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Thread: Valve gaps - '78 R100/7

  1. #1
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    Valve gaps - '78 R100/7

    I know, I know, this question has been asked many times!

    What is the current most popular valve tappet gap settings for a '78 R100/7?

    I have heard a variety of gap settings.

    The most recent: Intake, .004 & Exhaust, .008.

    I have also heard: Intake .006 and Exhaust, .008.

    Has there been any sort of consensus?

    Years ago, on my R50/2, it was recommended to be .006/.008 but I found that .008 on the exhaust was too tight and when engine got hot, it would never totally close - evidenced by hard starting. I went to .009+ and problem totally solved!

    I want to check/reset my valve and want to go with what has proven to work over the years!

  2. #2
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    Intake .006 and Exhaust, .008 is what you should use

    The hot starting problem with your /2 was more likely weak coil problem when hot which is usually easily solved by using less plug gap .020 or even as little as .015
    Highly unlikely valve was not fully closing with .008 clearance unless you had some other problem which caused engine to run much hotter than designed

  3. #3
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    Agree on the 0.15mm and 0.20mm, although 0.10mm could be OK on the intake side as it runs cooler. Snowbum mentions a "loose" 0.20mm on exhaust. I'm breaking in my /7 after a top end...I've been running 0.25mm on exhaust per recommendations from Ted Porter. I'll be dropping that to something between 0.20 and 0.25 on the next valve check.
    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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    As clearance decreases over time, valves should be adjusted at the loose end of the tolerance.

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    Quote Originally Posted by 44006 View Post
    Intake .006 and Exhaust, .008 is what you should use

    The hot starting problem with your /2 was more likely weak coil problem when hot which is usually easily solved by using less plug gap .020 or even as little as .015
    Highly unlikely valve was not fully closing with .008 clearance unless you had some other problem which caused engine to run much hotter than designed
    Do you really mean that my re-adjusting the valves out (particularly the exhaust) that my coils actually improved?

    I had the same coils and plug gaps after the valve adjustment and the warm/hot starting problem was solved!

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    I think what he was suggesting is that the reduce plug gap requires less energy to jump and that might allow a weak coil to still work. Certainly having the right valve clearance can help starting.

    But the /2s have a known issue that can crop up over time. The magneto coil has many windings and over time, these windings begin to break down. It's often visible when the coil is squeezed...they become soft. Instead of having one very long winding which produces a strong spark, there are many small windings which result in a weak spark. This is made worse when the coil heats up. Sometimes the cure is to wait for everything to cool down. Another solution is to use a solid state coil that is now available...form/fit/function replacement. I had the same problem with hot starts on my R69S. I tried a new coil..didn't help. Turns out my problem was my hot-start technique. I had to be different the cold-start situation. I couldn't figure it out. It took a riding buddy to try it...I now use the "Jay" method for starting the bike. Works fine...but I'm still anxious everytime I try and start the bike after a gas stop.
    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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    Only loosening up the gap on the exhaust solved my hard starting problem.

    Though I think that there are standards, I suspect that the very same part, made of the same material my react differently to heat.

    I think that what was happening, was that the push rod, when heated, would expand (lengthen) more than other's did, hence the extra .001 - .002 solved the problem!

    The only other ignition problem I had on that bike was the condenser failed, and I had to push the bike home from about 4 miles out. Of course, I picked a route that included a lot of downhills, and got on it and coasted some of the way!

  8. #8
    Registered User lkchris's Avatar
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    It's a German bike and will surely perform better set to metric measurements.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

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    I set my valves at .006 & .008 on my 1975 R90/6
    I killed the battery the other day by leaving the ignition on. I was attempting to push start my bike for the first time in many years, Not a very big hill in front of my house. By the time I got the bike going fast enough to start I had to slow down before I could hop on. Wasn't working out as good as it did back when I was in my 50's. Maybe it was the coil?

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