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Longer pushrods and the effects....anyone know?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by twenty_below0, Aug 23, 2002.

  1. twenty_below0

    twenty_below0 1/2 ton status

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    I put a set of roller tip rockers on my new engine and they were suppose to be 1.6 ratio, so I bought .100" longer push rods as I was told to do by summit. The rockers were from a private party, I have never seen the 1.6 ratio rollers ( steel rollers like the Comp ones) so I am wondering if these are actually 1.5 and I put the longer pushrods on with them. How can I tell and what would happen if in fact they are only 1.5 and I put the wrong LONGER pushrods in? Would it cause pre-mature floating of the valves or something? And if they are 1.6 how do you tell will they look different ,(like the regular long slot 1.6 rockers look funny at the ends)
     
  2. BigBurban350

    BigBurban350 1/2 ton status

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    Check valve lash specs. Use a feeler guage to measure between the roller tip and the valve butt. Make sure the valve is in the rest position. Longer pushrods will decrease valve lash.
     
  3. twenty_below0

    twenty_below0 1/2 ton status

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    Decrease???which will make them over tight or to loose, I put them in by running them down till I felt resistance then 1/2 turn more as the book suggested. would it change if they were to long....could I have tightened them to much? THX I appreciate this!
     
  4. OLDSTEEL

    OLDSTEEL 1/2 ton status

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    Decreasing the lash means making them tighter
     
  5. 84_Chevy_K10

    84_Chevy_K10 Banned

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    The length of pushrods affects where the rocker arm touches the valve. The idea is to keep it as close to the center as possible.

    I can't see why changing to 1.6 rockers would necessitate changing to longer pushrods. Check your valvetrain geometry.

    Pushrod length has nothing to do wish lash, really.
     
  6. m j

    m j 1/2 ton status

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    wow
    I agree with all of that post
     
  7. BigBurban350

    BigBurban350 1/2 ton status

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    Yes, to adjust valve lash and you have bottom out the rockers, getting extended pushrods will make lash tighter.
     
  8. 502Burban

    502Burban 1/2 ton status

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    Do yourself a huge favor and take a trip to your local magazine rack to pick up the latest (October 2002) issue of Chevy High Performance magazine. There is an article covering this exact issue in there. Very informative and explains in detail how to get your pushrod lengths correct.

    Like 84ChevyK10 said, it isn't a horsepower issue so much as maintaining proper valvetrain geometry. If it isn't right, you will go through valve guides very fast. If it REALLY isn't right, you will possibly break parts (don't ask me how I know this /forums/images/icons/shocked.gif ).
     
  9. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    502 burban, may i have the motor in your pic to the left...
    he he he, i need one ya know...
    grant
     
  10. twenty_below0

    twenty_below0 1/2 ton status

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    THX for all the info I will go get one of these mag's you mebtioned today and figure this out.I still want to know which rockers I have......hopefully I can find a pic of both so I can decide which I have, I did notice the rollers are sitting more to the outer edge of the valve stem but thought they would role in as they compressed...perhaps not?
     
  11. m j

    m j 1/2 ton status

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    the ratio is distance from pushrod to rocker pivot vs distance from valve to pivot
    to change the ratio they move the pushrod closer to the rocker pivot
     
  12. twenty_below0

    twenty_below0 1/2 ton status

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    you wouldn't know the different measurements would you....for ea. ratio? I didn't know that, I thought from the look of the old school 1.6 rockers without the roller it was in the design or height of the tip that touches the valve stem. If they were just closer to the pivot why would you need to run the longer pushrods?
     
  13. m j

    m j 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    If they were just closer to the pivot why would you need to run the longer pushrods?

    [/ QUOTE ]

    as I have never heard, until you posted, that anyone had to run longer pushrods you are going to have to tell me.
    I dont think it is ratio dependant but may be your roller rockers are different then standard rockers
    you can buy normal looking rockers that are 1.6, very common low buck item.
    never heard of longer pushrods being used with them.
    what other changes are required to run your rockers?

    I bolted 1.73:1 cleveland rockers in place of my 1.6:1 in my 5.0 ford motor. no pushrod changes required
     
  14. 502Burban

    502Burban 1/2 ton status

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    m j
    I don't think that the necessity for longer/shorter pushrods is directly related to a different rocker arm ratio. But, IIRC changes will be required due to things like having the block/heads decked, valve jobs that sink the valve deeper into the head and raise the valve stem height, head gasket thickness, variations in manufacturer rocker arm design and also cam base circle diameter. I would imagine that rocker arm ratio could have a small impact one way or the other.


    twenty below0
    If your rocker arm roller tips are toward the outer edge of the valve stem while the valve is closed, then your pushrods are too long. The tips should be just inboard of center, ideally. That way it will roll across the center by about the same amount as the valve opens. This whole pushrod length thing is something I always check on anything I build now. Learned the hard way on a small block Ford years ago after breaking all kinds of fun valvetrain parts. /forums/images/icons/frown.gif

    Seventy4Blazer
    I don't know... I've grown kinda attached to the big lump.
    I really want to hear it run. Maybe if it doesn't go... /forums/images/icons/wink.gif
     
  15. twenty_below0

    twenty_below0 1/2 ton status

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    I plan on putting a set of Canfield heads on in the near future probly about 10,000 miles from now will they hold until then as long as I dont run to many rpm's.? thx for the responce.
     
  16. 502Burban

    502Burban 1/2 ton status

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    It'll probably depend on how far off they are right now. Although, unless you've done a lot of machining to this engine, you will probably be fine for a while. This isn't as big an issue for a lower-revving truck engine as it would be for an 8,000 rpm small block in a drag or endurance engine.

    As long as the roller tip isn't trying to roll of the edge of the valve stem, you should be OK until the Canfield heads upgrade. You would probably want to get everything correct at that time.

    Take care,
     

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