Pushrod Length, best method

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BigBlocksOnTop2
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Pushrod Length, best method

Postby BigBlocksOnTop2 » Sat Nov 08, 2014 7:21 am

Checking for pushrod length down in the engine bay of a 69 Mach 1 is no easy thing. Looking at the Manton site on determining pushrod length, ''a light turned on'' and this is to me the best method. I put a piece of masking tape on the side of the rocker. Drew a fine line on the tape that intersected the centers of the roller tip and the trunion axles ( you can see the machine marks so the centers are pronounced).Installed, set up dial indicator and opened valve to half lift. Now, heres the trick.I used a piece of 3/16'' square high speed steel, layed it on top of the retainer and let the piece lay beside the rocker. Now I made adjustments to pushrod length until the drawn line on the masking tape and the high speed steel bar are parellel.

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Re: Pushrod Length, best method

Postby bigfoot584 » Sat Nov 08, 2014 9:05 am

That's slick should work well, assuming your also keep the valve at mid lift
that would change as you very the pushrod length.

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Re: Pushrod Length, best method

Postby lorax » Sat Nov 08, 2014 9:31 am

I have been using key stock across the retainer for years. Not exactly sure why its necessary to use high speed steel.

There is an easier way that does even require a dial indictor except to check your work once you have determined the PR length.
cstraub made a video explaining the easiest method I've seen yet, and it works. I will warn you that its makes no account for valve lash, but that is easy enough to allow for if you want the PR length perfect.

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

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Re: Pushrod Length, best method

Postby BigBlocksOnTop2 » Sat Nov 08, 2014 9:45 am

lorax wrote:I have been using key stock across the retainer for years. Not exactly sure why its necessary to use high speed steel.

There is an easier way that does even require a dial indictor except to check your work once you have determined the PR length.
cstraub made a video explaining the easiest method I've seen yet, and it works. I will warn you that its makes no account for valve lash, but that is easy enough to allow for if you want the PR length perfect.

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


The reason for the high speed steel was readily available

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Re: Pushrod Length, best method

Postby PackardV8 » Sat Nov 08, 2014 9:58 am

Only slightly off-topic, but how often do you find yourself having to choose between the perfect mid-lift pushrod length and the one which gives the most-centered stem tip wipe pattern?
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Re: Pushrod Length, best method

Postby lorax » Sat Nov 08, 2014 10:01 am

BigBlocksOnTop2 wrote:
lorax wrote:I have been using key stock across the retainer for years. Not exactly sure why its necessary to use high speed steel.

There is an easier way that does even require a dial indictor except to check your work once you have determined the PR length.
cstraub made a video explaining the easiest method I've seen yet, and it works. I will warn you that its makes no account for valve lash, but that is easy enough to allow for if you want the PR length perfect.

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


The reason for the high speed steel was readily available

Oh, I was ready to throw out my key stock for new stuff. :D
Last edited by lorax on Sat Nov 08, 2014 10:08 am, edited 1 time in total.

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Re: Pushrod Length, best method

Postby lorax » Sat Nov 08, 2014 10:02 am

PackardV8 wrote:Only slightly off-topic, but how often do you find yourself having to choose between the perfect mid-lift pushrod length and the one which gives the most-centered stem tip wipe pattern?

I really don't much care where the swipe is, so long as its on the valve.

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Re: Pushrod Length, best method

Postby BigBlocksOnTop2 » Sat Nov 08, 2014 10:12 am

bigfoot584 wrote:That's slick should work well, assuming your also keep the valve at mid lift
that would change as you very the pushrod length.


I should have worded differently. It took me two set-ups to get it right, removing the pushrod and adjusting each time. Waiting on my delivery from Manton.
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Re: Pushrod Length, best method

Postby MadBill » Sat Nov 08, 2014 11:22 pm

lorax wrote:I have been using key stock across the retainer for years. Not exactly sure why its necessary to use high speed steel.

There is an easier way that does even require a dial indictor except to check your work once you have determined the PR length.
cstraub made a video explaining the easiest method I've seen yet, and it works. I will warn you that its makes no account for valve lash, but that is easy enough to allow for if you want the PR length perfect.

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


FWIW, the Straub method also results in minimum sweep.
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Re: Pushrod Length, best method

Postby PackardV8 » Sun Nov 09, 2014 12:35 am

Very well done video.

For those of us with shaft-mounted rocker arms, it's a much more cumbersome process.

Don't I remember Miller's mid-lift treatise mentioning a right angle to the pushrod being involved also?
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Re: Pushrod Length, best method

Postby Adger Smith » Sun Nov 09, 2014 2:27 am

Think about it...It is all about the Arc the roller tip swings. The center of the arc is at half lift. I always use "Net Lift" instead of gross lift even though the rocker is moving through the arc when it is taking up lash.(non valve movement) I feel that allows for any deflection issues.
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Re: Pushrod Length, best method

Postby lorax » Sun Nov 09, 2014 8:32 am

PackardV8 wrote:Very well done video.

For those of us with shaft-mounted rocker arms, it's a much more cumbersome process.

Don't I remember Miller's mid-lift treatise mentioning a right angle to the pushrod being involved also?

That's getting into "design geometry" as opposed to installed geometry.
For the pushrod side to correct also would require a specific rocker designed for each engine, and in some cases each valve such as the BBC intake and exhaust.
You look at the 385 and 335 Fords, and they use the same rocker, but the attack angle of the pushrod are very different.
Installed mid=lift as we use it is "free". Design geometry is far from it.

MadBill wrote:FWIW, the Straub method also results in minimum sweep.


I've never seen a case where mid lift didn't result in the narrowest sweep. Its trying to fight WHERE the sweep falls on the valve stem that results in a wider sweep. Lots cases where mid lift is not going to land the sweep in the center of the valve stem where many think it has to be that results in a wider sweep.

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Re: Pushrod Length, best method

Postby BigBlocksOnTop2 » Sun Nov 09, 2014 8:51 am

I'll share my set-up. It's a .563 lift solid mech., Scorpion 1.6 and a 8.55 length push rod. It's a 351 Windsor 9.5, .040 gsk. and unmilled Canfield heads. The contact patch is about .050-.055 wide and is just inboard of center (just enough to say ''just inboard'').

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Re: Pushrod Length, best method

Postby wyrmrider » Sun Nov 09, 2014 10:04 am

When using longer valves, in for example, a SBC the valve stem tip moves closer to the fulcrum
I've relocated the studs, used shorter arms, used backset fulcrums etc to get the fulcrum at the proper distance AND height (easier with studs) for proper geometry and therefore minimum contact patch
You need to get the trunnion at the right height by setting the valve at half lift and taking a line across the tip towards the trunnion (perpendicular to the stem and then locking the trunnion in place, putting a small spring under the rocker body works, then you can measure for pushrod
the pushrod length changes with tip height and with cam lift
Packard - if you are running off the edge of the tip you have to change something or lash caps
But it really does not matter much where the pattern is, trying to get the pattern in the center by changing fulcrum height and pushrod length will get you all screwed up
Now to watch the video

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Re: Pushrod Length, best method

Postby Nick Campagna » Mon Nov 10, 2014 7:18 am

Mid lift makes a lot of sense, on both sides of the rocker arm. One of the problems with stud mounted rocker arms, is the the stud and the valve are not parallel. When the rocker is run up and down on the stud, the geometry and sweep will change. For a given cam lobe net mid lift, 90 degrees to the valve should also be 90 degrees to the push rod for max effect. The rocker needs to have the proper trunnion to tip length, and trunnion to push rod cup length, with the right angle between the two lines. An adjustable push rod cup (for depth) could go a long way towards maximizing lift all around. That's my opinion and I'm sticking with it for now.
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