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Effect of tight exhaust valves?

Discussion in 'XJ Technical Chat' started by iX., Jul 19, 2015.

  1. iX.

    iX. Member

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    Having just measured all the valve clearances on my recently acquired Maxim-X, I have determined that somebody did a valve job on it using clearances for a non-X head. All exhaust valves come up between .006" and .008" (spec for all two valve airheads under 1100cc) rather than .008" to .012" where they should be for the XJ750XN 5-valve waterhead. All intake valves are in the .004" to .008" range as specified.

    My question is, what would the net effect of that likely have been?

    -iX.
     
    iX., Jul 19, 2015
    #1
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    valves open for longer duration. more ware on cam and it bearings. lower comprestion and performance.

    my opinion of valve specs is that Yamaha wanted its motors to run with the wider gap.
    otherwise it would have been a + or - tolorance , and you could buy shims to put gap midway to the spec.
     
    XJ550H, Jul 19, 2015
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  3. fiveofakind

    fiveofakind Well-Known Member

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    does your bike backfire at all ? I would surely get those valves within spec if I were you.....one can not properly adjusted carbs without valves in spec....
     
    fiveofakind, Jul 19, 2015
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  4. iX.

    iX. Member

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    Oh no question I will be putting them to spec, tool is on the way. I'm just wondering what the effect WAS of running that way. No plans to keep them out of spec.

    The bike wasn't backfiring, no.


    -iX.
     
    iX., Jul 19, 2015
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  5. Polock

    Polock Well-Known Member

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    after a few minutes of hiway riding then a red light the internal temps go up, the valve train expands and the valves can't seat, the motor stalls and won't start until it cools a bit.
    the worst case is a long hiway ride with the valves just barely seating and then start leaking a few places letting tiny jets of fire go between the valve and the seat, doesn't take long for the fire to do bad things to the aluminum valve seat
     
    Polock, Jul 19, 2015
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  6. BigT

    BigT Active Member

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    Burning the exhaust valve is a possibility due to the valve spending less time in contact with the valve seat. Heat is transferred from the valve to the valve face and through the head to the water jacket.
     
    BigT, Jul 19, 2015
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  7. iX.

    iX. Member

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    I didn't see any of those symptoms so hopefully that means it this amount of tightness isn't excessive.

    How do you detect burnt valves? The cam cover is off right now, can you tell with a visual inspection?
     
    iX., Jul 19, 2015
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  8. Polock

    Polock Well-Known Member

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    you could do a compression test or better yet a leak down test
     
    Polock, Jul 19, 2015
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  9. BigT

    BigT Active Member

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    Not sure about visual indicators, but a loss of compression can be a symptom of a burnt valve.
     
    BigT, Jul 19, 2015
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  10. iX.

    iX. Member

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    Planning on a compression test after the valve adjustment is complete. I suppose given that we fabricated an adapter for the compression tester out of a gutted used sparkplug we could do the same for a home-made leakdown tester.

    -iX.
     
    iX., Jul 19, 2015
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  11. XJ550H

    XJ550H Well-Known Member Premium Member

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    you can make your own color tune too. recent thred about it
     
    XJ550H, Jul 19, 2015
    #11

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