Lifter Preload, now what?

Ok, just checked the lifter preload for the new cam. I am using a 7.200" pushrod from an 89 305 chevy roller cam. I put the lifter on the base circle of the intake lobe, and torqued the rocker arm down. I left the lifter bleed down and i made a mark on the pushrod, using the head(valve cover mating surface) as a level surface to scribe a line. Then i made another mark after the lifter had no load on it. I measured the distance between the two marks and its about .070". Did i do this proceedure correct? I'm going to call comp tommorrow and see if i can get a pushrod that would give me the recommended preload of about .040". So does this mean that i need a 7.150"- 7.170" pushrod???

You use pedistal shims to get the proper preload unless it throws your rocker arm geometry off, if shiming throws the geometry off you need shorter pushrods.
What you're after is proper rocker arm geometry with whatever combination of shims and pushrod lenght it takes to acheive that.
Crane has the pedistal shims in a kit of assorted sizes. Comp may have a set also I'm not sure because I just used Cranes kit because it was readily available to me.
Watch the tip of your rocker arm where it contacts the valve tip.
Rotate the engine through 2 revolutions and watch where the rocker tip travels across the valve tip. You want to center that travel area as much in the center of the valve stem tip as possable. You dont want the rocker pushing on one side of the tip only.
Did I confuse you?

You don't need to buy another set of pushrods.

I have the same length in my engine. But with the roller rockers I had to use milled pedestals for around $40 and you can knock $10 off if you send your stock ones back so they can be milled for someone else.

My cam and pushrods were for stock rockers and thats why I had to use the milled pedestals since the RR are .060 taller than the stockers. The max milled pedestals dropped the RR into proper geometry.


I agree with Mike you only need to shim yours.

partnumber for the Crane shims is 99170-1 under $10.


This is extracted from the instructions provided by Doug Macmillin with for installing his roller rocker kits. (Doug sells a Roller Rocker Kit and provides great service) http://v6power.net/rr1.htm

"From Zero Lash: Take your Torque Wrench and tighten to 15 ft-lbs. Notice position of wrench when starting and when finished … it needs to be between 1/3 to 1-1/8 full turns from the original “ZERO LASH” position, and ideally between 1/2 to3/4 of a turn.

if it takes less than 1/3 of a turn with no shims, you need LONGER PUSHRODS. "

Even though I only bought the milled pedestals from Doug he helped me figure out what was wrong and guided me in fixing my preload issue.



My max milled Crane pedestals used with roller rockers are only torqued to 20lbs max.

If you had too little preload ( It looks like you have too much but the thick shim should do the trick) Doug can set you up with a set of Crane milled pedastals for a lot less than new pushrods.

He's not using roller rockers so he cant use those pedistals. Shims and pushrods are his only alternatives.
You had to buy pedistals for your roller rockers? Did they not come with your new rockers?

I know he only needs the shims.

His cam is close to my grind and mine was originally used with the 7.20s and stock rockers. I just put it in for addtional info.

The pedestals that came with my rockers were the stock height. ( I bought them from another SC'r who gave up after his engine blew 100 miles after a lot of work including the new rockers) Since I already had my pushrods it was a lot cheaper to install the milled pedestals.

well here is the problem. I dont have any pushrods yet. I just used a spare 7.200" pushrod that a friend had, to get an ideal of pushrod length. So either way i still need pushrods at least 7.200 long...and if i have to order some anyways...why not get the right length, without using shims? Am i correct?

Yes as long as the geometry is not off when using push rods without shims. This is something noone can give you a definitive answer on ecause each engine is different. You may have had the block decks machined or the heads and that affects pushrod lenght plus you may have had more or less material removed from those surfaces than someone else. The previous owner may have done a headjob where some material was removed from the head surface that you dont know about.
I'm not there to see the rocker geometry myself to tell exactaly what you need to do so will need to describe it best as you can and maye we can figure out the path to take.
The proper pushrod lenght is one that obtains proper lifter preload as well as acheives proper rocker geometry. What I did or anyone else may not work for your engine. How does the geometry look with that pushrod installed?

actually i measured the preload again and i got about .050". I ordered a set of Comp pushrods.....a set of 16 that are 1.195" long. So that should give me the right preload. Also, i colored the top of the valve stem with marker and put the rocker on there, and rotated the engine. Where the ink rubbed off, that is where the rocker is moving. Its almost centered......slightly towards the center of the motor. I think it sould be fine though, as the rocker isn't pushing on only the edge.
Oh one more thing....does anyone know what the formula is for figuring out valve lift? I got a dial on the retainer and it moves .353".....not the .493" valve lift. Don't i have to do something with the rocker ratio to figure it out?

Your geometry sounds fine. You can figure valve lift by multiplying your lobe lift by the rocker ratio(1.73) and that comes out to .59069..........something does'nt sound right here. Recheck that lobe lift because my lobe lift is .284 and we have the same cam.

You guys are making this way too complicated.

You can't check valve lift on a motor with hydraulic lifters. They are going to bleed down a non-pedetermined amount when you try to measure it. Measure the lobe lift and call it a day.

Depends on what you do to the lifters as to how fast or slow if at all they bleed. he is reading lobe lift Dave he just wanted to know how to arrive at valve lift doing the math.

no no..i was measuring valve lift with a dial indicator on the spring retainer. But you are right....i'll never get the right reading with the lifters bleeding down. The lobe lift was .285".... X 1.73= .49305. So i cant measure the actual movement of the valve...and that was what i was doing, and got .353"....so dave was right. Sorry guys.

I'm sorry I misunderstood you. Dave was right you cant measure valve lift at the valve like that with hydro lifters.

ok..yes lobe lift was exactly .285. Thanks guys.

God, I love it when guys talk motors!!!!

Love to see conversations on cams and heads like this on the board. If we all just changed the cams when we did the head gaskets, we would all be happier!!!!!!!!!! Faster too!!!!!!



Don