I was attempting to adjust the hydraulic lifters/valves on my '74 smallblock when I ran across something that I think is probably much more than a $%&* nuisance.
One of the lifters feels "spongy". I can shove the pushrod down with my fingers, and it rebounds right away. It is difficult to feel the "zero lash" position, and easy to blow right past it.
What's up with that?

 

Had the exact same thing happen before. The check ball in the lifter is stuck open and isn't holding the pressure under the piston. When running (normal conditions) you'll probably never notice (if you can get it set) since it'll be constantly "re-filled" and as it moves up in the hole. yes not as solid as if it is working right but not asd spongy like you feel now) Right now it'll be empty and all your feeling is the spring inside.

Fixing it is a different story, sure-fire method means pulling the lifter apart.
Search it through and you'll find many many sites with suggestions on all kinds of possible solutions (marvel mystery oil, etc) your mileage may vary
M

here's a pic


With that little check ball stuck open, the oil leaks back into the body of the lifter so what your feeling is just the little spring underneath. With teh checkvalve working, (and no pressure) it traps the oil under there and acts like a (sort of) solid block and resists you pushing down on the rod.

 

It is VERY easy to blow past the 'zero lash' point if the lifters are not pumped up with oil. That's why I use the "jiggle" or "shake" method of finding that lash point, rather than the "spin" method.

If you shake the pushrod up and down as you are tightening the adjustment screw, you can easily find the place where there is NO SLACK left. That is the Zero Lash point. The pushrod rattles as you are shaking it; when the rattle disappears, you're there.

 

Well, I was worried that the circlip on the top had fallen out, and the only thing holding the lifter together was the load from the pushrod.
Does that sound likely?

 

Not really. If the retaining clip had come out, the plunger seat would have been ejected by the spring. Most likely, the lifter just didn't have any oil inside of it.

 

Unless it came way out (you unlashed the thing to where it basically came apart) it would still hold pressure under the piston and not feel spongy.

I can't see how anything other than managing to get air in there somehow or a stuck check ball can result in the spongy feel as you described. I've had it before and took the lifters apart and checked them, stupid little ball stuck open in the cage.
Even went back and forth with Lars trying to see if there was anyway to bench test them, doesn't actually seem practical.
Do the very best to set the lash as you are and live with it. There is a chance it'll free itself after awhile.
Otherwise, blow it all apart and clean it and put the same lifter back in the same hole.
M

 

Before I install hydraulic lifters, I stick them in a can of motor oil and use a pushrod to pump each one a few times to fill them with oil.

Some folks say it's not necessary; but it's not much trouble for a little extra 'insurance'.

 

Not to beat the subject to death, but....
It seems that I feel two different spring rates. At first, the resistance is very light, and then at some point as I turn the adjusting nut down, the resistance increases dramatically, and the valve begins to open. If I stop there and wait for a minute, the valve will close again as the lifter slowly adjusts itself to the preload. (I am filling the cylinder with compressed air with a leakdown tester at the same time, so I can tell).
That can't be right, can it?

 

That's perfectly normal.
The lifter is in the "down" position and the oil can be forced out of the oil passage that the oil normally enters when the engine is running and the oiling system is pressurized. That's how the hydraulic lifter takes the slack out of the system. The check valve does close but it isn't, and shouldn't be, perfectly tight so without oil pressure from the pump some oil will get past the valve.

The answers given to you by Mooser are basically correct, but only under the right circumstances!
Normally the lifter should be filled with oil when you stop the engine and should not feel "spongy"; however once you tighten the adjusting nut past the point of just taking the slack out of the pushrod then you will force the oil out of the lifter and only the spring will be left to hold the pushrod up. Hence the "spongy feel", or perhaps we should call it the "springy feel"

Lots of folks will tell you how easy it is to adjust hydraulic lifters. That's true if you are used to doing it (like with everything else) but for first timers it really is quite difficult. The "shake up/down" method described by 7t1Vette is safer to use for amateurs like us. Tighten the nut bit by bit while moving the pushrod up/down.

Regards
Karsten

 

So what you are saying is just that particular lifter is behaving that way because it is only partially filled with oil? And that's why I can shove the pushrod down partway with my fingers?
So once the engine is started, the lifter will fill with oil and run fine? What has me concerned is that it is only the one lifter that feels that way. All the others have a very definite stiff/loose point.

 

What's the preload that you set the lifters at?
Bob

 

Yes, but only if you had it tightened past the point of just taking the slack out of it. It was my impression that you did that? If it was already loose before you started adjusting, and the rest of them weren't, then something is wrong.

 

Instructions for the Edelbrock 2102 say zero lash plus one half turn.

 

I was thinking of getting an oil pump priming tool, spinning up some oil pressure, and seeing if that changes/improves things. Because I'd hate to tear the top off the engine for no good reason.
Whaddya guys think about that?