2quick4u

Smoke,

Anytime you mill your heads on an engine without an adjustable vavletrain like the LS1, it is a good idea to get shorter pushrods or use shims under the rocker studs. This will keep the lifter preload correct and also help keep the valvetrain geometry correct. Just like when you get a smaller base circle cam, it is a good idea to run longer pushrods for the same reason.

Terry Burger

iTrader: (4)

You need to measure the preload and shim as needed to get back to stock levels.

ChrisB

Walter Donnovan from Jesel made a good point on this awhile ago on LS1.com - when you shim the rockers you are increasing the rocker tip -> valve tip angularity. (unless you go with a longer valve - which isn't a bad idea).

Realize this is a 3-point system, and your valve tip height is fixed with relation to the valve seat - so doesn't change when you mill your heads. Your rocker height also doesn't change. The only thing that changes is your pushrod height - so assuming we have optimal valve angularity from the factory you should only change your pushrod length to compensate.

What's the real world difference? it depends on how much you shim - and in reality you wont notice any huge problems. In my mind anyway it's just a matter of "doing it the right way" - and I would go ahead and leave all those heights alone and just spec a proper pushrod.


Chris

blackhawk2000

If the guy who did your valves and seats did the job right, he set them up to the correct specs. If so then you just compensate for the milling, with a shorter PR.

blackhawk2000

Don't forget about the base circle? on the aftermarket cam. If it is smaller, and the heads are milled, then a shorter PR may not be necessary...at least I think that's how it goes <img src="images/icons/smile.gif" border="0">

Dave F

My contacts at GM Racing say to NOT shim the LS series engines. They say that proper torquing of the OEM rockers on the heads is an integral part of re-inforcing the valvetrain.

We run short pushrods in our race engines. I would suggest checking the preload in the OEM valve setup (how many turns past initial resistance in the old adjustable valve sense), then trying several lenggh pushrods until you get the right amount of lifter preload. You could probably gring a stocker down slightly, then order replacements of the final length. This would correct any cam/head changes.

I buy my pushrods from Smith Brothers, and they offer them with oil restrictors which helps keep oil in the bearings, and out of the valve covers.

Dave

[ November 13, 2001: Message edited by: Dave F ]</p>

2quick4u

Dave,

Thanks for the info on the oil restrictor pushrods. I lot of guys who rev their engines past 6,700 regularly could really use these.

Smoke_ur_5.0

iTrader: (2)

Getting the new heads that are milled .025 and someone suggested I may need some .020 thick shims for the rockers since the stock seats were cut down some too to accomodate the 2.02 valves.

What do think? Shims just for a little insurance or is there a good test to see if I even need shims to begin with?

Dave F

ttt

Dave F

Just an fyi: With Lingenfelter CNCd' and shaved heads (don't know how much) and the ASA cam, GM recommends we run 7.265" pushrods with oil restrictors. These are $7.34 each from Smith Brothers (541 388 8188). HOWEVER, upon removing my last motor, 7 of the lifters had lost the retaining clip in the top of the lifter. This implys that my preload was slightly off.

For my next engine/cam, I am going to do the trial and error method I mention above to get the correct length.

Dave