How to measure Lifter Preload

[T-top87GN]

Hey guys! A friend of mine has been having some trouble with his motor. He got a Jaspers rebuild and asked them to put a bigger cam in it. Well, it's wiped 2 cams now. Talking with another buddy he suggest I check the lifter preload when we get the new cam back in and get eveyrhting bolted down.

Basically we are thinking a couple things here: 1) Jaspers obviously doesn't know about turbo buick motor and prolly threw too radical a cam in there for the stock valve assembly. 2) The heads or deck have been shaved. So with this in mind I plan on checking the lifter preload before we put it back together.

My questions is, where do I measure the preload at? do I use a wire feeler gauge? what are the acceptable ranges for lifter preload? where should the lifter be at on the cam when I check for the preload?

Thanks guys!

 

[U1ARUNIT]

In General, the proper lifter preload for a LC2 motor is .030 - .035
inches. More preload will give you a stronger top end and less preload,
a stronger lower-mid range. One easy way to measure this is to A)
remove intake manifold, B) rotate engine to TDC on any one cylinder, and
C) using a wire-type spark plug gapper, measure how far the plunger of
the lifter has been pushed down from its seat (thanks to John Pearcy for
this one.)

On a motor where you have changed something in the valvetrain
(camshaft/lifters, head thickness, new/different head gaskets, new
rockers or roller rockers), you need to determine the proper length of
pushrod to attain the amount of lifter preload you want. To do so
requires that you buy some .010" shim stock (available at machine shops,
larger NAPA's, etc.) to make some shims (cut out a rectangle and drill
hole in middle.) Using the pushrods you have now, install the
rockershafts with X number shims between the rockershafts and the
mounting bosses on the heads. Torque the shaft bolts to 25 ft/lbs. X
will be the number of shims required to attain zero lash. This is
attained when the rocker does not move around on its own and there is
zero preload on the lifter. If, for example, this occurs with 5 shims
(.050") installed and you want lifter preload to be .030", then the
proper pushrod length will be .020" shorter than the pushrods you are
using presently.

 

[T-top87GN]

Ok so I want to check with everything tigthened down and the lifter NOT sitting on the bump in the cam (ie TDC).

I measure from the little piece of wire that holds lifter plunger in the lifter, to the top most point of the plunger.

Is that correct?

 

[U1ARUNIT]

Yep, tightened down and on the heel(opposite of the ramp/lobe) of the cam.

Let us know what you find out.

 

[T-top87GN]

Alrighty! I'll let you know as soon as we get it back together!