Rocker Arm Blowout

Discussion in 'Street/strip 400/430/455' started by techg8, May 24, 2018.

  1. techg8

    techg8 The BS GS

    So the BS GS has experienced a rocker arm blowout on cylinder #6

    Springs are single Manley springs right at 300lbs
    I don't rev past 5500rpm most times
    No valve float that I can feel at hi rpm (doesn't nose over at all)
    TA 9.325" pushrods are spotless

    The rockers were a little noisy, especially on cyl 6.

    I am thinking of possibilities...
    poor oiling from cyl 6 lifters
    too much lash on cyl 6 rockers - valve stem height?
    old steel rockers reached the end of their service life

    any other ideas?

    It bears mentioning that the same cylinder did break the tip off a TA adjustable pushrod a year ago or so, set at 9.325" at about 3500 rpm.

    ZERO lash has repeatedly measured 9.310". The drivers side is near silent running 9.325" pushrods. clicking can be heard on the passenger side running the same length.

    here is the latest pic:
    rockerbowout.jpg
     
    Last edited: May 24, 2018
  2. Briz

    Briz Founders Club Member

    Looks like they get plenty of oil.
     
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  3. Rob Ross

    Rob Ross Well-Known Member

    What is the lift? Generally anything over 0.520” ish is hard on those rockers. 69 430 rockers hold up much better. If you run the steel arms, debur the oil hole. That hole looks like it might be pierced and has a sharp edge on it/some.
     
  4. techg8

    techg8 The BS GS

    High .490s lift
     
  5. techg8

    techg8 The BS GS

    Good call. I see that in the pic now.
     
  6. Bens99gtp

    Bens99gtp Well-Known Member

    Steel arms just don't hd up, 400/430 with correct pushrods or bite the bullet and get some rollers.

    It is possible depending on heads deck heights etc to need a different rod side to side
     
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  7. hugger

    hugger Well-Known Member

    Arms were just tired

    I bet if you had them nitrated the service life would maybe double
     
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  8. chrome yellow

    chrome yellow Well-Known Member

    I kept having that problem years ago. New rockers solved it in that engine. They were just old and worn out.
     
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  9. Stevem

    Stevem Well-Known Member

    300 psi sounds high to me for factory rockers !
    If I was to chance running that much open pressure I would send the rockers out to get Cryo treated!

    Also a kind of repeated failure on that same valve would cause me to think that dispite having 300 psi of open pressure that valve spring is not controlling the valve action as it should and your hammering that push rod into the rocker at certain rev's.
     
  10. techg8

    techg8 The BS GS

    It is suspicious that trouble repeated on the #6 cylinder. I hadn't thought to suspect the valve springs, thanks.
     
  11. techg8

    techg8 The BS GS

    I just found a damaged rocker on the driver side, cyl #1.

    Same failure mode as cyl 6 which failed previously.

    This is good in that the failure is no longer isolated to one cylinder.

    This leads me to believe that the old steel rockers are indeed just tired out.

    So i've installed a new set of steel rockers. And I am sticking with the 9.325" pushrods.

    We had measured carefully, several times, to determine the correct pushrod length, so I am trusting those numbers.
     
  12. Jim Weise

    Jim Weise EFI/DIS 482

    70-71 alum 455 rockers would be the best choice here.. plenty durable for any most all flat tappet cams, and they don't require the hybred pushrod the 67/9 stuff does, I save those for mild roller cams.

    I have had that pushrod break thru on those rockers on brand new ones.

    JW
     
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