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    #1

    Riddle me this

    Ok this is really strange, last weekend I put the head back on my 83 GS1100GK due to having to have a cam cap bolt that broke off removed. When I finished getting everything except the airbox back on the bike, I decided to do a compression check before actually starting it up. Turns out #4 cylinder has no compression, so I got upset and just walked away from it. Well this evening I went out to measure my exahust headers to make sure that Detman's will work for my bike. While I'm in the garage, I decide to just double check #4's compression. Now #4 had almost 90lbs compression. Why would it not have any last Sunday and now have 90lbs? I haven't tried to actually start it yet, it was too hot to stay in the garage for more then a few minutes this evening, (Detman didn't get the measurements, but will first thing tomorrow morning if you read this). I'm going to put the air box on tomorrow morning and see if it will start. If anyone has any ideas on this I sure would like to hear them. Thanks
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    #2
    You did it wrong the first time. 8)

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      #3
      Swanny when I did it Sunday I could stick my middle finger in the spark plug hole and couldn't feel any pressure at all, today I stuck my finger over it and it blew it off, so that was when I put the pressure gauge on it. I can't figure it out. Not that I'm complaining really, because I sure don't want to have to pull the head again, I want to get some riding in this summer not just work on the &*(# thing.

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        #4
        Originally posted by dgeorge
        Swanny when I did it Sunday I could stick my middle finger in the spark plug hole and couldn't feel any pressure at all, today I stuck my finger over it and it blew it off, so that was when I put the pressure gauge on it. I can't figure it out. Not that I'm complaining really, because I sure don't want to have to pull the head again, I want to get some riding in this summer not just work on the &*(# thing.
        I think I read in another thread here that you need to have the throttle open. (Or maybe I misunderstood. I'm still learning this stuff.)

        Dave

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          #5
          Dave, that is true to get the correct compression readings you need to hold the throttle wide open, but even with it closed you will still have some compression, and Sunday when I checked it there was none what so ever. I've been testing compression on cars for almost 40 yrs and never seen one not have any one day and then have almost 90#'s a week later with nothing having been done to it. It just has me baffeled, I don't know what to think.

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            #6
            A piece of debris may have been stuck on a valve seat.

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              #7
              strange

              Its more than likely what don says but it may be that you have a tight valve and the first time it may have been cold and the valve not closing and then you checked it on a day that you said was to hot to stay in the garage, and the heat gave you the difference to allow the valve to close, just a few degrees can make a differece in the valve clearence, I checked mine the other night I had 2 intakes that where tight .0012, when I rechecked them the next afternoon the where .0025 that outside temp was 83 degrees verses 50 degrees the previous night

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