Standard hydraulic lifters are designed to automatically compensate for any clearance that is created in the valve train from a cold engine to a hot operating engine. They will also compensate for any clearance that is created from wear or unintentional conditions. The lifter not following the cam profile is the most common unintentional condition. Lifter float or valve float is the more common term. This can be caused from not enough valve spring pressure, over revving the engine, or the wrong cam profile design. When this happens, the hydraulic lifter will “pump-up” to take up the temporary clearance created. Since the initial hydraulic lifter adjustment was set to operate at zero clearance, this extra “pump-up” of the lifter will keep the valve from fully closing until the lifter “bleeds-down” to its original setting. Until the lifter “bleeds-down”, that cylinder will obviously loose compression and power.
Special “anti-pump-up” hydraulic lifters are designed to keep the lifter from “pumping-up” during this condition. There is a strong snap ring retainer in the top of the lifter that stops the lifter plunger travel. The standard hydraulic lifter also has a retainer, but it is usually a weak round wire type. It is not designed to resist the plunger movement. The “anti-pump-up” lifters are adjusted differently than the standard lifters. Standard hydraulic lifters have around a 0.200 total plunger travel. I still do not understand why they are designed with that much travel. Certainly much more then will ever be necessary. Probably to compensate for the “stacking” tolerances (engine, head, pushrod, etc.) in production. The preload adjustment can be set anywhere in this travel range. Normally, the plunger preload adjustment is less than 0.050 when done by hand. All that is needed, is enough preload to compensate for any clearance that is created in the valve train from a cold engine to a hot operating engine and from any wear. In reality, on a cast iron stock engine, this would be less than 0.010. An all aluminum engine may require more. It always amazes me how some mystery is created when adjusting hydraulic lifters. Take a hydraulic lifter apart and analyze it. Look closely at the oil holes, oil channels, check valve, and envision how the oil flows. Make sure you understand how it works. Simple… right? Certainly, no mystery involved. I am referring to a stock OEM lifter here. Special “anti-pump-up” lifters operate the same way as stock ones. The plunger travel is only around 0.050 and they have that strong snap ring retainer. Adjustment is a little different. The idea is to preload the lifter so the plunger will just be touching the retaining ring during hot engine operation. This will prevent the lifter from “pumping-up” any further if valve float was to happen.
The retainer in the standard hydraulic lifter is not designed to resist the plunger travel, so the lifter should be preloaded enough to keep the plunger from touching the retainer during hot engine operation. The preload can be set anywhere within the plunger travel range. I guess this is where the mystery comes in. Usually you hear “quarter turn”, “half a turn” or “one full turn” on the rocker arm nut used to describe the preload adjustment. The plunger can also be adjusted where it is bottomed-out in the lifter. For engines without adjustable rocker arms, the pushrod length should preload the lifter at the midpoint of the plunger travel. All of these will work fine. Take your pick.
Cam profiles are designed a specific way to use a hydraulic lifter. I know all kinds of combinations and lash adjustments are used for camshafts and lifters. I have already stated in previous posts, the disadvantages and dangers of mismatching cam profiles and lifters. I will just continue to shake my head and be amazed at why this is done.