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Help, valve adjust gone technical

Discussion in 'The Garage' started by adaycj, Jul 16, 2007.

  1. adaycj

    adaycj Been here awhile

    Joined:
    Aug 25, 2003
    Oddometer:
    563
    Help.

    I am in the middle of a valve adjustment on my ZRX 1200. It is a "shim style" with the shim on top of the valve. The cam acts on a rocker and then directly on the shim. I have a dilemma. I have seen two methods to position the cams to test the clearances. One involves using the advancer marks, AKA the "shop manual method". I have the manual and I used this method. I also used the "cam lobe up" method. The logic behind the cam lobe up method seems to be that the extra turning of the crank is better/easier because the cams all get measured in exactly the same position. Also you do not need to line up marks because you can see the lobes as you turn the engine.

    The problem is that the readings are different using the two methods. On two of my lobes they are .002 inches different. On several others they are .001 inches different. This changes the shims needed for the job, and makes me wonder. Which is best, and what should I do?

    One theory I have is that as long as I am no where near the ramp and there is "at least" adequate clearance that things should be ok. My only argument here is, what if the clearance of .002 inches less is somewhere else on the base circle and this doesn't leave the valve fully seated when the engine is fully warm? The full range of the spec is only .0025 and the shims do not come in fine enough increments to make the lash always stay in spec.

    Another theory is to test each valve in three places on the base circle and replace shims as needed to maintain at least the minimum spec. The full range of the spec is only .0025 inches and the variance is .002 on two of my base circles on my cam. But man, I feel like I am making a ZRX valve adjustment into a Hubble mirror alignment.

    Also before you reply. I am a mechanic. I have done many dozens of valve adjustments on cars and a few on motorcycles. I have go/no-go gauges and I have verified all of my readings in every position at least twice, on two separate visits to the engine. I am measuring between the shim and the rocker, per the service manual (not the cam and rocker). I verified my feelers with a mic and verified my mic with a caliper. I have the equipment and the skills to get repeatable readings. I just don't know what to do when the base circle of the cam is not true to the bore. Or there is another phenomena that is occurring you can enlighten me about?

    And before you worry about me, I have two other motorcycles to ride :rayof . I'll be ok if this takes some time to sort out. Help.
    #1
  2. matey peeps

    matey peeps Bead Buddy

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    #1. 1/1000 of an inch is not really something to get your pants in a bunch over.

    #2. If I were in your situation, I'd always err on the side of 1/1000 loose valve clearances instead of 1/1000 tight.
    #2
  3. Scottysix9

    Scottysix9 Shhh...

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    Follow the procedure in your manual if it is a Kawasaki Service Manual. Lobe up is good, but some Kawasaki's can be picky about valve adjustment so it's always best to follow the procedure KMC recommends.
    #3
  4. markjenn

    markjenn Long timer

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    You're the first person who has confirmed exactly what I noted when I checked valves on my ZRX1100 (same engine).

    The problem you are noting is called "cam base circle tolerance". The cam base circle is the diameter of the cam journal without the lumpy lobe part that opens the valve. Ideally, it should be perfectly circular so that you get exactly the same clearance at any point where you measure in which the lobe is not bearing on the bucket. But because of tolerances in machining, it is not perfect. The generally accepted tolerance in cam base cricles is about .001 for most engines, but .002 is not terribly uncommon in car engines according to some sources I found on the net. I've done a lot of shim-adjusted engines and the ZRX is the first where I noted enough of a variance to affect whether to shim a valve or not; I don't know if that means the ZRX/ZX-11 motor is particularly loose in this tolerance or not.

    When I first did a valve check on my ZRX, I simply pointed the lobes 180-deg away from the buckets and measured. I was surprised that about eight valves were out of spec. So I measured the clearances again using the "by the book" method. Five of the eight valves now were within spec. Like you, I pondered what to do. So I did some reading on tolerances, and decided that since the bike was used that perhaps the previous owner had adjusted them using the book method or maybe they used the book method at the factory. If so, then my adjusting all five of the eight might simply be me chasing tolerances in cam base circle. So I did it by the book and changed shims on three valves.

    In reality, I suspect that no matter how you do it, you're probably within the tolerances allowed in the valve clearance so it doesn't matter that much. If you want to get anal about it, I'd probably use the method which causes the valves to be on the loose side rather than the tight side. But mostly, I think the thing to do is to be consistent between adjustments so that you're not swapping shims back and forth to cover your own variances in where you measure the clearance. In my case, the book method was the definitive method and resulted in the least amount of work, so I used it.

    I sold the bike a year later so I never had a chance to measure them again.

    - Mark
    #4
  5. motu

    motu Loose Pre Unit

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    I'm a ''base circle'' man myself,and have noticed this too...much to my annoyance.I reckon there can be nowhere better to check valve clearance than 180 degrees away from the lobe point....but sometimes clearances are wider just before the ramps.Deposits can build up on the back of the cam lobe too because there is no metal contact.I still set my clearances on the back of the cam,but double check say 30 degrees either side to see if they go wider.If there is a noise issue I'll set them where they are widest.It's OK to fiddle around when you have screw adjustment,but shims are something you want to set only once.
    #5
  6. adaycj

    adaycj Been here awhile

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    I have revisited this several times since the original measurements. I found that I can use a shim one step thinner on 3 valves with a "cam base circle tolerance" of 1 thousandth. Another way to put this is that I am going to use a thin shim that matches the thickest part of the cam base.

    I can also do this with one of the .002 inch cam base circle lobes. That leaves me with one problem. A valve with a cam base circle tolerance that will either leave me too tight at some point with a thick shim, or too loose at some point with a thin shim. I'm going to set it loose and listen to it. If there is no noise (ticking) hot or cold, then I will leave it. If it is noisy, I will add the next thicker shim. After I work all that out I will cover it all up with a nice carb balance.

    An added benefit is that I can buy two shim refill kits to get all the shims I need. Any other approach requires another $40 kit.

    I would just buy an aftermarket cam set, but the engine just runs so good. I really don't want to start another round of tuning. There are many reports of pitting with these cams. After witnessing the quality at this point, the pitting won't surprise me at all at the next adjustment.
    #6
  7. markjenn

    markjenn Long timer

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    Wow, you're really getting into this. I don't think it is that critical, but you're certainly going to be fine when you're done. Carry on.

    - Mark
    #7
  8. furiousfart

    furiousfart Been here awhile

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    Why not check the compression for each cylinder, and adjust your shims to even them out. If worrying about the roundness of the cam just adjust to the middle of the range and check the compression and adjust again from there.

    Me I'd just adjust it the same way every time and just not worry about it any way. It's all a feel thing any way.
    #8
  9. adaycj

    adaycj Been here awhile

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    In a previous life as an automotive engine test engineer I did a study on engine cranking compression. No way possible that any system I have access to could quantify the cylinder pressure changes that would result from a thousandth or two change in valve clearance. Well, as long as the valve still closed...

    After all, all I really need is a valve clearance setting that will allow the valves to fully close and transfer heat away when everything has expanded without making a racket. I leave the spec up to the engine manufacturer. Since my cams are poor, now I have to guess at the best plan to apply the spec. The thing ran just fine with almost every valve several thousandths under spec, I'm sure it will run fine with any reasonable attempt at setting the valves in spec.
    #9
  10. GreaseMonkey

    GreaseMonkey Preshrunk & Cottony

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    Personally, I'd set them at 180 degrees and be done with it.

    If it kept me awake at night, I'd look up somewhere what the valve lift is supposed to be, and measure it with a dial indicator at the valve stem. If the measured lift was on the short side I'd re-think that setup but I really doubt that would be the case.
    #10
  11. Poolside

    Poolside Syndicated

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    <BR>Yeah man, you're going all this way and you aren't using a .0001" linear dial gauge? Weak :lol3



    I am SO joking with you. You could be in much worse shape, you could have a motor with shim-under-bucket. At least the Necco Wafers are easy to pop in and out.
    <BR><BR>
    #11
  12. motu

    motu Loose Pre Unit

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    Well I'm doing the DTI and magnetic base next - poking bent feeler gauges down a hole is frustrating and not accurate.
    #12
  13. motu

    motu Loose Pre Unit

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    I've just checked my valves with a DTI (XT600,rockers with screw adjuster tappets) and it appears they are tighter than what I set them to with feeler gauges.I'm still not satisfied with this method either,the needle seldom lands in the same place - it's a bit cramped and I'd need to pull a few more things off to get a good,or better angle onto the rocker.But I thought I was wildly too wide on one exhaust valve,and the DTI has it on the tight spec,the other is 0.05mm tighter.

    So from that I think the DTI is too much hassle,feeler gauges are near enough....and near enough is good enough on something like an XT600.
    #13