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Valve lapping gone wrong (I think)

Discussion in 'The Garage' started by webbie, Aug 21, 2016.

  1. webbie

    webbie XS650 Member

    I'm about halfway through my top-end rebuild, and I decided to lap my valves while they were out. I'm regretting that decision now.

    They weren't too bad, but there was a small amount of visible pitting and roughness.

    Now, I've got these grooved rings around the valve and seat, which is - if I understand correctly - THE thing to avoid when lapping valves.

    IMG_20160821_133034.jpg IMG_20160821_133112.jpg
    I'm not sure how I did such a poor job of it....

    I've never done valves before, granted. But before anybody bites my head off - yes, I read up on how to do it. Thoroughly. I read the cautionary tales and watched the videos.

    I used a suction-cup type lapping stick and a combined pack of the course/fine lapping compound. I was conservative with my application of the compound. I started with the course, and once it stopped making noise, I wiped it off and transitioned to the fine grit. I lifted the valve, rotated them, and smacked it back into the seat to spread the compound whenever the sound started to change (or sometimes more frequently)....

    I cannot, for the life of me, figure out where I went astray. Anybody? And how buggered are my valve and seat?
  2. 5twins

    5twins XS650 Guru Top Contributor

    A small amount of grooving usually does happen but that does look excessive. Your head looks filthy, still all crusted up with carbon. My best guess is bits of that carbon were breaking off and getting in between the valve and seat as you lapped, and that caused the more pronounced grooving.

    Engine work can be compared to a medical operation on a human. Everything involved needs to be super clean for best results. Some of the rebuilds I see documented around here are just terrible when it comes to the cleaning part. Their "clean" parts look like my dirty ones, lol. When they post back later after the "rebuild" complaining of engine smoking and/or oil leaks, it doesn't surprise me in the least.
  3. webbie

    webbie XS650 Member

    Yeah, that's a fair point on the cleanliness of the head. I'll renew my effort to clean up the carbon deposits before attempting any more valve work. I knew they weren't very clean, but I hadn't thought it was imperative to clean off carbon that wasn't actually encroaching on the valve seat. I need to get my hands on some piston kleen now.
  4. 5twins

    5twins XS650 Guru Top Contributor

    Plain old paint stripper will soften and practically melt the carbon away. It may take a couple applications. Follow that up with a little chrome cleaner and you should end up with something like this. Now you're ready for valve lapping .....

  5. Jack

    Jack XS650 Junkie Top Contributor

    Take the head to a reputable auto machine shop to have the seats and valve faces recut professionally and throw that suction cup in the trash where it belongs.
  6. webbie

    webbie XS650 Member

    I probably will have to take this head to a shop, now that I've scored the valve seats with my first lapping attempt, but I was doing my best to keep unnecessary costs to a minimum. I know that lapping by hand is something of a contentious topic, but it certainly has its merits, no?
  7. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

  8. webbie

    webbie XS650 Member

    Yeah, I caught that video before I lapped. I imitated the technique as closely as possible, but no dice. My theory now, beside the one proposed by 5twins, is that I didn't mix a sufficient amount of oil into the course compound. It came as a very thick paste, which I tried first without thinning it. The overly-thick compound may have not spread very evenly around when tapping the valve into the seat...
  9. Bigfeet

    Bigfeet to many projects

    Now there's one I never thought of. Thanks 5twins!
  10. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    The spreading is something that you need to do, can't put a couple of dabs on and expect it to spread evenly itself. Culprit would be as 5twins suggested, contamination getting into the past on the job. Clean all surfaces and surrounding areas prier to any work and have a clean space to work on
  11. webbie

    webbie XS650 Member

    I didn't mean that I just globbed on some compound and went at it. I spread a light even layer around the valve with my finger before beginning to lap. I'm referring to the re-distribution of lapping compound that occurs during the tap-tap-tapping of the valve into the seat. I think that may have been hindered by an overly-thick compound. I doused the head in a liberal coating of aircraft stripper and went at the coke deposits with a plastic blade to pretty good effect last night. Thanks for that tip 5twins! Does even better than simple green.

    I'm taking the head to a machine shop this afternoon for a consultation. If the prices ain't outrageous, I may have him do a full valve job. IIRC, ToomanyXS1bs posted that the hardened coating is only 0.005" thick, so I'll see if my machinist can work with that.
  12. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    The stellite coating is actually thicker. We just worked under shop and industry advisement to avoid grinding more than 0.005", to avoid thinning it too much.


    Here's a manual excerpt with valve data:

  13. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Strange, double post...
    Last edited: Aug 23, 2016
  14. webbie

    webbie XS650 Member

    Ahh, many thanks toomanyxs1bs.

    I can't be sure that they haven't been ground before, but all indications would suggest I'm the first to tear into the top end, so I suspect that they have not.
  15. webbie

    webbie XS650 Member

    Okay, just dropped my cylinders and head off at the machine shop. Running me $110 for the 1mm oversize bore and $30 for valve + seat cleanup. The machinist was familiar with stellite facing, and assured me they wouldn't cut through it.

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