I am having trouble measuring the correct length pushrod for my motor.

Car was bought as a cam only car, running TSP's Torquer cam setup, which comes with 7.400 pushrods.

I put thse in my new motor, running a milled .030 head and a .010 decked block. Car is bleeding off compression at higher rpms. When measuring the length of one of my pushrods, it comes out to 7.350. We tried measuring the new length with the car cold but then you have to compensate for lifter preload. Does anyone have any experience in this? I really want to get this car buttoned down soon.

 

i worried drain the oil and spin it to 9000rpm

 

with the heads being milled .030 i would definitely run the 7.350's

 

the prob is that is apparently what is in there and my power curve flattens at/before 6k.

 

The standard answer is “Get a pushrod length checker and determine what length you actually need, not what some people here will guess you need.”

I think I have provided links concerning preload and pushrod length 2 or 3 times in the last month. Search “pushrod length” by date in this forum to find out what I know, which is not much.

ETA
I am not saying the PR length is wrong. I suggest you determine if it is or rule it out. Good luck.

 

This is a post from vettenuts about checking pushrod length. Hope it helps...

Each turn of the pushrod is 0.050". When fully closed, it is 6.800". This is pushrod "gauge length" so you can't measure it directly as the pushrod length is actually based on the length between the ball ends where the ball end measures 0.140" in diameter. Assuming you are using stock rockers or a non-adjustable rocker.

1. Open the adjustable pushrod to the same length as your stock pushrods
2. Close it down two turns
3. Put your rocker rail on the head
4. Make sure you cylinder (typically #1) is at top dead center on the firing stroke so both valves would be closed
5. Put the pushrod in place on the intake valve and make sure it is in the lifter cup
6. Install the rocker and snug down the bolt (don't need to torque, just make sure it is snug)
7. Lift rocker tip up and down, if it "ticks" the pushrod is too short. If you can't easily move the rocker the pushrod is too long.
8. You can try and adjust the pushrod in place but my fingers are too fat so I end up pulling the rocker and adjusting the pushrod length. Go either shorter or longer 1/2 turn and try again.
9. You are trying to get to the point where the lifter doesn't "tick tick" with the pushrod in place nor is the rocker snug. When you get the pushrod length such that you just barely get rid of the "tick tick", you have found "zero lash".
10. When you have found zero lash, carefully remove the rocker and pushrod without rotating the pushrod.
11. Tighten the pushrod until it is fully closed counting the turns as you go.

To figure out your pushrod length you do the following. Let’s assume it took 10-1/2 turns to close the pushrod down to its shortest length after you reached zero lash. Each turn is 0.050".

Your length is then: 6.800" (fully closed length) + 10.5 X 0.050" (number of turns times the length change per turn) = pushrod length minus preload. So for this case:

6.800 +10.5 X 0.050 = 7.325"

This is the length you measured to zero lash without any lifter preload. Now let’s say you want to have 0.075" lifter preload, you add that to the measured number and you end up with 7.400" pushrods.

Now repeat for the exhaust valve to verify the length. If you have something like Yella Terra's, it is the same procedure but you must snug down the rocker pair rather than the single rocker.

 

Forget all the BS about pushrod length checkers etc. They have validity, but are unnecessary. All you need to do with stock rockers is to torque the rocker to zero lash, that's when the push rod stops turning easily when spun between your fingers. Then torque to 22 lb/ft. If torquing takes 1 to 1 1/2 turns you are good to go. More than 1 1/2 turn, needs longer push rod, less than 1 turn needs shorter pushrod.

 

Im running 7.400 pushrods with a torquer 2 cam and heads milled .040. Pretty much equal to what youve got. I calculated it out to be about .011 OVER stock preload. Been running this way for many miles, performs great, no issues. IMO its not the pushrods causing the bleed.

 

My buddy and I had a hard time finding the 'stop' on the PR length checker when we measured on his dry engine. IT was hard to feel.. He found it then we double checked with remeasuring once with each of us.. we both came up with the same measurement. . it takes a FINE touch.. What ever measurement you get, add .050 (or was it .075?) for pre load.. we ended up at 7.350".

We did it w/ the Rockers on.. we had to elect tape the PRLC to keep the damn thing from spinning..

 

I recommend a checker as well. I just put some trans assembly lube on the threads to stiffen up the turns.