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0-200 exhaust rocker not contacting all of valve stem

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  • 0-200 exhaust rocker not contacting all of valve stem

    Got an 0-200 that the rocker arm tips are not contacting all of the exhaust valve tips . None of the rocker arms are the new part numbers which are shown to be intake and exhaust specific. TCM SB M77-19 states the exhaust are the only rockers with the oil hole. Any body run into this problem?

  • #2
    You're question is confusing. Are any or all the rocker arms not contacting the valve stems (a gap exists), or are they offset from the center of the stem top where they make contact? I've seen that and assumed it was to force the exhaust valve to rotate. Are any of the rockers drilled and have an oil outlet hole near the valve stem? Or are all of them with drilled holes? I've seen the last condition - all 8 are drilled with holes and none are intake valve specific without holes.

    Gary
    N36007 1941 BF12-65 STC'd as BC12D-4-85

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    • #3
      They are offset to the stem, you can see part of the valve stem, will check on all oil holes. Offset like this will cause premature failure/wear of the valve guide. The #5 ex guide/valve is shot.

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      • #4
        Thanks that's clear. There's a Taylorcraft C-85 in a shop here with (If I recall correctly) offset rockers at least on one but maybe more of the exhaust valves. The intakes weren't as offset (IIRC). I was a bystander and not the mechanic doing the exam. One exhaust valve had stuck and then was later forcibly released. On removal the valve stem and guide were noted to be carboned and the guide apparently worn allowing the valve some excessive wobble. The valve and guide were't cleaned and measured yet for tolerances. The mech looked at the others but I don't recall if the rockers were offset. Engine about 900hrs SOH.

        Question: What's the source of the offset? Is it due to mechanical tolerances at build or due to wear over time?

        Gary

        N36007 1941 BF12-65 STC'd as BC12D-4-85

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        • #5
          Click image for larger version

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ID:	186453 Will post pictures Monday.. Called Continental and sent them pictures, they said it was safe to run this way. Click image for larger version

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          Attached Files
          Last edited by at7615; 03-02-2020, 18:52.

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          • #6
            Any misalignment with the rocker shaft during bushing installation or a guide C/L off a little bit will add to the misalignment. I've had success in replacing the rockers to get a better alignment. The rocker should not be in full alignment with the valve stem. A slight offset is needed to cause the valve to rotate when under lift. Helps keep things clean and oiled in the stem area.
            EO

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            • #7
              Good pics and thanks for the reference from Continental as being ok for all. Edwin notes a slight offset is preferred to help rotate the exhaust valve. Now we have a basis for comparison. It looks to me like Pic #3 from top has more oil cooking near the valve - maybe from some developing exhaust guide leakage (?) - and slightly more rocker-stem offset maybe from valve guide or rocker bushing wear (?). That's what the local that stuck a valve looked like but worse - both oil cooking and offset.

              Great info?

              Gary
              N36007 1941 BF12-65 STC'd as BC12D-4-85

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              • #8
                Unless they have rotators, I have never seen a small continental valve rotate. I am not saying it doesn’t happen, I just have not seen it. Swap the rocker and use some Prussian blue the valve tip and see what the valve contact is. Then make a decision. Tim
                N29787
                '41 BC12-65

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