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Thread: Loud clatter/ chatter when warmed up 1975 R90/6

  1. #1

    Loud clatter/ chatter when warmed up 1975 R90/6

    Just purchased a 1975 R90/6 two weeks ago. Did not go for more than a mile test ride because of in-op front brake. All seemed very well, except for front brake. After I rebuilt the master cylinder, went for first real ride. After about four miles when I came to a stop, noticed loud clatter / chatter from down below. Rode it home and made some checks. When engine cool, all purrs like a kitten. Very smooth, engine, transmission, clutch, seem to all be perfect. When first take off only sound is the exhaust. After four to eight miles is when the noises begin. When stopping at sign or traffic light at below 1500 rpm clatter / chatter begins, and it is loud. Doesn't matter if in neutral, or in gear, clutch in or out, noise is there all the time. At around 1500 rpm in neutral, or in gear taking off from dead stop, loud clatter/ chatter is there till 1500 rpm then all is quiet. Have tried research and many over the years have reported what sounds like the same noise, just varying hows and whens. Problem is no more posts were added giving what the problem or fix was. Have never heard this sound before on any other motorcycle with cam chain, transmission, crank issues. Since this is my first dry clutch motorcycle which happens to match the first time I have ever heard this kind of sound before, my guess is clutch issue of some type. Though, as at any time, I could be wrong. I have checked timing, set valves, sync'ed carbs, and adjusted the clutch, handlebar, and below correctly. The only thing which seemed to effect it was carb sync. Before carb sync, once engine was warmed up noise would be there all the time, from idle all the way to 5000 rpm while traveling down the road. Once synced, problem improved to 1500 rpm and below?? Have tried to isolate noise with stethoscope made for such things and all I hear are pleasing whirring, spinning sounds. But at the same time still hear the loud chatter/ clatter from the out side. I have been riding it anyway, it's so darn fun to ride. But I need to know whats going on and why plus how to fix it.

    Thanks

    Bikertucker

  2. #2
    Liaison 20774's Avatar
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    Since it's your first BMW, and an Airhead, to some degree the saying "they all do that" might come to mind. They do rattle a bit at idle and it tends to clear up when the clutch is pulled which then isolates some of the shafts in the transmission. But it shouldn't be that noticeable at speed.

    First thing I thought was valve clearances. It wouldn't be the first time for a new BMW owner to get this wrong. But just to be sure, the valves are set at 0.15mm intake and 0.20mm exhaust. Each side is set at top dead center in the rotation on the COMPRESSION stroke. It's important to get the cylinder being adjusted at TDC just as the cylinder is rising on the compression stroke. Watch the valve action to confirm.

    Another thing that you should probably confirm is to torque the heads. This is done on a cold engine. Use a criss-cross pattern and shoot for 25 ft-lbs for each bolt. This is done with the given cylinder at TDC on the compression stroke.

    While doing the head bolt torque, you should ensure that the up-down motion of the rocker arms is minimized...at TDC on the compression stroke, you should be able to move the rocker arm up and down and only see slight oil film movement where the rocker meets the pillow block. If you see more than that, check section 10-11 on this page:

    https://w6rec.com/bmw-motorcycle-val...ent-procedure/
    Kurt -- Forum Liaison ---> 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!

  3. #3
    Thanks for the reply. Valves were set at correct tolerances. But need to ask a question. Have set valves on engines from flat head six's, farm tractors, engine generators, and sport bikes. Have never ever heard a valve make any sound that comes close to this sound. Not doubting your advice, but the other posts I've read with others reporting the same thing, valve clearance is the first item in the check list. This sound is not a typical metallic clatter, plus it goes away at 1500 rpm on up. Have yet to work on an engine that valve clatter goes away as rpm increases. With that said ,I am brand new with this engine, so will check as suggested. Did check torque on all six bolts/nuts under valve cover. Did not know about nor check up down motion of rocker arms. Will make this check as time allows.

    Thank You

  4. #4
    I suspect you are hearing gear rattle in the transmission, originally described in 1975 by famed Airhead Oak Okleshen thus:

    "The noise is the result of an unloaded transmission and the backlash in the mating parts clattering slightly due to variances in engine speeds when at idle. The engine, though we think of it as running at a constant speed, varies in a miniscule amount when it is unloaded and at low speeds near idle. This happens between the power pulsations from the pistons. The flywheel helps to prevent the uneveness but does not cure the problem entirely for it would take a much larger and heavier flywheel than necessary to make the machine run properly and would detract from acceleration performance. As a result, the engine pulsates and the transmission attempts to run at a constant speed. Between pulsations the backlash in the transmission causes the components to clank lightly and cause noise.

    The noise can become more noticeable if ...unbalanced left to right. This causes engine pulsations to become more uneven and, hence, there is more noise in the transmission in neutral, clutch engaged."
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  5. #5
    When doing timing and valve checks found markings on flywheel not the ones given in owners manual. For instance not an (S) mark, rather a large (=) sign. From what I found during research it could mean a lighter aftermarket flywheel was installed. From what your saying, if it does have something to do with transmission a lighter flywheel would make it worse. Do you think a heavier gear lube in transmission be of help or hindrance.

  6. #6
    Gerard jagarra's Avatar
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    One other thing to check is the side play of the rockers on the shaft. IIRC the manual says you want a minimum of side play. Mine were noisy, especially at idle and would smooth out as RPM increased.
    1994 R1100RS-(5/93)-,1974 R90/6 built 9/73,--1964 Triumph T100--1986 Concours

  7. #7
    Liaison 20774's Avatar
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    Use the standard gear lube (80w90) in the transmission...don't try and out guess things.
    Kurt -- Forum Liaison ---> 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!

  8. #8
    Registered User kentuvman's Avatar
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    Biketucker - welcome to our forum and Airheads - they're awesome once one sorts things out . . .

    I had a R60/5 an replaced the clutch but not the diaphragm, pressure plate or compression plate - for about 500 miles, until the clutch mated with the plates, just from riding the bike, I had a pretty loud clatter when taking off - not saying this your issue but it does sound like something drive train / tranny related.

    You didn't indicate what part of the country you reside - there's a national Airhead community in most large cities and most Airheads are willing to help out - there's tech days throughout the riding season and at the MOA Rally in Des Moines this year there's an Airhead tent where folks take their bikes to help solve problems they can't figure out.

    You sound pretty bright and knowledgeable about mechanics - wouldn't be bad idea to contact an Airhead member and ask for some advice. The website for Airheads group is Airheads.org

    Good Luck!
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    K1200GT & R65LS

  9. #9
    Thanks all. Will check side play in rockers. When I changed out gear lube, replaced with 80w90. Living in Pelzer South Carolina. Will look up Airhead.org. Family visiting next few days. Will get back to it then.

  10. #10
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    [QUOTE=PGlaves;1130306]I suspect you are hearing gear rattle in the transmission, originally described in 1975 by famed Airhead Oak Okleshen thus:

    "The noise is the result of an unloaded transmission and the backlash in the mating parts clattering slightly due to variances in engine speeds when at idle. The engine, though we think of it as running at a constant speed, varies in a miniscule amount when it is unloaded and at low speeds near idle. This happens between the power pulsations from the pistons. The flywheel helps to prevent the uneveness but does not cure the problem entirely for it would take a much larger and heavier flywheel than necessary to make the machine run properly and would detract from acceleration performance. As a result, the engine pulsates and the transmission attempts to run at a constant speed. Between pulsations the backlash in the transmission causes the components to clank lightly and cause noise.

    The noise can become more noticeable if ...unbalanced left to right. This causes engine pulsations to become more uneven and, hence, there is more noise in the transmission in neutral, clutch engaged."[/QUOTE

    Oak was a great guy.

  11. #11
    Just an FYI. There are a couple of guys that are old time Airhead guys just up the street from you in Greenville SC on 291 By-Pass just north of Rt. 29. The business is called Trophy Moto and they cater to old BMW's and Triumphs. They figured out a thing or two for me once on my 1978 R100/7.

    I live just west of Easley near Liberty!
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

  12. #12
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    +1 on Trophy Moto up in Greenville. I'm just down the road from you as well in Williamston, been on my Airhead for 34 years, I don't mind sticking another ear on it if you need.
    Dave Hutton '78 R100S (mfg 7/77)

  13. #13
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    wow

    we could have an airhead tech day in the area!
    Enjoying the ride, but always on the alert for a rally.......

  14. #14
    Very good once again, thanks guys. Will take note of Trophy Moto in Greenville. Sent you a PM kinterridge.

  15. #15
    Rally Rat 1074's Avatar
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    If, as you say, the noise is still there at the same level with the clutch pulled in Then I think that that should eliminate the "usual" transmission noise.
    If the noise is louder with a warm engine, and it goes away when the revs go up, then it could be a loose timing chain that can make a lot of noise. How many miles are on the machine?
    Boxerbruce

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