measuring pushrod lengths

[95LT1Z28]

Can anyone tell me how exactly you measure what length pushrods you will need. Like step by step. I guess you need a weaker spring or something if your going to use the pushrod length checker (which I just ordered the comp one from thunder racing)

[mrbadlt1]

x2 i would also like to know the steps

[JAKEJR]

There are several differing ways, all recommended ways, to find the correct length. Depends on which cam company you reference, which mag article you read, which post, etc. So don't expect universal agreement on the procedure since each source seems to have their own version and procedure.

Here's what I do:

I choose the #1 intake rocker, remove the rocker arm and then I install the adjustable pushrod. I mark the valve stem tip with a black magic marker (I use EXPO Bold Color Dry Erase).

I turn the enigine manually until that lifter is on the base circle of the camshaft lobe. I find this by watching what the #1 EXHAUST pushrod is doing.

I install the rocker arm and screw on the poly lock and I eye-ball the rocker roller tip until it apprears to the eye to be centered over the valve stem tip and all slack is removed between the lifter and rocker arm.

I then set 3/4 turn of lifter preload.

I then wiggle the rocker arm tip to remove the marker color from the valve stem tip. Friction will remove a small area of color. I remove the rocker arm and visually check the valve stem tip to see where the color has been removed.

I'm looking for the cleaned area to be slightly in-board (toward the intake manifold) from the center of the valve stem tip. If the mark's not in that position, I adjust the pushrod checker to move the roller tip in the needed direction.

Then I re-mark the valve stem tip with the marker, re-adjust the poly-lock to give me a 3/4 turn preload and wiggle again. I prefer 3/4 turn of preload since it gives me a quieter running valve train. I remove the rocker and see if the mark is now where I want it; if not I adjust the adjustable pushrod again.

Once I get the mark where I want it to be - slightly in-board from the centerline of the valve stem tip - I remove the poly lock, rocker and adjustable pushrod and measure it to find the length I need.

If you don't have a caliper that can measure over 7" in length, just compare the length of the adjustable pushrod with the known length of a pushrod you have laying around, then measure the difference. Place both pushrods side by side with the ends butted against a straight edge, like the back splash on the kitchen counter, etc., and measure the difference between the two rods.

Since after market pushrods are usually offered in .050" increments, without having custom length pushrods made, your measurements don't have to be extremely accurate. If your measurements fall between two different lengths offered by, say Trick Flow, round UP. Better to have pushrods that are a little too long than a little too short.

There are other methods, which involve installing checking springs, cycling the rocker through a complete cycle, etc. etc.

Basically here's what I want the end result to be:

With the lifter on the base circle/heel of the cam lobe, I want the centerline of the rocker's roller tip to be slightly INBOARD of the centerline of the valve stem tip,

then at half valve lift I want the roller tip to be centered over the valve,

then at full valve lift I want the roller tip of the rocker arm to be slight OUTBOARD.

then to return to being CWNTERED over the valve when the valve is half closed and

finally return to being slightly INBOARD with the lifter on the base circle.

Hope this helps.

Jake