Post
    I might be wrong - I have been before and assume I will promptly be corrected if so - but I think the original instructions were to add oil at the top opening until it ran out the "inspection" hole. This in lieu of the older models where you fill to the bottom of the threads of the fill plug down lower in the housing.
    No I think you are correct Paul. I was doing exactly that; filling it from the top till it ran out the "fill"/inspection hole. I was advised by another airhead owner the common advice nowadays is to fill with a known quantity of gear oil and not use the rear plug at all because it is so easy to strip the fine threads they used there. He was right. The PO must have over tightened it and now it's my problem.

    My plan was to do this once, carefully measure the amount of oil used till it ran out the rear hole and never open it again.
    Yeah right!

    Oh, and it turns out somewhere around 330mL to 350mL is probably about right. Just like it says in the manual. Sometimes I just over think things....
    Last edited by happy wanderer; 09-28-2013 at 07:23 PM. Reason: typo
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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    Registered User helmut_head's Avatar
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    You may want to check and see if the threads are stripped all the way in. I found two-three threads stripped on mine. I went in deeper by adjusting the nut on the bolt, slowly worked it in and out (oh yeeess!) and she held fine. I'll never remove it again.
    Helmut always wears a Helmet.

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    Registered User jimbc's Avatar
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    stripped thread

    Try looking at Snowbums site. I think he prefers helicoils.

    Try this google search. site:bmwmotorcycletech.info helicoil

    Thanks to Kurt, it's my favorite search method.
    1985 R80 Original owner

  9. #9
    Registered User toooldtocare's Avatar
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    On the idea of adding oil until it runs out the small plug (level plug) I had a bad experience on my then almost new 86 R80RT. I removed the small plug and poured the oil in. It did not take much before oil ran out the small hole so I assumed all was well and it was at the correct amount. But, I looked at my container and realized that I had hardly put any in, maybe 100cc's. I drained the oil again and found that I was right, it was way under the correct level.

    Seems there is not much room between the ring gear and the case, so oil can run down the ring gear and some of it runs out the small hole. As others said, from then on I just measure the correct amount and pour it in. I do not know what would have happened if I rode the bike with only about 100cc's of oil in it, but I do not think it would have liked it. That small plug never came out again as long as I owned the bike.

    Wayne

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    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by toooldtocare View Post
    On the idea of adding oil until it runs out the small plug (level plug) I had a bad experience on my then almost new 86 R80RT. I removed the small plug and poured the oil in. It did not take much before oil ran out the small hole so I assumed all was well and it was at the correct amount. But, I looked at my container and realized that I had hardly put any in, maybe 100cc's. I drained the oil again and found that I was right, it was way under the correct level.

    Seems there is not much room between the ring gear and the case, so oil can run down the ring gear and some of it runs out the small hole. As others said, from then on I just measure the correct amount and pour it in. I do not know what would have happened if I rode the bike with only about 100cc's of oil in it, but I do not think it would have liked it. That small plug never came out again as long as I owned the bike.

    Wayne
    It's an interesting dilemma. I've just been reading about final drives on Duane Asherman's site and the common issue of drive shaft gear oil migrating into the final drive causing an over fill condition. He also talks about the drain holes getting plugged so this over fill condition then leads to higher pressure in the final drive and you've got gear oil on the brakes again. Easiest way to check for overfill in the fill/inspection plug or I guess you can drain it into a measuring container and see how much was in there. He also says never to fill past the bottom threads of the rear fill/inspection hole. I guess draining and refilling with just under 350 mL is probably the easiest way to deal with this.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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