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Thread: cam timing

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  1. #1
    jimmy armour
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    cam timing

    hi guys I guess its my turn to ask for input,I have a 1977 r100s and am about to replace the timing chain,the third one in 340,000kms,and am thinking of installing an offset woodruff key to advance the valve timing as per the 1978 on bikes ,has anyone done this and what was the result?thanks in advance Jimmy

  2. #2
    Administrator 20774's Avatar
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    Hmmm...why would you want to do that? The '77 models have some of the highest power of the Airheads. The began the detuning process with the '78 models....this was aimed more at satisfying EPA requirements than anything else. I've heard it started with the January 1978 bikes but it could be all of them.
    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!

  3. #3
    Rally Rat
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    There is a increase in torque with the advance in valve timing. I have altered valve timing with sport cams and aftermarket performance cams and have had no problems with key failure. I add a bit of Loctite RC609 when doing this. The latest offset key from San Jose BMW is a nice, if expensive piece.

  4. #4
    jimmy armour
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    cam timing

    hi guys thanks for replying ,I was aware of the differences in cams and why, way back when my bike was sporty and so was I, I too had made a lot of mods sports cam etc,but over the years have detuned ,std cam and lowered compression,what I was wondering was how my bike would run,with the san jose off set key ,much more torque or some ? my exaust has always been black never grey like my riding buddies,off coarse i have rebuilt the carbs many times over the years,and changed float needles ,twin bing float kit,needle jets, mainjets and needle positons ,but exaust remained slightly black sootie (rich)I put it down to the dirty cam and pistons,since then I have had her rebored and new 1978 on type pistons installed, so did anyone note an improvement in tractability ? thanks again Jimmy

  5. #5
    Sir Darby Darryl Cainey's Avatar
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    How are you taking your plug readings Jimmy?

    Back in the day when I was setting up my racebike we ran it very hard and shut it off, then checked the plugs.
    If you are just running easy on idle you won't get the plug reading you want.

    Ride it like you stole it!
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    1977 R100RS, (Retired) 1993 R100GS (just getting started)

  6. #6
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    Opinion, if engine runs black at tailpipe, might be burning oil? Way back in old clymer book, the only mention of using offset key on cam is to degree a new cam when installed, if needed. Don't really know why airhead would need, or could use more advance in timing than is available? Depending on year of manufacture, which is around 27 degrees. With the low octanes available today as opposed to what was available, would advanced timing increase ping?

    Much has been posted about cams, as stated before, I run 336 in 90S, don't find it racy or peaky, just breathes real good, timed at TDC with dual ignition, pulls real good from 4K on up. Always thought airheads love to spin, hate to putt putt.

  7. #7
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    Quote Originally Posted by 20774 View Post
    Hmmm...why would you want to do that? The '77 models have some of the highest power of the Airheads. The began the detuning process with the '78 models....this was aimed more at satisfying EPA requirements than anything else. I've heard it started with the January 1978 bikes but it could be all of them.
    I am confused!!! I always thought that BMW upped the horses of the 1000cc in 1978 from 65 or so to 70. What do I have wrong??

  8. #8
    Administrator 20774's Avatar
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    Quote Originally Posted by EMSimon View Post
    I am confused!!! I always thought that BMW upped the horses of the 1000cc in 1978 from 65 or so to 70. What do I have wrong??
    My '78 R100/7 is shown as only 60Hp but the same year R100RS or RT was 70 Hp. That's probably in the difference in compression ratio 9:0 to 9.5.

    I don't imagine the EPA requirements they had to comply with did any good to total performance. Hp is only one measure of performance.

    I've always had it in my mind that the pinnacle of the total Airhead package (in terms of engine performance) was the 1977 bikes.
    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!

  9. #9
    Registered User lkchris's Avatar
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    Quote Originally Posted by 20774 View Post
    My '78 R100/7 is shown as only 60Hp but the same year R100RS or RT was 70 Hp. That's probably in the difference in compression ratio 9:0 to 9.5.
    And in the larger valves and 40 mm carbs.
    Kent Christensen
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    '12 R1200RT, '02 R1100S, '84 R80G/S

  10. #10
    Sir Darby Darryl Cainey's Avatar
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    The 70 HP was from the 77RS with 40mm exhaust, yes?
    Ambassador BMW MOA Ontario Canada
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    1977 R100RS, (Retired) 1993 R100GS (just getting started)

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