[indymanjoe]

As a virgin to this stuff i found this vid and wondered if it applies to our Pontiacs? still researching correct valve train geometry.

https://www.youtube.com/watch?v=RjaosX63DkM

[steve25]

Why would it not apply to Pontiacs?
I did not watch the video, but our Pontiacs have rocker arm, push Rods and lifters right?

[indymanjoe]

i dont know alot about this stuff but i am trying to learn all i can about it.

[Holeshot71]

Interesting video.. So basically what he’s saying is that if you’re running stamped steel rockers there really isn’t any need to worry about the contact pattern at the tip of the valve.

[steve25]

What is not mentioned then is even though the contact pattern is wider with a stamped steel rocker of the type used in Pontiac’s there is still the loading and ware factor that can be tweaked.

It’s super that you want to learn but no amount of video watching takes the place of fooling around with a adjustable push rod to see the effects.

If your reusing stock rockers he sure to take the time to look at each push rod ball socket for even ware before you go checking geometry.

[Skip Fix]

Back in Pete McCarthy's old magazine he had an article on it for a Pontiac. Yes you can measure it. My theory is since the rocker is hitting the valve tip in a different area the actual real lever arm length changes.

[tooski]

I've seen that vid, too. Apparently not concerned with geometry, just increasing lift.

[ANDYA]

Years ago when I put together my 428 I measured for correct push rod length. The cam was speced at .520 lift with 1.5 rockers. I put a dial indicator on the spring retainer to check for max lift. Only when I got the correct pushrod length was I able to get the correct lift of .520. If I made my adjustable pushrod shorter or longer I could not get the correct lift. It would always be less lift. The only way I was going to get a higher lift was to use higher lift rockers. I’m putting together a 455 right now. Next week I will be playing with pushrod length and rocker geometry again. This will be with an 068 cam and 1.65 rockers. Should be interesting what will happen this time.

[steve25]

With stock rockers just note that unless you go thru 5 to 6 sets of them to get the most accurate ones they will average 1.45 to 1.48 in ratio.

[Schurkey]

Originally Posted by steve25

Why would it not apply to Pontiacs?
I did not watch the video, but our Pontiacs have rocker arm, push Rods and lifters right?

Any engine with non-adjustable rockers does not change geometry with pushrod length. Pushrod length changes affect lifter plunger preload only.

Pontiac with "bottleneck" studs and nuts torqued to 20 ft/lbs aren't going to benefit from changes to pushrod length as long as the length is reasonable--applies some preload, but not too much.

Engines with adjustable rockers--including those with shims under pedestals--MIGHT benefit from pushrod length changes. The amount of lift may change, and the sweep across the valve tip may change.

Excess sweep across the valve tip wastes rocker-motion and tends to wear the valve guides from the side-thrust.

I would expect--but have not personally verified--that minimum sweep and maximum lift occur with the same, "correct" pushrod length.

[skunkwerks]

Push rod length is checked whenever you deck the block and heads change the cam and rockers or all of the above. You want the valve tip to be centered on the lift profile so that it evenly distributes the side loading and pressure. This will keep your valve guides from abnormal wear and valve stems from getting mushroomed. Plus you will have less valve float at higher RPMs.
Always get a push rod length checker. Comp has a good tutorial. Then order the correct length. Your engine will thank you.