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When is valve lapping not enough?

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  • #1

    When is valve lapping not enough?

    So, (if I understand it correctly) Valve lapping is when you "polish" the inside of the valve cylinder (is this the valve seat?) to fix minor wear/damage. So, I was removing the valve seals inside my '80 xs11's valve cylinder, and my tool broke while I was pulling, resulting in me jerking my hand and scoring the inside wall. F**K! damn murphy's law...
    So, am I totally screwed by needing to buy a replacement head, or can I "polish" or "lap" or whatever, the damage out? If I lap it out a bit but it is more than is technically fixable, what will happen if I just say "screw it" and leave it as it is? I am learning about engine mechanics, but am not yet familiar enough to know the consequences of leaving the damage there and hoping it doesn't bite me later

    Thx for any input,
    Scott
    Tags: None
  • #2
    That thing must SEAL. Otherwise you'll get a triple.... no compression etc....
    You can get your valve seat re-cut and repeat the excercise.
    There are tools for doing it, but any shop that can fix engine heads should be able to do it for a few bucks or a beer.
    They can tell you more bout your problem and what can be done.
    Don't forget to adjust your valve clearancies after you fix everything.

    LP
    If it doesn't have an engine, it's not a sport, it's only a game.
    (stole that one from I-dont-know-who)

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    • #3
      Re: When is valve lapping not enough?

      Originally posted by dweomer21
      So, (if I understand it correctly) Valve lapping is when you "polish" the inside of the valve cylinder (is this the valve seat?) to fix minor wear/damage. So, I was removing the valve seals inside my '80 xs11's valve cylinder, and my tool broke while I was pulling, resulting in me jerking my hand and scoring the inside wall.
      You're referring to the cavity on top of the head that the valve follower or bucket rides in? I'm sure the factory recommended cure would be to replace the head.

      I'm not an expert, but I think I would be inclined to just polish out any burrs or rough edges with fine emery cloth and put it back together. There's no compression or other pressure exerted at that point, so can't see a problem with it.
      Brian
      1978E Midlife Crisis - A work in progress
      1984 Kawasaki 550 Ltd - Gone, but not forgotten

      A married man should forget his mistakes. There's no use in two people
      remembering the same thing!

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      • #4
        Valve lapping is when you put an abrasive compoud on the face of the valve and 'lap' or turn it against the valve seat. The face of the valve is on the underside edge of the large round end of the valve, and the seat is the mating surface in the combustion chamber of the head. Not where your gouge sounds like it is.
        Brian
        1978E Midlife Crisis - A work in progress
        1984 Kawasaki 550 Ltd - Gone, but not forgotten

        A married man should forget his mistakes. There's no use in two people
        remembering the same thing!

        Comment

        • #5
          I agree with Brian,

          The large cavity is the valve lifter chamber, the lifter merely sits and slides up and down inside of that chamber, it's pressure is exerted but spread out all around the diameter of the chamber, so with a little scratch, just polish/buff it smooth with emory cloth, and you should be good to go. The valve seal below it will keep the oil where it needs to be. It flows all around the lifter while the cams are pushing down on it.

          What Brian said about lapping is of course also correct. The sealing/mating surfaces between the bottom/underside of the valve head and the seat which is in the engine head need to be very smooth to make a proper complete seal for proper compression. Over time, carbon and such can build up between the surfaces and prevent them from making a thorough contact. Lapping the surfaces by using the lapping/abrasive compound allows you to remove small buildups and imperfections between those two contact surfaces so that the valves will make a tight seal and you'll have good compression!
          HTH.
          T.C.
          T. C. Gresham
          81SH "Godzilla" . . .1179cc super-rat.
          79SF "The Teacher" . . .basket case!
          History shows again and again,
          How nature points out the folly of men!

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          • #6
            Thanks for the info guys. (I now see that lapping wasn't what I thought it was). As for the small scratch on the inside of the valve lifter chamber, you have made my day by indicating that I don't necessarily have to replace the head!! I will polish it out and go from there!
            Thx again,
            Scott

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            • #7
              Re: When is valve lapping not enough?

              If it is the lifter bucket cylinder, just lightly sand it with fine emerory and polish it. It doesn't have to be perfect, but shouldn't impede free motion. Been there, done that. I scratched mine, long ago, with a valve removal tool that was not the proper one.

              Originally posted by dweomer21

              Thx for any input,
              Scott
              Skids (Sid Hansen)

              Down to one 1978 E. Stock air box with K&N filter, 81H pipes and carbs, 8500 feet elevation.

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              • #8
                ...speaking of which, how does one go about removing the valve guides? I 'm sure there is a tool meant to do this, but I am not finding one on denniskirk.com or bikebandit.com. My parts fiche shows 8 o-rings (which I also have replacements for in my gasket set) that go with the intake & outtake valve guides, but nowhere does it say how these are removed
                scott

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                • #9
                  If you do not suspect the valve guide are bad or leaking, I wouldn't remove them. However, I removed mine by heating the head up in the oven to 400 degrees for and hour and half or so and used a round punch that I had ground down to be flat on the end. If you use something like I did, be sure the punch has no rough edges or you could scrap up the holes for the guides. Anyway, once the head is good and hot, the valve guide should drive out fairly easy. To install new guides, freeze the guides for several days in a deep freezer, reheat the head, 400 degree, and drive the cold guides back in. I used a 3/8 " copper tube to drive them back in.
                  79 XS1100 f (BIGDOG)
                  80 XS650 Special
                  85 KAW 454 LTD
                  Dirty Dan

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