I tried asking this question on the C1/C2 forum when somebody posted a question on hydraulic lifters. Nobody had an answer. Thought I’d ask over here. I’m putting the upper end of my motor back together and was setting the preload on the hydraulic lifters. I was following an article by Lars from the forum that follows the method of tightening the rocker arm until the pushrod just stops rotating with finger pressure, then adding ½ turn more. (With the cam on the base circle for the lifter being adjusted.)

The strange thing was if I came back to the lifter a couple of minutes after setting the preload, I could rotate the push rod again. It wasn't loose; it just felt like the pressure applied from that extra 1/2 turn rotation was released. I'm assuming I had pushed the oil out of the lifter, but I really don't know and I have looked everywhere to see if someone addresses this phenomenon.

Anyone have some words of wisdom?

 

yes...when you first set the preload its feels tight. the as it rersts for a while the oil gets pushed out of the lifter. when you start the engine the oil pressure comes in and takes up the slack. the preload is the amount of distance the lifter plunger is pushed down in the bore. As the valve train components wear over time, the plunger moves up and takes up the slack.

 

John:

Thanks for the reply, nice to have a sanity check. This was something nobody ever mentions.

I'm also curous if you set preload on a lifter and let it set for the oil to get pushed out. Then backed the preload off, will the lifter refill with oil? Or will it fill with air? I'm guess I'm asking this because if you set preload and then had to back everything off because you forgot something (a trademark move of mine), can you still use the 'tighten then add 1/2 turn' technique?

 

I would think that for proper load reseting you need to make sure there is fresh oil on the lifter. The will not be a big deal if you have been running the engine though. But can someone explain the negative effects of overloading the lifter? or just the effects of it for that matter? why can they not perform as well as solid lifters at high rpm?

 

Its no problem if you have to back it off and do it again. There is a spring in the lifter body that pushes up on the plunger. So even if the lifters were dry you should still be able to feel the point at which 0 lash is reached. when I adjust lifters with the intake off, I also watch the plunger in the lifter. As soon as you pass 0 lash the plunger will begin to move down in the lifter. It takes good lighting and a sharp eye, but you can see it. What happens when you adjust valves in an engine that has already been run is, when you take it down past 0 lash the valve is actually pushed open a bit. But as it sits, the pressure of the valve spring overcomes the pressure in the lifter plunger spring, and the valve closes back to seat as the plunger in the lifter goes down. Its also why, if youve ever adjusted lifters when the engine is running, once you take it down past 0 lash the engine stumbles for a momment or two as the valve is not seating all the way. But the valve spring pressure quickly overcomes the lifters load and the valve begins to fall back to seat fully. so hydraulic lifters are always at 0 lash if adjusted correctly. The preload is added to take up slack for wear of parts as time goes on. If the lifter preload is to much, the valve spring may not alweays be able to overcome, especially at higher rpms when the oil pressure is higher. When this happens there is loss of compression since the valves arent closing all the way. Whether you adjust 1/4 or 1/2 past 0 doesnt really matter a whole bunch. one setting will last longer before needing to be re- adjusted. I usually go 1/2 turn on a brand new cam and lifters and 1/4 on ones that have already been run for some time.

 

Hey, we answered ya!! :) Don't think you asked this PARTICULAR question though. Nice to see you got what you were looking for. :cheers:

 

John:

Thanks again. You're advice sounds right on. I did have the manifold off when I set the lifter preload but didn't think to watch the lifter plunger depress.

Hope to start the Vette up on the fourth - without any fireworks.


Dave:

No offense meant to the C1/C2 forum as I piggy-backed my question onto someone who had posted a lifter problem (see bondo478's post). My question probably got lost in the noise. I am continually amazed at the information available through Corvette Forum.