Airhead rocker arm

Discussion in 'Old's Cool' started by madseklo, Aug 8, 2019.

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  1. madseklo

    madseklo n00b

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    Hello,

    I just bought an 1978 R100RS. It makes a ticking noise and smokes white from one cylinder. Today I checked valve clearance and notised that it was installed washers on the rockerarms. This is done on all 4. Does someone know why?

    Sorry for the bad picture.

    The pushrod tube is not all the way in, and it is hammered on. should i replace it?

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    #1
  2. Mista Vern

    Mista Vern Knows all - tells some.

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    Sir, you will have far better results concerning your question if you post it in the "Airheads" section, which you will find above this one.
    #2
  3. Andyvh1959

    Andyvh1959 Cheesehead Klompen Supporter

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    Could be valve recession into the heads as some late 70s airheads were known to do. Valves recessed into the heads when BMW changed the valve seats material and gas was changed to eliminate lead. The valve gets "hammered" into a tulip shape and the valve clearance is taken up. There are no washers for the rocker arms other than shims that may be there to take end end play.

    When you checked the valve clearance, was there any clearance? Were the valves tight? I'd suggest a leak down test to start with. But it may require a head rebuild with modern valve seats and new valves.
    #3
  4. bmwrench

    bmwrench Long timer

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    The "washers" you see are radial needle bearing assemblies. They were an after-sales modification BMW emulated in 1985. Don't do anything with the pushrod tube. They are difficult to install, and the factory often didn't get them all the way in.
    #4
  5. yokesman

    yokesman Long timer

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    I think the 78's were the first of the "unleaded" engines, you may want to do research regarding changes that the factory may or may not have done for that year. As the gentleman said, the airhead thread is the place to be.
    #5
  6. bmwrench

    bmwrench Long timer

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    We didn't have much trouble with valves until 1981. BMW had installed a very hard valve seat, used until 1984, that caused most of the trouble.
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  7. madseklo

    madseklo n00b

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    Valve clearance was perfekt. I have done a leakdown test, and the leak was even 6-7% on both sides.
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  8. madseklo

    madseklo n00b

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    Thank you! Do you know where I can buy new? Or can I take them off? One off the needle bearings was really loose and damaged. Maybe that is the reason for the ticking noice?
    #8
  9. Andyvh1959

    Andyvh1959 Cheesehead Klompen Supporter

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    Da frozen tundra eh? 1.5 mile west of Lambeau
    Strongly suggest you get a good repair manual. These airheads go for hundreds of thousands of miles (I personally have seen 400,000 and 500,00 miles each on one bike). But, they must be properly set up and maintained.

    If you have the heads off, what do the valves look like? Valve recession causes the valve circumference to be knife edged and formed into a cup shape. If your valves look normal where the the valve cut angles are clearly visible.

    Also research BMW valve recession on the internet to understand the issues some late 70s to the mid 80s airheads suffered after BMW changed the valve seat material and lead was removed from gas. The valve may actually look ok, but the valve seat itself get hammered deeper into the head, and valve clearances tighten up instead of getting more loose over time/miles.
    #9
  10. bmwrench

    bmwrench Long timer

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    I wouldn't delete them. I have them in stock.
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  11. madseklo

    madseklo n00b

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    Where can I buy them?
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  12. bmwrench

    bmwrench Long timer

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    #12
  13. bmwrench

    bmwrench Long timer

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    You have this backward. The seats looked great, but the valve head would deform and wear to a razor edge.
    #13
  14. Andyvh1959

    Andyvh1959 Cheesehead Klompen Supporter

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    Opps, right, the valve itself gets hot and hammered into the seat. The valve ends up with a near knife edge around the perimeter of the head.
    #14
  15. robtg

    robtg Long timer

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    I have seen them both ways. Sometime the seat, sometime the valve, or both at the same time.
    #15