Valve Lash after Top End Clean Up

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by Cpt. Ron, Aug 22, 2013.

  1. Cpt. Ron

    Cpt. Ron Advrider #128

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    I tried asking this in the Garage forum and got nothing.....

    So I'm in the process of putting my 950 back together. I took the top end and jugs off to fix a leaking base gasket. While the heads were off, I decided to clean up the valves and seats using some valve grinding compound. Upon reassembly, I double checked the valve lash was reasonable with the shims that I had in the motor before tear down. A short run up to verify that everything worked and then one more check of the valve lash. Two of the exhausts had significant increases in the lash measurement. According to my log, the last measured gap was .254mm, but now one is .406mm and .356mm.
    All of the parts in the valve train went back into their original position, nothing got mixed up.

    Now, I'm not surprised to see a change in the lash after doing the work that I did. But I figured the lash would decrease since I removed carbon as well as a little material from the valve and seat faces. Am I worrying about nothing? Can anyone explain the change?
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  2. nomad guy

    nomad guy A legal alien

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    Sounds like a trick question cause it doesn't make sense.
    Are you sure there is no human error in measuring?
    Did you try giving the engine a few more turns after those measurements?Just to make sure.
    #2
  3. Cpt. Ron

    Cpt. Ron Advrider #128

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    Yeah, it doesn't make sense, hence me posting here with my hat in hand.....

    Yeah, I'm going to double-check the measurement. But to back up what I measured, I did run the bike and there was certainly excess noise due to the large gap on the exhaust valve.

    So, what can it be?

    Measurement error? Most likely, I am human. But I find it hard to squeeze in too-tight feeler gauges.
    Took too much material off of the stem of the valve? Not likely, since I didn't touch that end.:rofl
    Added too much hard facing on the valve? Doubtful, I can't weld like that and didn't try anyway....:deal
    Some dust/debris between the valve face and seat? I don't think so, especially since I ran the motor already.
    Not enough oil between the bucket/shim/valve? Strange, since the other valves didn't change nearly as much.
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  4. jwalters

    jwalters Farkle Proliferator

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    Have you mic'ed the original and replaced base gaskets? I wish I had more to offer but that's all I can think of.
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  5. Cpt. Ron

    Cpt. Ron Advrider #128

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    Being that it's not a pushrod motor, the base gaskets won't affect the valve lash. The cam chain tensioner will handle any difference in the base gasket thickness.
    #5
  6. jwalters

    jwalters Farkle Proliferator

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    Of course. I wasn't thinking. I'll stay tuned for the solution!

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  7. jwalters

    jwalters Farkle Proliferator

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    Last try: it doesn't seem crazy that your valve lapping compound could have removed the .15mm. You might want to try the same procedure on some scrap and measure the difference.

    Sent from my SAMSUNG-SGH-I317 using Tapatalk 4
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  8. nomad guy

    nomad guy A legal alien

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    Assuming everything is assembled correctly, its an X file case.
    stating the obvious, re-check and set to the correct gap.
    and dont run it over 9200 RPM.:D
    #8
  9. Cpt. Ron

    Cpt. Ron Advrider #128

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    I agree with the first part; yes the compound would/will remove material. But that would move the valve further into the cylinder head/valve face. Which would push the stem further up into the shim/bucket/cam assembly. Thus, reducing the clearance between the top of the bucket and the camshaft.

    But my clearance increased......
    #9
  10. Chewy750

    Chewy750 Adventurer

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    Just lapping the valves in shouldn't cause that much of a difference, nor should there be that much wear and anyway it would be there before you did the work anyway! Just a thought, you haven't put the shims back in the wrong position? One other thought, you aren't a tooth out on the cam position are you?
    #10
  11. Cpt. Ron

    Cpt. Ron Advrider #128

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    When it came apart, every valve and associated pieces were put in individual zip-lock bags and labeled with their position. Upon reassembly (and the ensuing quandary....), I verified the shims to my notes from previous checks and adjustments. I believe having the cam a tooth off could only make the lash tighter, not looser.

    I'll be verifying the whole the again today/tonight. I may end up using locally sourced 9.8mm shims if my shipment of HD shims doesn't come today.
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  12. Keith

    Keith Slabbing it

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    Cam bridge bolts loose?
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  13. Peanuts

    Peanuts Long timer

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    If your feeler gauges are not bent at the end and you check the clearance with one feeler gauge, you will get a smaller figure than with two because the feeler gauges need to flex to get into the gap and the single gauge flexes less than 2.

    So if you used just one gauge in the past, the reading with 2 gauges will appear looser, but its actually operator error ;)
    #13
  14. Cpt. Ron

    Cpt. Ron Advrider #128

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    :huh I'm afraid I don't follow what you're saying. But I've been measuring this machine with the same set of feeler gauges (with bent tips), so any user error should be repeated. I only use one feeler gauge at a time, I don't stack them.

    Lying awake in bed early this morning, I had an epiphany. I wonder if the valve got damaged or bent or something like that. If it doesn't close all the way, that could cause my problem. So, I'm on a quest to find a leak down tester....with a 10mm adapter. No one local seems to stock that. Crap.
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  15. nomad guy

    nomad guy A legal alien

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    What would be the reason for that ? was this cylinder (i am assuming that both those valves are of the same cylinder) off timing at any point?
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  16. Cpt. Ron

    Cpt. Ron Advrider #128

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    No, not that I am aware of. And if it was, it would stand to reason that both of the valves on the mis-timed camshaft would have issues.
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  17. renogeorge

    renogeorge Long timer

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    I don't have an answer but can guess along with the rest. I just adjusted clearance on my 990--removed cams, replaced shims, blah blah. Did not pull head remove valves as you did. Measured clearances were right at the target for the the new shims--no surprise there.

    I can only speculate that dis assembling the head could move things around enough to impact clearance when assembled. Seats are super hard--doubful you changed anything there. Valves--maybe if you really worked hard at the lapping. My guess goes to the valve springs, retainers and keepers--enough metal-to-metal with certain rotation to possibly change the fit and overall height. Machining of these parts along with the spring seating surface could all change the overall height of the valve stem and therefore the clearance once the shim and cam are installed.

    Note to self--when taking head apart, always adjust valves after reassembly.

    FWIW...If anything
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  18. Cpt. Ron

    Cpt. Ron Advrider #128

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    Well, the leak down test did not indicate anything wrong with any of the valves, let alone the one I'm concerned with. So, I'm going to run with it. I re-shimmed it to the larger end of the range, put the minimum parts back on the bike and let 'er rip. It started and sounded sweet after the cam chain tensioners pressurized. It's been too long.

    So the bike will get buttoned up today and taken for a test spin. After some run-in, I'll probably go back in to check the valve lash later this fall.
    #18
  19. jwalters

    jwalters Farkle Proliferator

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    Any update?

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  20. Cpt. Ron

    Cpt. Ron Advrider #128

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    It runs like a raped ape. After checking the valve lash a couple of times just to be sure, I gave up trying to find a problem.
    #20