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Old 09-11-2019, 08:45 PM
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Stripes Stripes is offline
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Default Pontiac Pushrod length, valve train geometry

In our 455 Pontiac equipped with: new E d port heads, a butler/comp hyd roller, .060 cosmetic head gaskets, comp cams hyd roller lifters and scorpion endurance roller rockers. With 1/2 turn of lash past zero lash, the "track" is perfectly centered on the valve stem, showing a needed pushrod length of 9.15" (with my comp cams 7704 pushrod checker tool). The block was decked below zero, thus the need for the thicker head gaskets.

My concern is the cam/lifter supplier indicated a likely pushrod length of 8.8 to 8.9", so mine seem too long. I was told track location was unimportant, only having a T or 90-degree angle at 1/2 lift was important to set valvetrain geometry. I cant see 0.10 by eye to know if its square or not. I've measured with check springs and an adjustable pushrod and also a comp mag pushrod (9.13") w real springs and have the same results.

I attached 3 photos. One shows the geometry at 1/2 intake lift on cam with a 9.13" pushrod, the other shows the track with a 9.13" pushrod. It looks good to me.

I tested 8.80" up every .050" to get to this 9.15". The shorter pushrods definitely had the track at the intake side of the valve stem as seen in the third photo.

These lifters have not been run in an engine yet. I adjusted them to zero lash and added 1/2 a turn.

Does the pushrod length look right to you?
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Last edited by Stripes; 09-11-2019 at 08:59 PM.
  #2  
Old 09-11-2019, 09:02 PM
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gtofreek gtofreek is offline
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I have a hard time seeing the rollout pattern on the valve tip. It needs to be as narrow as possible. Centered is nice, but not necessarily correct geometry. Longer valves than stock will move the correct geometry off center because the valve tip gets closer to the rocker stud. I just built a stroker engine with a roller cam and Hylift/Johnson roller lifters. That engine took a pushrod length of 8.950". That engine had the Edelbrock D-ports, and Scorpion rockers also, just like yours. Shoot for the narrowest rollout pattern you can get. That should be around .060"-.070" wide at the most. If you are around .100", your geometry is off because the rocker is rolling across the valve tip which you don't want. Narrow means the rocker is pushing down in pretty much the same spot throughout the lift curve.

Also, make sure your lifter is not collapsing. I have seen some lifters collapse even with a tester spring. The one in your picture will definitely be depressing the lifter plunger with the real spring on there so you can't go by how that one looks.

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  #3  
Old 09-12-2019, 04:59 AM
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If you are using hydraulic lifters do all the checking with the plungers bottomed out in the lifters. With new parts they should collapse very easily, if not just push all the oil out of them, typically takes less than 120 seconds to accomplish this.

Once you have them completely bottomed out mark the valve and keep adjusting the pushrod to establish the narrowest pattern (hopefully pretty well centered) as Paul mentioned.

I usually check one intake and one exhaust assuming the heads have all the valves at the same height in them.

Once you have established the best pattern check the pushrod length and subtract the amount of running rood that you want. I prefer to run mine much closer to the plungers bottomed out than down a little from zero lash. These lifters have a bad habit of making excessive noise if you run them with too much oil under the plungers.

Also check the available travel of the plungers. In recent years the manufacturers have been making changes to the designs and shortening up the travel some. I've found it is better to run HR's tight lashed or plungers deep in the lifters vs going to zero lash and down 1/4 to 1/2 a turn (often accepted "standard" for adjusting hydraulic lifters).

I used Scorpion rockers arms once and after apprx 4 years 14 out of 16 of them were cracked as shown below. Not a big fan of most of the roller rockers that are out there and these days I stick to Crower Enduro's if/when we get involved with one of these engines.......Cliff
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Old 09-12-2019, 08:55 AM
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Posted this in the other thread, at least look at the approach, it's easy, and accurate.

https://www.youtube.com/watch?v=o5is9BsH5OU

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Old 09-12-2019, 12:55 PM
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Thanks, Cliff. I need your new book "All the Pontiac Parts That Didn't Last Or Work!"
Seriously, it would sell.

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Old 09-19-2019, 11:54 PM
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I rechecked using the examples provided and came up with 8.85". Appears the track in the center of the valve stem is bs. It's the 90 degree angle at mid lift that counts! Thanks for all the help!

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Old 09-20-2019, 07:29 AM
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Quote:
Originally Posted by Stripes View Post
I rechecked using the examples provided and came up with 8.85". Appears the track in the center of the valve stem is bs. It's the 90 degree angle at mid lift that counts! Thanks for all the help!
Correct.


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Old 09-20-2019, 10:22 AM
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Quote:
Originally Posted by Stripes View Post
Thanks, Cliff. I need your new book "All the Pontiac Parts That Didn't Last Or Work!"
Seriously, it would sell.
Most of the "Pontiac Parts" are good in the right application..its the aftermarket stuff to be aware of..
Top of Cliff's list would be "Mutha Thumping Cams", E Carbs and those cheap cast roller rockers.

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  #9  
Old 09-20-2019, 10:39 AM
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I would add to the list:
Edelbrock Performer intake
Aftermarket valve covers that dont fit under the brake booster
Water wetter radiator fluid additive
High flow thermostats
Certain Flex fans
Certain aftermarket water pumps that claim 15 degree drop

  #10  
Old 01-24-2020, 12:28 AM
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Bringing to top, good info

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