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Thread: K valve clearance

  1. #1
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    K valve clearance

    It's winter now, and I'm out in the garage playing with my K1 sidecar rig. With all the plastic off, I've checked valve clearance, and found the intakes at .006 and the exhausts at .008 in. The books call for intakes at .006 to .008 in. and exhausts at .010 to .012 in.

    The valves were last adjusted by a mechanic at a BMW dealership, about 20,000 miles ago. I'm wondering whether all the valves have closed up at exactly the same rate, or whether the mechanic set them closer than my specs call for.

    And, since the old beast has to pull a sidecar around, I decided to pull the driveline out and check the U joints. I had heard some scuttlebut from the K1 guys about exploding U joints at about 40,000 to 50,000 miles. All the Paralever pivot bearings are notched and need replacing, and I'll do the boots too. There is no perceptible sticking or clicking in the U joint bearings, but should I replace the U joints now? I have to assume they are expensive, and the forward U joint seems to be part of the drive tube, for more bucks.

    Anyone got advice on these subjects?

    pmdave

  2. #2
    Blocking the slow lane
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    Regarding the valve clearances.....yeah, its possible that the clearances were close at the last check, so the mechanic left them alone to save you some money. Pull the cams and do them all this time....you might even be able to swap some of the tappets around and get the clearances you need without having to order all of them from the dealer.

    Regarding the driveshaft.....is replacing both pieces now less expensive than a tow later on? I guess it would depend upon your service use....mostly around the peninsula, or do you wander far from home with this rig?
    Jon Diaz
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  3. #3
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    Jon, thanks for the quick come-back.

    Since I was given the long distance sidecar award at the Trenton MOA rally, we could definitely agree that I do more than putting around the neighborhood.

    But the repair manuals say to check the U joints for smoothness, free play, and spline wear, and replace if not correct. I feel the joints, look at the splines, and they look and feel excellent, with no free play.

    So, I'm looking for some failure experiences. Do the K bike U joints fail catastrophically, or do they fail when the cross bearings wear out? Do you hear/feel some indication? And what's the expected life of the U joints, given "extreme" service (as in pulling a hack)?

    Scuttlebutt from the K1 guys is (to paraphrase) "the U joint just let go. The only warning was a strange noise for a while before it broke."

    over...

    pmdave

  4. #4
    Blocking the slow lane
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    Originally posted by pmdave
    So, I'm looking for some failure experiences. Do the K bike U joints fail catastrophically, or do they fail when the cross bearings wear out? Do you hear/feel some indication? And what's the expected life of the U joints, given "extreme" service (as in pulling a hack)?
    I've replaced two driveshafts on my 180K-mile K75. In both cases, the driveshaft u-joint had simply tightened up, and we found it during a random spline lube.

    I imagine if the u-joint were about to fail, you could feel a vibration on the swingarm housing, but that's pretty tough to touch with your foot while you are riding down the road. If they feel fine now, that's pretty much all you have to go by.
    Jon Diaz
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  5. #5
    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    ditto

    I agree, now would be a good time to "optimize" your valves. You might get away with leaving the intakes alone, but definitely do the exhausts at least. The old saying, "rather hear them than smell them" applies, but getting them back in spec would be a good idea. As far as the U-joints, in addition to figuring the relative values of the joints-vs-cost of a tow, factor in your peace of mind. Along those lines, as long as you've got it out.....new parts aren't that expensive. Rather now than do it over later.

    That's my nickel's worth. (inflation, you know!)
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  6. #6
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    OK wrench pals, I decided to get all the valves within spec. The K1 uses valve buckets of different thicknesses. No shims to fall out of position. What I discovered is that the "shims" come in increments of 0,05mm. So, if you're right at one of the limits, say 0,15mm, changing to the next size shim would put it at the other limit, 0,20. But if you're just a bit under, say 0,14 changing to an 0,05 thinner shim would put it at 0,19, just under the upper limit. I'm not so concerned about the intakes being at the tight end of the limit, but I'd rather have the exhausts at the loose end of the limit.

    In other words, you can't optimize the valve lash in the middle of the range, you can only get it within the spec range of 0,05 mm.

    Yep, I'll be ordering three shims. Only one will swap where needed. Around $14 ea.

    And, as I was waffling over the phone about the $390 price of a new driveshaft with U joints, I decided it was only money, and went for the deal. So, the old sidecar rig is quite a mess at the moment, with little piles of valuable innards spread around, covered with towels to keep the dust at bay. Wow, with 16 valves, two cams, and ten cam bearings, that's a lot of parts, and nothing can be mixed up.

    So, thanks for the advice. Visa will thank you later.

    pmdave

  7. #7
    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    Like I tell the customers at the shop I work at, I'm not trying to spend your money for you, just point out options and alternatives. Ultimately it's the customer that makes the decision. I do try to let them know what I would do, if it was my bike. In fact, I took my K-bike to the dealer 2 years ago, just to have another set of eyes look it over, and told them to make believe it was their bike. There were certain things I wanted
    done, but if there was something he saw that needed attention, I asked for a call. I don't regret it.

    See ya in Spokane!
    Last edited by manic mechanic; 11-06-2003 at 11:46 PM.
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  8. #8
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    "manic mechanic" make a really good comment about having a second set of eyes look over your bike. That same comment can apply to cars, certainly aircraft, boats and maybe even nuke plants. If you have ever done this, you'll know the wisdom of which he speaks. If you never have done it, you're missing something.

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