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Thread: Valve stem oil seals.

  1. #11
    Super Moderator ancientdad's Avatar
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    I think Tools reference is to excess valve guide wear on the exhaust side when seals are used, reducing the lube down the guides
    Tom

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  2. #12
    Senior Member TOOLS1's Avatar
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    Quote Originally Posted by ancientdad View Post
    I think Tools reference is to excess valve guide wear on the exhaust side when seals are used, reducing the lube down the guides

    Yes!. You really need that extra lubrication on the exhaust valve and guide.
    TOOLS

  3. #13
    Senior Member FrisianWheel's Avatar
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    Valve stem oil seals.

    Quote Originally Posted by TOOLS1 View Post
    Yes!. You really need that extra lubrication on the exhaust valve and guide.
    TOOLS
    Makes sense to me but would you recommend to put valve guide seals only on the intake valves on Honda twins in general? Just to be sure.
    Gunnar

    1972 CB450 K5
    1975 CB500T
    1972 CB450 K5 - in progress

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  5. #14
    Senior Member TOOLS1's Avatar
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    If you really want valve guide seals in your engine (maybe to meet emission requirements), only put them on the intake valves.
    TOOLS

  6. #15
    Senior Member Richard_Pitman's Avatar
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    Quote Originally Posted by TOOLS1 View Post
    If you really want valve guide seals in your engine (maybe to meet emission requirements), only put them on the intake valves.
    TOOLS
    I'm agonising over how to put this question without sounding confrontational or deliberately argumentative, hope you'll bear with me on this.

    Honda themselves specify oil seals on the exhaust valves only, which does seem odd to me, as most engines I've been into have seals on both inlets and exhaust. Why did they do it this way ?

    The CB200 engine, which is very similar, albeit with different valve guides, has oil seals on both inlet and exhaust. Would the same advice apply to that engine ?

    It was my understanding that worn inlet guides were the cause of oil smoke in the exhaust, hence TOOLS comment about emission requirements ?

    Worn exhaust valve stems / guides ? Presumably a finding based on experience ?
    1970 Honda CB175K4
    1972 Honda CL175K7
    1999 Honda CB600 Hornet
    1970 - 1972 Random heap of CB/CL/SL 175 parts, slowly being reassembled ..

  7. #16
    Senior Member TOOLS1's Avatar
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    OK, here it is. In all the Honda twin heads alone that I have done work on, the CB 350 heads do not have valve guide seals and the only time I have had to replace a valve guide was because of physical damage, like a bent valve. The CB 360 uses the same valves as a CB 350 but has valve guide seals on it. Every CB 360 I have worked on has needed new exhaust valve guides. Hence, I have determined that by not having a seal on the exhaust valve guide that the slight lubrication provided to the exhaust valve and guide has enabled them to last much longer.
    TOOLS

  8. #17
    Senior Member Richard_Pitman's Avatar
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    Thanks, that makes sense.

    Would it be fair to say that Honda fitted valve seals on the later engines in the interest of oil control / emissions, with the unintended side effect of increased guide wear ?

    One of my 175 heads had a pitted exhaust valve seat, too deep to be lapped out with grinding paste, so I took it to a local bike shop who have a small machine shop, able to rebore cylinders etc. I was hoping they'd be able to recut the seat on their machine, but in the event the chap there did it manually, with some sort of diamond cutter. Anyway, it did the trick, so far as getting a good valve seat was concerned. He also touched up the other three seats and reassembled the head, not that I'd asked him to do this.

    In conversation afterwards, he said that in an ideal world, new valves and guides would be fitted, but 'for an old engine like yours, and what you use it for, it's not worth it'. I had to agree, 50 UKP for the work he'd done vs several 100 UKP for valves, guides and fitting.

    Engine runs fine, doesn't smoke or use oil. However, as the guides are already slightly worn, I reckon running it without stem seals would let oil too much oil pass through. Matter of balancing short term oil issues with long term further wear, on an engine that's only going to do 2-3000 miles per annum.
    1970 Honda CB175K4
    1972 Honda CL175K7
    1999 Honda CB600 Hornet
    1970 - 1972 Random heap of CB/CL/SL 175 parts, slowly being reassembled ..

  9. #18
    Senior Member FrisianWheel's Avatar
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    Valve stem oil seals.

    Thanks for the explanation Tools. Makes sense but I get Richard's point as well. I'm confronted with the very same question for my 450 project and see an imaginary Yoda above my head, saying: Decision make you must.
    ancientdad likes this.
    Gunnar

    1972 CB450 K5
    1975 CB500T
    1972 CB450 K5 - in progress

  10. #19
    Senior Member LashLarue's Avatar
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    What are the symptoms of a worn exhaust seal? Will it smoke?
    Mike

    CT90 (2)
    SL350 - k1

  11. #20
    Super Moderator ancientdad's Avatar
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    Yes, worn valve guide seals allow excess oil down the valve stem and it burns off with the exhaust heat, but badly worn valve guides can cause it too - as well as poor compression if worn badly enough
    Tom

    CL450 project reboot, street legal this time
    Budget drag bike project
    CB350K1 full patina project
    Ride along at the drag strip


    running points... because I'm too old for mysteries that begin with pushing

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