VandykeT/A

On my car im running a set of 7.450 rods. I didn't exactly go about measuring the right way and ended up just puttin these in. With #1 piston at top dead center. Both valves closed. I can take both rockers with just the slightest resistance and move them side to side and hear a click click. It seems as if they're perfect to me but i need you guys opinion. I have a little bit more valvetrain noise on cold start and it got me scared. My way of choosing rods before was just gettin what other people ended up with for the same combo it was dumb i know.

z99ls1

iTrader: (12)

Are your heads milled? how did u measure for pr length?

VandykeT/A

I've got a checker but i had a friend do the install and he kept getting shorter rods tahn stock so i just got online and looked for what other people with the same set up used. Its PRC 215s milled to 60cc.

ZeeOSix

The best way to determine required pushrod length is to know the total plunger travel of your lifters, and to then use a pushrod length tool to get the distance from the rocker arm to the lifter without compressing it. Ad half the distance of the lifter travel to the distance you have found with the length checker and that will be the pushrod length that will put your lifter at mid-point when the valves are closed.

crainholio

iTrader: (2)

How many times will you be posting this problem? Just a few days ago it was this:


Measure your preload either with a tool or by using Shane's rocker bolt method.

djfury05

iTrader: (30)

Either get checking springs and a valve spring removing tool or take the heads off and use 2 solid lifters to check the pushrod length. You can get a close estimate with the hydrualic lifters and valve springs installed but you really have to ensure the plunger does not get compressed and when you are talking .050 difference to the eye then you are chancing it. Stupid idea to just throw in pushrods without measuring.

vettenuts

iTrader: (4)

Piston at TDC the rockers will easily move side to side. It has no bearing on the preload value. If you have the piston at TDC, back off on the intake rocker bolt until it is loose. Wait a few minutes to ensure the lifter plunger is up, then gently tighten the bolt between your fingers and gently lift the rocker tip until the "tick" "tick" just disappears. Don't lift hard as you will depress the lifter plunger. That will be zero lash. Now count turns to 22 lb-ft and see what you get. You want about 1-1/3 turns or so.

crainholio

iTrader: (2)

Adding to vettenuts' post, here is Shane's version that I found useful until I bought a length checker:

vettenuts

iTrader: (4)

If you need to buy new ones, best to measure but the count turning will at least give you an idea of where you are with the current setup. From there you can make decisions on what to do next.

z99ls1

iTrader: (12)

So i culd put my stock pr's in with my new cam and if it takes more turns tell 22 ft lbs than u need a bigger pushrod correct?

vettenuts

iTrader: (4)

The stock ones are 0.065" shorter. I would first just count turns with the pushrod that is installed and sort out what to do from there. Right now, you don't know where you stand and everything else is a guess.

z99ls1

iTrader: (12)

Ok but here is my thinking.. The only reason you need different length pr's is because of the smaller base circle on the cam right? So why not just measure the stock cam and the new cam and if the base circle of the new cam is .025 smaller than the stock cam, than you put in .025 bigher pr's right?

crainholio

iTrader: (2)

In theory that's basically right, except you want the radius of the base circle (* 0.5).

Reality is another story. If a person won't pay $20 for a pushrod checker, what's the chance of him popping for a decent micrometer?

z99ls1

iTrader: (12)

Seems to me it wuld b easier to measure the lobes with a micrometer and it wuld be exact.

VandykeT/A

I've got a pushrod length checker I've just all ready got it together and from pulling the cover I seen this and i didn't know if that was a way of telling if they were close to being correct length or not. The reason i just ordered a set based off other people was because he wasn't sure how to measure. When he measured i ended up with a shorter than stock rod and everyone else ended up longer so i knew it wasn't right. I know when using the pushrod length checker (comp cams) every turn is .050. But all this about zero lash and preload and base circle just confuses the hell out of me. With the checker what do i need to do to check it properly.

ls1 1990 VN

Find a mechanic!!!

z99ls1

iTrader: (12)

Im not 100%, but I think you set your pr length checker to the number of what you think you need for a pushrod size. Like 7.4 is probably a good starting point. Than you put it in, put your rocker on and tighten your rocker arm down tell you get to zero lash(when you can't hear the click, click noise between your pr and your rocker). Than you set your torque wrench to 22ft lbs and tighten it tell you reach 22. It should take you about 1 and 1/4 turn to reach 22 ft lbs with the right length pr I beleive

z99ls1

iTrader: (12)

Originally Posted by XtraCajunSS:

1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.

For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...

I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.

If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.

THIS METHOD ALWAYS WORKS!!!

I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!

Shane.................................................. .................................................. .............................................

The only thing I don't get about the info above is the part where he says if you have a 7.400" pushrod and you get 3/4 turn that you would need a .025" longer pushrod??? If you reached your torque spec in less turns that you should have wouldn't you need a shorter pushrod?

VandykeT/A

ha ha the find a mechanic is good advice. I all ready have actually, the problem is im afraid to drive the car the 4 hours to them.

ZeeOSix

As others pointed out, finding the difference in cam base circle radius and adjusting the pushrod length accordingly would work. BUT, only if the pushrod was setup correctly in the first place on the original cam.

In this case, it sounds like the that was never done correctly, so seems the pushrod length for the new setup just needs to be determined with a pushrod length checker from scratch to do it correctly.