Checking Pushrod Length

duo_z · Aug 24, 2011

I have been reading how-to's on checking pushrod length and I just want to double check things.

I have hydraulic lifters in my car. I can't check length with them because they are flat. So I have to get a solid lifter to take its place while checking. How am I sure that the solid lifter will be the same as the hydraulic?

Once past that step and getting the lifter in, I set the pushrod length so that its movement on the valve stem is in the middle. Correct? Is there anything I am missing?

SitDown · Aug 25, 2011

I used the adj TFS rod and a washer stacked stock hyd lifter. Sharpie marker up the valvestem tip and give it a few revolutions to confirm your center.

mtaqua · Aug 26, 2011

The reason you use solid lifters is the to ensure your lifter is the same length as it would be when the car is running. The Hyd lifter uses engine oil when running and is a different length than when it was no fluid in it.

I originally bought the TFS checker, and then bought the more expensive comp check. It allows you to determine measurement based on the number of times you unscrew the top. Much easier, and it seems to be a more solid tool.

When measuring the push-rod length, center of the valve tip is not necessarily what you are looking for, but that is ideal. You want the shortest sweep on the valve tip. So use the sharpie to mark the tip; rotate the roller tip with the valve closed, then mid lift then max lift (or just roll the motor over several times); use weaker springs or you might bend the push rod checker tool. This should make a band on the top of the valve. Increase/decrease the push rod length until the band is as narrow as possible. When the band is narrow as possible the rocker tip and valve tip are as close to 90 degrees as possible and you reduce side loads on the valve (reducing valve guide wear). If the narrowest strip possible is to far off the valve tip center then you might need to change rockers (or something else to change the geometry; lash caps shorter/longer valves).

duo_z · Aug 27, 2011

So a solid lifter will have the same geometry as a pumped hydraulic lifter? I have a comp cams checking tool. What type of sprigs would you recommend for checking it and where would I get them?

mtaqua · Aug 27, 2011

I believe a standard SBF solid lifter should have the same over all length as a standard SBF hyd lifter that has fluid in it. I'd call the manufacture of who ever made your lifters and ask them which solid lifter they recommend for checking push rod length. Maybe some here can help on that, I had solid rollers on mine.

Proform Parts 66793 - Proform Valve Check Springs - Overview - SummitRacing.com I used the springs that came with my degree kit. The only down side is the low tension springs don't push on the rocker tips to much so it can be a challenge to get a proper marking on the valve tip. I was told to removing my inner spring would be enough to keep the tool from bending.

mycoses · Aug 30, 2011

I disagree with using solid lifters or weak springs to check rocker arm to valve tip relationship. Hydraulic cams run with the lifters under a 'preload' from the PR. That is the stock geometry set up. Solid lifters change that preload set up and are only good for testing mechanical cams. Weak springs also change the rocker arm to valve spring relationship. The set up prior to testing should be as close to a running motor as possible. ie. assembled valve train, preload on the lifters,normal springs. Attach the head with the usual head gasket(use an old gasket so you don't crush the new gasket too much. )
mark the valve tips. Attach the rockers and PR for one cylinder. Set the preload on the lifters. Turn the motor over by hand a couple of times and take off the rockers to see the pattern on the valve tip. Should be centered on the valve tip. If not then increase or decrease the length until centered. The width of the wear pattern is controlled by the geometry of the valve train and should not be a concern as long as the wear is centered. Just triple check you have all the correct parts. For example, the wrong lifters would probably be a different length than stock and would change the geometry significantly. Let the discussion continue.

PoppyMod · Aug 30, 2011

duo_z said:
I have been reading how-to's on checking pushrod length and I just want to double check things.

I have hydraulic lifters in my car. I can't check length with them because they are flat. So I have to get a solid lifter to take its place while checking. How am I sure that the solid lifter will be the same as the hydraulic?

Once past that step and getting the lifter in, I set the pushrod length so that its movement on the valve stem is in the middle. Correct? Is there anything I am missing?

Hi,
I'm running a very successful build, that I assembled myself. I used checking springs, adjustable P/Rs with the lifters (link bar hydraulics) I was going to run. I've followed the recommendations of having a centered pattern with a width of about .070. This worked for me. It is important to check both intake and exhaust. My heads have 7/16 X 20 studs and am running a 1.6 ratio CompGold rollers. With this combination, I needed just over a 1/4 turn to make my pre-load goal within the range of .020 to .060.
This worked for me. In the end, I wound up with 6.750 P/Rs.
Good Luck!

mtaqua · Aug 30, 2011

All I've done are with solids, after re-reading some of my "sources" you should make the hyd lifter solid. Like Sitdown did. There are some post on the bottom that talk about this.

As far as weaker springs (or checker springs), I don't think a weaker spring is going to change the geometry from a static point. The cam will push on the push rod to the rocker to the valve. I can see while in motion with flex (operational RPMs), and other things occurring how the geometry could change, slightly. The problem with not checking with a weaker spring is you could very well bend the checker pushrod, and your measurement will be off. Ideally, I'd check them the springs you are running, but I bent my first tool doing this.

Centered on the valve with the narrowest band possible is ideal. I'd take an offset narrower band over a wide centered band. I saw this on the corral post below, and then in a couple other post. I thought about it, and from the dynamic loads produced from the rocker going back and forth on the tip I believe the loads on the guides will be higher than a slightly off centered, but 90 degree valve to rocker relationship. While the roller rocker tip will reduce friction, and allow the tip to rake back and forth, this will produce side loads on the valve (which will affect guide wear). I am sure the guide will provide some support to a slightly off centered load. I have not done any math to try to compare the loads, but I can't see the off centered load being greater than a constant side to side load. I am sure there is a limit to how far off center is acceptable, but I am not sure what that would be.

I am not an engine builder, and do not claim to have all the answers. Heck my sources are from folks on the internet who I've never met. I am just trying to look at it from an engineering stand point, so I could be way off.

http://*******.com/index.php/topic,317.0.html
Pushrod length - Yellow Bullet Forums
Bad info floating around about measuring Pushrod length - Ford Mustang Forums : Corral.net Mustang Forum

PoppyMod · Aug 30, 2011

mtaqua said:
All I've done are with solids, after re-reading some of my "sources" you should make the hyd lifter solid. Like Sitdown did. There are some post on the bottom that talk about this.

As far as weaker springs (or checker springs), I don't think a weaker spring is going to change the geometry from a static point. The cam will push on the push rod to the rocker to the valve. I can see while in motion with flex (operational RPMs), and other things occurring how the geometry could change, slightly. The problem with not checking with a weaker spring is you could very well bend the checker pushrod, and your measurement will be off. Ideally, I'd check them the springs you are running, but I bent my first tool doing this.

Centered on the valve with the narrowest band possible is ideal. I'd take an offset narrower band over a wide centered band. I saw this on the corral post below, and then in a couple other post. I thought about it, and from the dynamic loads produced from the rocker going back and forth on the tip I believe the loads on the guides will be higher than a slightly off centered, but 90 degree valve to rocker relationship. While the roller rocker tip will reduce friction, and allow the tip to rake back and forth, this will produce side loads on the valve (which will affect guide wear). I am sure the guide will provide some support to a slightly off centered load. I have not done any math to try to compare the loads, but I can't see the off centered load being greater than a constant side to side load. I am sure there is a limit to how far off center is acceptable, but I am not sure what that would be.

I am not an engine builder, and do not claim to have all the answers. Heck my sources are from folks on the internet who I've never met. I am just trying to look at it from an engineering stand point, so I could be way off.

http://*******.com/index.php/topic,317.0.html
Pushrod length - Yellow Bullet Forums
Bad info floating around about measuring Pushrod length - Ford Mustang Forums : Corral.net Mustang Forum

Hi,
I don't claim to be any kind of a great builder, only that I've managed to survived the rigors of road racing where endurance is key, not straight line flash. What you bring to the table is a re-enforcement of how important it is, and how intricate this often over looked, yet important aspect of engine building is, to valve train technology and enduring reliability.
It's just another part of the blue printing trail.
Happy Motoring!

Checking Pushrod Length

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