How to measure lifter preload?

[CARTMAN]

How do you measure for the correct lifter preload and pushrod length? Motor is a stock block, Hyd flat tapped cam, stock heads and rocker shafts. The heads have been milled an undetermined amount block decked, etc. Motor is assembled but has no intake or pushrods

I bought a comp cams pushrod length tool but beyond that I have no idea what to do next to determine correct lifter preload and thus pushrod length.

Please help, thanks

 

[ek02]

I took an old lifter and made a solid lifter out of it with the preload I wanted built into the depth of the solid lifter cup. I marked the tip of the valve stem with a sharpie and adjusted the pushrod length until the rocker arm made a mark in the middle of the valve stem. You want the rocker arm to contact the valve stem in the middle to get the correct geometry. Too long or too short will move the contact pattern either way.

 

[Ttype6]

You want the rocker arm to contact the valve stem in the middle to get the correct geometry. Too long or too short will move the contact pattern either way.

Changing the length of the push rod isn't going to make the roller contact the valve stem in a different location. You have to change the location of the pivot point to do this or shorten or lengthen the valve stem.

 

[ek02]

My engine has GN1 heads with Scorpion stud mounted adjustable roller rockers, and it did change the contact area as the pushrod length was changed. You are correct though with a stock shaft mounted non adjustable rocker. I didn't think about it enough before I posted. The fulcrum does not change with a non adjustable rocker arm. All CARTMAN has to do is put one of the lifters he is going to use on the heel of the cam and adjust the pushrod to the preload specified by the lifter manufacturer. If you know how many thousands a turn is, just zero lash the valve, turn the pushrod adjuster, and then measure the pushrod. You could also put a dial indicator on the pushrod end of the rocker and adjust to the correct preload.

 

[Ttype6]

My engine has GN1 heads with Scorpion stud mounted adjustable roller rockers, and it did change the contact area as the pushrod length was changed. You are correct though with a stock shaft mounted non adjustable rocker. I didn't think about it enough before I posted. The fulcrum does not change with a non adjustable rocker arm. All CARTMAN has to do is put one of the lifters he is going to use on the heel of the cam and adjust the pushrod to the preload specified by the lifter manufacturer. If you know how many thousands a turn is, just zero lash the valve, turn the pushrod adjuster, and then measure the pushrod. You could also put a dial indicator on the pushrod end of the rocker and adjust to the correct preload.

I had hoped they were stud mounted.

 

[Nick Micale]

Unless you had a MASSIVE amount cut from your head and block surfaces, your stock push rods will be fine.

 

[pacecarta]

you should be fine with stock but if you want to measure

http://www.compcams.com/Pages/417/valve-train-geometry.aspx

basically with rockers off drop two lifters in to motor at one cylinder
drop a prod onto the lifters
roll the motor until one rod is up at full lift , youll be measuring the other lobe

remove the prods and install the checker pushrod in the lifter thats down ( on base)

install the rocker shaft (with stock torque down) and adjust the checker until it you have zero lash (lightly rock the rocker up down by hand adjusting prod until rocker just touches the valve stem )

now you can remove the rockers and the checker pushrod ,
the checker is now set at zero lash (no preload)
now you have to add the preload , for stock lifters .030"-.060" is fine
each turn of the tip of the checker is .050" ,
extend the checker rod tip by turning 1/2 to one turn (.025-.050")
without getting into what you need to measure the checker just compare "side by side" the checker to the prods you had , if they match then run the rods you have.
with stock cam and lifters no need to repeat for the other lobe but with custom cams and lifters that run close to zero lash you need to check at more than just one lobe base.

 

[turbofabricator]

I have to respectfully disagree with Nick on this one. I have added .016" shims under a 100% stock engine and gained 2 tenths in the 1/4 mile. The lifter pre-load on the 1987 engines were greater than on the '86 engines. I shoot for .030" pre-load and if you end up with .080" or more it'll kill power. Why?......doesn;t really make sense to me, but it really does. Take your time in setting pre-load and it will reward you with a measurable power gain. ( In my experience anyway). Push rod length can effect where on the avlestem the rocker makes contact, too. (if they are way off anyway) You can just order a setof adjustable pushrods from Smith Brothers and be able to get each valve adjust right on. They usually ship in one day. Lifter pre-load is a pet peeve of mine. I chased a 100 HP loss many years ago and it was due to excessive pre-load. (.150"+) I fixed it with Chevy lifters. Bingo! There was my missing 100 HP. Would have used the correct push rods, but it was a weekend and my wife drove the car to work. Man, those were the days..... of racing it on Saturday and replacing head gaskets on sunday so she could make it to work. That was 23-24 years ago. I got good at head gasket R&R.