Pushrod length/rocker geometry
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Pushrod length/rocker geometry

  1. #1
    Member Romper Stomper's Avatar
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    Default Pushrod length/rocker geometry

    I've got to determine the pushrod length on a Pontiac motor and I'm not sure what to do. I know you run the cam to mid-lift and make sure the rocker is 90° to the valve stem and the roller centerlines match up. My problem is, I'm using a skid ball rocker with a roller tip and I'm not sure where the skid ball centerline is. Im thinking it would be at the top of the ball/base of the polylock. Any suggestions? Thanks in advance.

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    Quote Originally Posted by Romper Stomper View Post
    I've got to determine the pushrod length on a Pontiac motor and I'm not sure what to do. I know you run the cam to mid-lift and make sure the rocker is 90° to the valve stem and the roller centerlines match up. My problem is, I'm using a skid ball rocker with a roller tip and I'm not sure where the skid ball centerline is. Im thinking it would be at the top of the ball/base of the polylock. Any suggestions? Thanks in advance.
    For what you're doing, that's going to be plenty close. If somehow you can figure the radius of the ball, then you could use that but I think you're going to be fine.
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    gn7
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    Although 2 balls stacked atop each other isn't a perfect sphere, the top of the ball is close enough for the type of rocker, and the lift you are dealing with.

    However I will warn you that many of those rockers are just copies of the original stampings with a longer slot. Many(most) OEM stamping were designed around the 1/3-2/3 arrangement, Be sure you don't run of slot if the PR has the rocker starting somewhere other than the full closed end of the slot.



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    Last edited by gn7; 07-15-2013 at 12:21 PM.

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    Does this look ok?
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    Quote Originally Posted by Romper Stomper View Post
    Does this look ok?
    How much lift? Push rod looks a little long. I like the '56 better...
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    Quote Originally Posted by steelcomp View Post
    How much lift? Push rod looks a little long. I like the '56 better...
    The cam card says .510/.520, but I'm getting .524/.534 on the retainer.

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    Quote Originally Posted by Romper Stomper View Post
    The cam card says .510/.520, but I'm getting .524/.534 on the retainer.
    do the math on the rocker on both ends! If you are running a 1.7 rocker the cam lift is .305/ 314. Then do the x 1.7 to get lift at the valve.

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    Quote Originally Posted by ol guy View Post
    do the math on the rocker on both ends! If you are running a 1.7 rocker the cam lift is .305/ 314. Then do the x 1.7 to get lift at the valve.
    Read my original post. It's a Pontiac. Most Pontiacs use 1.5 or 1.65 ratio rockers. I'm using 1.5. Cam lift is .340/.346. I'm sure you can math up the rest...

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    Quote Originally Posted by gn7 View Post
    However I will warn you that many of those rockers are just copies of the original stampings with a longer slot. Many(most) OEM stamping were designed around the 1/3-2/3 arrangement, Be sure you don't run of slot if the PR has the rocker starting somewhere other than the full closed end of the slot.
    You were right... Full on rollers are on the way.

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    Ok...how bout now?? The lobe lift on this valve is .347. The ratio on the rocker is 1.5 so that should yield .520 on the retainer. I'm actually getting .557. What am I doing wrong? Or is this ok?
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  13. #11
    gn7
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    Is that valve open, mid, or closed?

    Based on the numbers you got with the cast rockers and these, I am beginning to believe that cam is a pinch bigger than they said it is.



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    Quote Originally Posted by Romper Stomper View Post
    Read my original post. It's a Pontiac. Most Pontiacs use 1.5 or 1.65 ratio rockers. I'm using 1.5. Cam lift is .340/.346. I'm sure you can math up the rest...
    Sorry if I sounded insulting. Is this a solid or hydraulic build? I thought maybe it was a pontiac head BBC. Doing the math I have questions about why you are coming up with that much lift? M

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    Quote Originally Posted by gn7 View Post
    Is that valve open, mid, or closed?

    Based on the numbers you got with the cast rockers and these, I am beginning to believe that cam is a pinch bigger than they said it is.
    In the pic it's mid lift. Before I put the heads on, I checked the lobe lift. The cam card says .340 lift and it measured out dead on. Do you think I have the adjustable push rod too long? The rockers I'm using were highly recommended by some Pontiac gurus and the roller is pretty damn close to the center of the valve stem.

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    Quote Originally Posted by ol guy View Post
    Sorry if I sounded insulting. Is this a solid or hydraulic build? I thought maybe it was a pontiac head BBC. Doing the math I have questions about why you are coming up with that much lift? M
    No worries, man. It's a poncho all the way. Hydraulic roller. Doing the math, I have questions about why I'm coming up with that much lift...

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