zulatr

I changed the cam to a pretty mild Pat G recommended EPS cam and did the heads on my LS7, and have been trying to find my way to the right PR length. Right now I'm short based on the turns to torque method when on the base circle of the cam. I can't use that method to determine the correct length because I'm near zero preload when the rocker torques down.

I bought a PR length checker, thinking it was marked, but it's not, it's just a jack screw in the middle.

My understanding is that PR are not measured end to end, but from a gage diameter on the spherical ends. So if I use the checker, get to a length I want, how do I turn it into PR length?

Arctic 05

You count the turns and multiply them by the thread pitch. They should tell you the pitch and the pushrod length at zero turns.

zulatr

The one I got from comp cams, PN 7901-1, isn't marked in turns, it's just double nutted.

xBoostx

If you only change the cam and did not milled the heads your push rod length should not have change, if you want to know the lash to push rod binding, install a rocker arm and tight it down as usual then with the valve in close position use a leverage arm of some kind to push down the rocker with a dial indicator on top of the rocker arm tip just above the valve stem to see how mush the rocker travel till binding.

If you have 0.020 or more you are good.

The length is measure from tip to tip or overall length.

I use a 12" dial caliper to correctly measure push rod length.

An adjustable push rod is best used in conjunction with a soft spring sold for this purpose although is not necessary if you can get a leverage arm some how made for this purpose.

zulatr

for the length checkers that are not marked in turns or with a specific beginning length, like the one I have, Comp Cams technical line said take .033" off the overall length.

Guess I'll give that a try, not feeling great about it though.
Anyone else?

2k Cobra

Question from one who doesn't know....

If the new cam has a different base circle than the OEM, wouldn't that require a different PR length??

TIA

xBoostx

So a pretty mild cam from Pat G- and what in wonderland is the real chance of an altered base circle on a mild cam?

Ah by the way the lifters don't ride on the base circle but on the cam lobes and these cam lobes are design to replace ls engine cam with ls cam lobes characteristics, so yeah it should be the correct base circle.

zulatr

lifters run on the whole cam profile. If they "jumped" over the base circle the impact would beat them to death in no time.

I am very clear that I need to make pushrod measurements on the base circle. Measuring on TDC may work for some cams but will not work for others, including mine, which measured different at TDC than at the EO/IC method.

zulatr

Yes, I've learned that you can put the same pushrod in on most cams and they will work, though you may end up on here discussing valve train noise, or may luck out.

Wisdom is that if you change the cam, lifters, have your valves reseated (read this everyone who has had their guides done), or milled the heads, you should check PR length.

In my case I had the guides redone, which requires the valves to be reseated and sinks them into the head, the head was then milled to adjust the chamber volume, and of course I have a new cam.

Speedforhire

I use the old-school, felt marker method.......tedious, but very effective.