Just installed new cam and using my 7.40 push rods that I had previously for measurement.


This is what I did;

- Rotated engine and observed exhaust valve opening. This puts intake on base circle.
Tightened intake rocker to 0 lash. Then set torque wench to 22 foot pounds and began to tighten. I was only able to get approximately 1/4 of a turn before reaching 22 foot pounds.

- Rotated engine and observed intake valve closing. This puts exh on base circle. Repeated zero lash and torqued to 22 foot pounds as above and also came up with 1/4 turn from zero lash to 22 foot pounds.

Each turn of the rockers bolts = ~.047" and I am running LS7 lifters.

Shooting for ~.070" pre-load, I am only getting ~.012 (1/4 turn) with these 7.40 push rods.

Based on the above, I think I need a 7.45" push rod to get my pre-load where I want...?

Heads were only surfaced and block has been milled.

 

I would recommend getting a pushrod length checker, thats the only way to know for sure what you need.

 

I didn't come up with the aforementioned method in a vacuum...

 

Maybe I mis-read, but it sounded like you were using your old 7.4" pushrods and counting turns when tightening the rocker arm blots down?

I was suggesting an adjustable length checker (i.e. COMPs tool).

Maybe I just don't understand your method, when I was putting my engine together I had the intake valve closed and on the base circle like you are describing, then installed COMPs tool and snugged down the rocker arm, adjusted up to zero lash, then counted the turns on the tool (one turn = .050") and added my desired amount for pre-load (.075 pre-laod with 7.325 rods in my case).

This method seems the most accurate to me, multiple ways to skin a cat, just trying to help.

 

Ok i went though my book again (Joseph Potak) and found the PR section, he mentions a second method using known length rods and a dial indicator.

He does what you did in step one to get to zero lash on base circle, then zeroes out the dial indicator then tightens the rocker arm until its bolt is bottomed out and the rocker is tight, he doesn't mention using a torque wrench in the process, don't know if that could throw your measurement off or not.

 

Ok, after you get your length with the checker,and get the proper length pushrods, how do you compensate for whatever pre-load you get torqueing the bolt to 22ft lbs? Whenever you torque the bolts, they are going to put more pre-load..........or am I missing something?

 

The turn method **** might be the worse thing to have come about in the ls world. It is not accurate, even if some claim it has been succesfull. Stock lifters are relatively forgiving, so ballpark is usually close enough for that crap to work.

Watching the valves like you did only works if your cam has exactly 0 overlap.

Buy the pushrod checker.

 

You don't need to compensate for that, once you get the proper length with the tool and add for your desired pre-load, that's what it will be.

 

i wish whoever invented the "measure pushrod preload by rocker bolt turns" method would choke on a D and die. get a pushrod length checker and measure. every other method is a guess.

 

^^ THIS

The bolt turn method ignores that the fulcrum of the rocker arm is moving during the measurement. The rocker ratio throws off the measurement. So xx" inches of bolt turn is NOT xx inches of pushrod length.

Doesn't work. Never will. Buy the pushrod checker.