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Thread: measuring fork oil

  1. #1
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    measuring fork oil

    I read somewhere that you can measure the amount of front fork oil by removing the top cap and inserting a welding rod then measuring the length of the rod that is covered in oil. Does anyone know the correct depth this should be on a 1980 R100?
    Also, though I changed the oil, the front forks "drop out" when going over a curb or hitting hole. If is "get on it" from a stop I can make the forks "clunk" in first and second gear. I know there is something wrong but not what is wrong. Any ideas?

  2. #2
    Registered User lmo1131's Avatar
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    Time for a rebuild I'd say. Rather than go to the trouble of "measuring" the fork oil why not just replace it. If your forks are "clunking" dropping off a curb, I'd be willing to bet a buck that there is not oil in them... either that or the viscosity of the oil that is in the forks is too "light".

    These will help get you up to speed.

    -> http://w6rec.com/duane/bmw/forkseal/
    -> http://bmwmotorcycletech.info/frontforks.htm
    -> http://bmwmotorcycletech.info/front-...ls-amounts.htm
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

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    Administrator 20774's Avatar
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    As for oil fill amounts, Haynes gives the following:

    - /5, /6, /7 1977 -- 437mm max from top surface of fork top plug to top of oil

    - /5, /6, /7 to 1980 -- 50mm above the damper piston

    I'm a bit confused with these two statements. Are they one in the same for the /5, /6, and early /7s? So, for 1980, how do you really know where the top of the damper piston is?

    I'd just drain and refill with the right amount. If you're trying to determine if you have the right amount, not sure what to say. Again, a drain/refill will take care of that.
    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!

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    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    Just to add to the confusion, is that measurement with the forks extended or collapsed? Sounds like extended for the older bikes. Also notice that the measurement is specified as Maximum. So that implies that that is the furthest distance from the top of the fork tube.

    Now, when I rebuild damper-rod forks, "the book" often gives volume amounts, and level from the top of the tube. Mostly that distance is inferred as with the fork leg collapsed. So, in my /6's forks, using progressive springs, totally rebuilt and dry, I collapsed the fork leg, added sufficient oil until the level was 5 inches from the top after I had stroked the fork leg numerous times to ensure the oil had worked its way to the slider. Then I extended the fork leg and installed it into the triple clamp, installed the spring, spacer and fork cap. As you raise the oil level, you have less air space in the fork leg, which changes the response of the fork, as the air volume acts as a spring.
    F.O.G.Rider, Rounder #6,
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    Administrator 20774's Avatar
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    The numbers I provided and to what Lew referenced is for forks fully extended.
    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!

  6. #6
    Registered User kwb210's Avatar
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    Just the oil?

    You state that you just changed the oil...did you check the bottom bumpers? 31 42 1 231 314 this part number is the Rubber Bumper Bottom Thread Plug. usually we find this piece is mush, it is important in the operation of the fork. It needs to be replaced most of the time if the fork oil has not been serviced in a timely manner. Top bumpers? 31 42 2 000 384 Rubber Bumper Top thread ring. I just finished a fork service on a 1977 R100/7 that I picked up last spring. The Rubber Bumper Bottom thread Plug (that's a lot to say) was all mush on one side and the other side it did not seem to even be there! What was there was a bunch of little pieces of the top thread ring. The top ring had broken into many pieces and blocked the holes in the rod that is referred to as the "pipe". Dash off to the point...rather than just replace the fluid, un-screw the bottom fork leg screw plug, observe what or what does not come out, maybe pull off the fork leg, clean everything up. I squirt some carb cleaner in from the top. New Rubber Bumper Bottom Thread Plug, about $9.50 each, and a new drain gasket, $.50 each, and a new copper leg gasket, $2.10 each, and 8-9.5 oz (435cc to 480cc) of 7.5w fork oil, $8-10 a quart, thats 32oz of juice. Pretty straight forward service, be sure and follow all the torque specs!!!!! This service will be good for two years of riding in theory. Certainly not less. Made all the difference in this little girl. If you have additional questions on the overall service, this is the place to ask 'em!
    Best regards,
    kurt

    Quote Originally Posted by lmc3881 View Post
    I read somewhere that you can measure the amount of front fork oil by removing the top cap and inserting a welding rod then measuring the length of the rod that is covered in oil. Does anyone know the correct depth this should be on a 1980 R100?
    Also, though I changed the oil, the front forks "drop out" when going over a curb or hitting hole. If is "get on it" from a stop I can make the forks "clunk" in first and second gear. I know there is something wrong but not what is wrong. Any ideas?
    1977 R100/7 1971.1972.1972.1973 R75/5
    1974 R90/6 multiple boxes
    Airhead Revival
    "Objects in the mirror appear to be losing" unk

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