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early hemi pushrod clearance

Discussion in 'The Hokey Ass Message Board' started by AngRi, Aug 8, 2013.

  1. AngRi
    Joined: Aug 26, 2004
    Posts: 33

    AngRi
    Member

    Hi,

    I've been rebuilding my '57 392 hemi this summer and everything has been going really well (and slow) - so far. Last night when I was installing adjustable pushrods, stock 5/16" width, I noticed some exhaust rods being pretty badly offset going through the heads. And always offset towards the stands. They are not quite rubbing the head, but they are really close and might rub when engine is hot. I've read people usually grinding the holes bigger for 3/8" pushrods, but since these are stock width, I was not planning on doing that and was not expecting to see any issues either.

    I'm wondering what could be the cause of this. When I first rebuild the heads a while ago, the rocker shafts were filled with sludge so there were some oil circulation issues in the valve train. Would it be possible that exhaust rockers wore out more by rubbing with rocker stands because of lack of oil? Wouldn't think that swapping rockers between the left and right bank would make any difference, but will be testing that tonight.

    Looking at possible fixes I'm wondering if I could move the offset pushrods by shimming the exhaust rockers with chrome-moly shims. Anybody see any issues with using shims between the rockers and stands? At this point I don't want to start grinding the holes bigger, if there's a way to avoid that...

    Thanks!
     

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  2. 73RR
    Joined: Jan 29, 2007
    Posts: 6,545

    73RR
    Member

    How close is "really close"?

    I have seen plenty of stock pushrods with slight wear/rub marks but no real damage/issues.
    Yes, you could enlarge the holes. I suggest an angled cut, on the offending side of the hole, from the top to about the center of the length of the hole, perhaps 0.060" at the top and taper to '0' at the mid-point. Do this in a milling machine with an end mill that is similar in diameter to the hole.

    You can shim the rockers if they only need to move fore/aft. TR Water also sells locking collars if you have room for them.

    .
     
  3. PackardV8
    Joined: Jun 7, 2007
    Posts: 890

    PackardV8
    Member

    If they're not touching anywhere as you rotate the engine, you'll be fine. Think pushrod guide plates. People pay good money to have some steel rubbing against their pushrods.

    jack vines
     
  4. 270dodge
    Joined: Feb 11, 2012
    Posts: 742

    270dodge
    Member
    from Ohio


  5. AngRi
    Joined: Aug 26, 2004
    Posts: 33

    AngRi
    Member

    It's pretty hard to get exact clearance, but in the worst case when I stick 22 gauge wire to the tightest spot, the gap between the rocker and stand is tad over 0.02", so I'd say the clearance is between 0.01"-0.008". Pressing the pushrod towards the closest point I can make it touch the head. But it's not touching w/o force.

    I'm thinking that shimming is the way to go here, if shims are not going to cause any long term issues. It'll give a little more playroom and peace of mind... If I place a 0.03" feeler gauge between the rocker and stand, I'm getting pretty much 0.04" clearance as the tightest spot is @ 8:30 o'clock looking horizontally with exhaust shaft. Also rocker tip will still sit nicely on the valve stem.

    About cleaning the rockers, yes absolutely they are clean inside out with every hole gone through with wire/drill bit, lacquer thinner/brake cleaner and forced air. Hemi Haines guide has been a great resource in my build.

    Thanks for the comments!
     
  6. 270dodge
    Joined: Feb 11, 2012
    Posts: 742

    270dodge
    Member
    from Ohio

  7. hemiphil
    Joined: May 6, 2010
    Posts: 25

    hemiphil
    Member
    from australia

    when running 3/8" adjustable pushrods, if you use high lift cam, you may have to drill pushrod holes to 1/2", i had to drill my heads when using crane roller .615" at valve. also when i built a 354 hemi with hot heads roller rockers, the adjusters were out to far which caused the push rod to bend on full lift, changed push rod length and drilled heads for more clearance.
     
  8. I'm running 3/8 pushrods with stock valvetrain geometry and roughly .530 lift. I've got a few pushrods that rub ever so slightly but it's no problem at all.

    [​IMG]
     

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