Vertigo

iTrader: (1)

Guys I've got a pretty tough one here. This will be hard to explain but I'll do my best.

I just installed comp OE-R lifters and stock rockers on my newly cammed GTP.
My question concerns preloading them to 0 to 1/8th turn. 0 would indicate no vertical movement out of the pushrod. Well the issue is this....

Once I get no vertical movement out of the pushrod and can still rotate it as should be the round bottom portion of the rocker (up top) is not fully seated in the pedistul...allowing the pedistul to move around underneith the rockers. In addition the bolts on the rockers seem very loose. So loose in fact that if I were to push down on the rocker to seat it all the way down of the pedistul a space opens up between the top of the rocker and the rocker head stud making me wonder if I should thread it in 1 to 2 more threads that my pushing down gap has created.

Now to even complicate matter more, I noticed that the lifters (bottom) give a little spring action even after I have no more vertical movement from the pushrods. In other words once I tighten the rocker bolt enough to take up all pushrod slack (I still have a loose rocker bolt and a loose pedistul) I can use the rocker to push down on the pushrod causing the pushrod bottom to push in the lifter spring plate.

So my question is just exactly how/when should i add that 1/8th preload turn?

Do I take up all slack in the rocker stud and make the fit between the pedistul and the rocker tight then add an additional 1/8 turn? I don't think so b/c what does that buy me? All space is already taken up.

Or

Do I reach 0 preload by leaving the gap up top and making sure the lifter spring plate is all the way up top and then add that 1/8turn (which by the way will still leave the pedistul loose under the rockers and leave the rocker stud/bolt pretty damn loose?

I can take pictures/video if need be to clarify. Just ask.

Thanks a million!

Wnts2Go10O

iTrader: (12)

first question:
did you soak the lifters in oil before installing?

second, u tighten until the rocker hits resistance from the lifter. do not tighten it and bottom out the plunger in the lifter. after you take out the slack, you do your preload, let it bleed down, then off you go.

XtraCajunSS

iTrader: (2)

Sounds like you have the incorrect length pushrod for your application. You MUST use the proper length pushrod with a "net-lash" rocker system. Unless you convert to adjustable rockers, you will need to find the proper pushrod length first. This method below should work for you, you can ignore the first paragraph dealing with LS specific engines... Also, soaking the lifters in oil will have NO effect on preload or pushrod length measurment, the plunger spring will hold the pushrod cup up.

FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.

Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.

I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.

Here it is again in a nutshell:

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!!!

Check it using the above method and see where you are.

Thanks,
Shane