Originally Posted by oldbogie
It is not necessary to pump up the lifter before installtion and adjustment and not harmful if you do as long as you're aware that each takes a little variation in the initial set up.
For not pumped up:
- Adjust the nut just to the point where any free lash is taken up. You're going to be checking against the spring that want to push the plunger up against the retainer bail or clip so this a bit spongy in feel, it is not necessary to tighten to where the push rod is clamped and cannot be moved at all, this has the plunger bottomed. An advantage to this processs is that the valve will not be opened very far till oil pressure builds in the engine so the lifter to lobe interface will not immediatly be exposed to full spring pressure for a few revolutions.
For pumped up:
- Adjust just till there is just no lash perhaps even a couple thou loose, although for lifters using the wire bale rather than a circlip to retain the plunger running there is a risk of the bail comming out of its groove so this is not something you want to do for long. The plunger is being held against the retainer bail/clip by oil trapped under the plunger, the metering valve to this cavity needs motion to operate properly set the zero lash against spring pressure with the valve closed. If you set the lash a 1 or 2 turns of the retaining nut it will hold the valve open a small amount which will make the engine harder to start as it will bleed compression until the lifters have been cycled enough to bleed off the excess oil trapped in the adjusting chamber alowing the valve to seat. Of course the cam and lifter interface will see full valve spring pressure from the get-go and these days with break-in of the cam being so critical avoiding this situation could be helpful for lobe/lifter life.
The way a hydraulic lifter works is when engine oil pressure exceeds the closed valve spring pressure and a lash exists in the connecting hardware from the lifter to the valve stem tip, the metering valve in the bottom of the plunger is opened by engine oil pressure allowing the cavity between the bottom of the plunger and the lifter's intenral bore to be filled with oil. As the lobe lifts the tappet against the valve spring the metering valve closes trapping the oil in the cavity locking the plunger to the lifter body thus transmitting the motion of the body to the plunger. These opposing forces keep the plunger within the initial adjustment range. The lifter if fully pumped up by the installers action or if in operationthe engine is run at an RPM where the lifters have pumped-up; the only way the lifter can re-establish a proper zero lash position is by cycling off and on and off the lobe. Some lifters have a built in leak like the Rhoads of other anti-pump up lifters and will bleed back down till the valve is closed without cycling, some lifters that shouldn't will still leak enough to do this. All of these leakers that do so by design intent or not are the lifters you hear clatter on a cold start in the morning.
Great post Bogie I type so slow it would take me hrs and soaking my one finger that I type with LOL
I'll add: The lifters that are holding pressure can set for a week or more and still be holding pressure keeping a valve open while the leakers slowly loose pressure letting the valves close! Ive torn down engines after setting for years in the woods that had lifter that still held their pressure!