Itinerant Air-Cooled

Amskeptic wrote:The lifters only release oil during the valve-closed period

There seems to be some muddle in the picture of where the lifters bleed down going on in the swirl of my brain,

• According to Engine Builder Magazine the bleed down comes from between the plunger and the lifter body, a clearance we commonly know as the tightest in the entire engine. They go on to say that by changing the clearance you can change the bleed down rate.
  
  Richard Atwell talks about how when the lifter is finished with a rotation cycle the valve spring seats the lifter body at the base circle of the cam where it can, due to no longer being under as much pressure, have the check ball released by the gallery oil pressure at which time the plungers pressure equalizes and the lifter self adjusts.

So, I wonder if I have a clearance problem, a gallery oil pressure problem, both, or a problem with the Gods. Perhaps it doesn't fall into any of these categories at all.

Tim still having fun with this hopefully

hydraulic lifters leak at a set rate. It is in their design. They take in oil thru the check valve any time there is clearance and the oil gallery is in alignment. There is X amount of oil pressure. At higher RPM's that pressure trying to fill the lifter is offset by weakening valve springs which in turn are pushing on the rockers and pushrods. The weakening comes from oscillations of the valve springs and the fact that they have a set recovery rate each time they are compressed. To compensate, stronger valve springs than those for solid lifters are used to keep the hydraulic lifters from pumping up at the higher RPMs. Because a fluid cannot be compressed, there is no internal pressure in the lifter trying to push oil out - instead it is the pressure of the pushrod on it that is the acting force. VW engines with hydraulic lifters are of a poor design because they are almost laying on their side, and that allows entrapment of air. That air compresses and allows the lifter to knock until the air is purged. But hydraulic lifters required less maintenance and that is what the public and government wanted.

Funny, according to Wikipedia's hydraulic lifter article: "It is a myth that in certain circumstances, a lifter can "pump up" and create negative valve clearance."

Guess the Wikipedia contributor doesn't drive a VW bus.

Okay, so Wikipedia is hardly an authoritative source, but the article does make this additional interesting point: "The problem is due to weak valve springs which permit float at high engine speeds. The followers attempt to take up what they see as extra clearance."

It's pretty clear that the lifters and springs have to be a close match to one another for the lifters to work as intended. Have all of the problems that recently reported been on newly-rebuilt engines? Are we just seeing a rash of lifters which were built just enough out of spec that they don't play nicely with the installed valve springs? Or perhaps we're seeing a rash of weak valve springs?

SlowLane wrote:Funny, according to Wikipedia's hydraulic lifter article: "It is a myth that in certain circumstances, a lifter can "pump up" and create negative valve clearance."

Guess the Wikipedia contributor doesn't drive a VW bus.

Okay, so Wikipedia is hardly an authoritative source, but the article does make this additional interesting point: "The problem is due to weak valve springs which permit float at high engine speeds. The followers attempt to take up what they see as extra clearance."

It's pretty clear that the lifters and springs have to be a close match to one another for the lifters to work as intended. Have all of the problems that recently reported been on newly-rebuilt engines? Are we just seeing a rash of lifters which were built just enough out of spec that they don't play nicely with the installed valve springs? Or perhaps we're seeing a rash of weak valve springs?

The pumped-up lifter issue with valve float has serious consequences that we are not dealing with here. In that high-rpm scenario, you can get valve/piston contact and bent pushrods, etc.

Our issue is that the lifters refuse to open the check valves at rest, with the screws backed out, no operating pressure . . .
Colin

Hi. Thank you for the invaluable response I got. My issue was with valve sits damaged