Proper push rod length

[Jbrown1238]

I am working on a 306 with GT40P heads, stock valves, Ford Racing lifters, Comp Cam, stock rockers. The block deck surface is OE spec but the heads were decked and the tops of the valve stems were cleaned up a bit. I mocked up my OE push rods to see how close they were. I was hitting my torque spec on several rockers before the push rod felt tension. I could still spin the push rod with little drag even after the torque was set to spec. The lifters are new and they soaked for several days prior to the test. At this point I am sure I need longer push rods but wanted to get a few opinions from forum members here. This is my first build and I want to be sure I am not missing something first.

Both the intake and exhaust valves were closed when I torqued the rockers. What I am finding confusing is that I am still scratching a center patch on the top of each valve stem where I marked it with a Sharpie. Thoughts?

 

[RonD]

Wouldn't make sense for stock push rods to be too short if head was shaved a bit or even just surfaced, they would then be long.

You should be able to spin push rod on closed valve/cam neutral, but not move it up or down.
It means push rod is being pressed down by rocker on to lifter spring enough to prevent play but not enough to cause bottoming, and a floating valve at high RPMs.
So spinning good, play bad

With all rockers torqued, I would manually turn the engine over a couple of full turns then check push rods, that should pump the lifters for a better check.

 

[Jbrown1238]

Wouldn't make sense for stock push rods to be too short if head was shaved a bit or even just surfaced, they would then be long.

You should be able to spin push rod on closed valve/cam neutral, but not move it up or down.
It means push rod is being pressed down by rocker on to lifter spring enough to prevent play but not enough to cause bottoming, and a floating valve at high RPMs.
So spinning good, play bad

With all rockers torqued, I would manually turn the engine over a couple of full turns then check push rods, that should pump the lifters for a better check.

I did spin the engine over two cycles and it did seem to tighten up a bit. But from everything I have read on line I formed the opinion that there should be some tension on the push rods prior to hitting torque at 1/4 turn to 1 full turn without spinning the engine.

 

[Teddyzee]

Priming the engine with a drill is the easy way to pump up the lifters.

Swapping my cam ans roller rockers, I needed longer pushrods. Because they are still pedestal mount, I spent some time with some shims to get the preload exactly as I wanted.

 

[reef93]

I actually just ran into the same issue on my build. Checked the lifter that came out of the explorer motor and compared it to the new Ford Racing lifters we installed and the new ones were actually shorter. Reinstalled the explorer ones and just said screw it. Not sure why they are different but in my case they were.

 

[Jbrown1238]

I actually just ran into the same issue on my build. Checked the lifter that came out of the explorer motor and compared it to the new Ford Racing lifters we installed and the new ones were actually shorter. Reinstalled the explorer ones and just said screw it. Not sure why they are different but in my case they were.

Thank you very much for the reply. I thought of this as a possibility but dismissed it as not likely. I am going to go ahead and compare the new Ford Racing lifters to the OE Explorer lifters and see if they are different in my case as well. I probably would not have done it if you had not posted a reply. Thanks again.

 

[bearsrngr]

The camshaft base circle will also play into push rod length. An after market cam may have a smaller base cirle causing the lifter to ride lower in the bore.

 

[Jbrown1238]

The camshaft base circle will also play into push rod length. An after market cam may have a smaller base cirle causing the lifter to ride lower in the bore.

True, very possible.