1985 VF1000R Compression test

Discussion in 'Mechanics Garage' started by droopydawg, Jan 21, 2015.

  1. droopydawg

    droopydawg New Member

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    I can not find detailed instructions on how to perform a compression test on this particular bike, 1985. I am assuming, spark plug removed, gauge inserted, throttle open all the way and hit the starter?
    If this is correct, I have a question.
    The carbs are not currently installed. Do I need to install them, and hook up the cables to do this? Wouldnt performing the comp test without them be virtually the same as "throttle wide open"?
    Thanks!
    -Drew
     
  2. squirrelman

    squirrelman Member

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    You're right, carbs are not needed for a comp test. More important to see even #s on all 4 than look for any specific # ................above a minimally-acceptable 110-120psi on a cold engine. :eagerness:
     
  3. droopydawg

    droopydawg New Member

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    Excellent. Thank you for confirming my idea. Had thought that perhaps the venturi affect of the carbs may have been necessary for an accurate reading, but doubtful it would make that much of a difference.
    -Drew
     
  4. GreyVF750F

    GreyVF750F Member

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    For a proper compression test the motor should be up to temp. You may see some bogus numbers when cold. If not then you have real good ring seal.
     
  5. droopydawg

    droopydawg New Member

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    Trying to determine if #2 is drastically off from the other three. I bought this project from a guy who also bought it as a project but never started it. He was told by his PO that #2 may have a bent or cracked con rod. I figure if the Comp number is that different than the others, then I will know whether to open up the lower end. otherwise, I was going to do new rings and freshen up the top end anyway.
    Was also going to see if the piston goes up and down with the rest, as I turn over the engine by hand.
    Thx
     
  6. vfrcapn

    vfrcapn Member

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    Up and down would be good, side to side not as much.

    [​IMG]
     
  7. squirrelman

    squirrelman Member

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    Yes, but........

    Sometimes you're testing a non-running engine and need to verify even compression before potential purchase in a cold, dark garage, and it hasn't been runin in 2 years.
     
  8. droopydawg

    droopydawg New Member

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    All pistons go up and down when turning over by hand. they top out and bottom out at the same place. Looked at surface of all pistons look fine, so not holed.
    Next, I will do comp test on cold engine. if nothing is apparent, will top off all fluids, replace a couple of seals in coolant plumbing, new plugs and start it.
    PO said there was a clear knocking. When removing the original plugs, one was bent where it "snaps" onto the spark plug wire, which happened to be the cyl that he said was knocking around a bit. That plug not sparking? C'mon, it cant be as easy as that. No spark and just detonates when the amount of air/fuel in there is so great, compression causes the "knock" detonation.
    That would be a nice fix.
     
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