I need some help figuring out exactly how hydraulic lifters work. I know that there is a plunger that the pushrod sets in and that it slides into the lifter when we preload it. But why can we use different amounts of preload? 1/4 to one full turn after zero lash. Does that not affect the overall lift we are getting out of the cam? Or does it just set the depth of the piston into the lifter and that stays constant. In my head, I guess I thought that the lifter pumped up and pushed the cup up in the lifter, but I'm not so sure now.
Yesterday, I readjusted my lifters. Initially, I had adjusted the lifters while the engine was running to 1/2 turn in after they quit making noise. Then I read on the Comp and Crane cams websites how to do a static preload on the lifters while the engine is off. That is what prompted me to redo mine. I found out that even though I had adjusted the lifters 1/2 turn after quiet, that actually in a static situation, they were all adjusted to zero preload. Which means that I had to tighten down the lifters an additional 3/4 to 1 full turn, approximately 7/8 to be on the safe side, to get the required preload. Did I increase the lift I am experiencing or is my pushrod just further down into my lifter?
My car sound different to me at idle and it seems to run better than ever. What do you guys think about this?
When doing the static type of adjustment, Its best to back the nut off some to make sure the pushrod and lifter plunger is totally unloaded.
Hydralic lifters have a spring under the plunger to keep it pushed up against the snap ring when not under any load. What Crane and Comp want you to do is to make sure the lifter is on the lowest part of the cam lobe, then slowly rotate the pushrod with your fingers while tightening down the rocker nut. Once you feel the pushrod start to drag, turn the rocker nut to their specs, usually 1/8 to 1/2 turn.
The 7/8 turn you mention sounds pretty scary if it is indeed that far down. The 1/2 turn is to give the lifter some margin of automatic adjustment as things wear. If you tighten them too far, its possible that you will compress the plunger inside the lifter all the way down and the valve will not close completely, resulting in really bad performance and low/no idle vacuum.
The preload, for the most part, does not affect the overall lift of the cam. It just gives the lifter some working room. If you do happen to over rev the engine, the lifters will usually "pump up" ( the oil fills the lifter all the way up including the preload distance) and the valves will float, as in not completely close. This can be a good thing as it will keep the engine from going balistic and making a mess in the street. Also, if you over rev the engine, the springs will probably not be able to keep up and that will limit the rpms too. Most stock lifters and valve springs will "float" around 5 grand, which is pretty high for most stock engines.
If you are building a performance engine and are expecting to rev higher than stock, then you will want to use "anti-pump up" lifters and valve springs that are rated for higher rpm use.
Well a standard hyd. lifter has a spring in it to keep the plunger up and a oil galley in the side. The lifter guide has a oil galley in the side as well and when the engine is running oil pressure keeps the plunger up and also lubricates the lifter.
As for chebby lifters and pushrods.... just buy olds.. :thumbup:
Thanks for the reply, I was kinda worried about over tightening the valves when I did this. But after the adjustment the car started and idled fine with throttle. Plus, the car seems to run better than ever.
Comp cams recommends 1/2 to 3/4 turns static, Crane recommends 1/2 to one full turn. It obviously is not holding the valves open, but to my orignal question, do I get more lift?
So I am just pushing my pushrod down further into my lifter, and the running better is all in my head. Wouldn't be the first time.
I can't explain it, but I've experienced the same thing. My '72 Nova with 350 & L82 cam idles smoother & takes off easier from a dead stop with the lifters one full turn down from zero lash, as opposed to 1/4 turn down.
87442lover got most of the info about the lifter but there is a tad bit more. As the lifter gets raised by the cam lobe the piston in the lifter gets pushed down and will cover the oil hole in the side of the lifter and not allow any more oil to get back out. In essence you now have a solid lifter because the oil will not compress so the push rod then pushes the rocker which opens the valve. By tightening the adjustment up that extra 1/2 turn you will cause the valve to open just a fraction sooner, hence you get that seat of the pants good feeling because the throttle response is RIGHT there RIGHT NOW. The down side is if you over rev the engine like miss a gear then you could "float" the valves which then might give the top of the piston a little kiss. Because the valve stays open when it should be closed.
But to answer your question, no you do not get more lift from the cam grind you just get it's lift working a little sooner.
Chevy engines you can adjust but Cadillac engines are non-adjustable so if they are too tight or too loose then you have to buy different length push rods to get the lifters in the middle of that lifter piston travel. A lot of Fords are like this too. You just torque the rocker and the lifter takes care of itself.
That makes sense to me. The engine is a 400 sbc with a mild comp cam, 256H, good heads and intake - Trick Flow 23 degree with an RPM Performer and 700 Edlebrock Carb and 1.6:1 aluminum roller rockers.
With the lifters set the way they were, at zero lash, the car ran fine but the valve train always seemed a little noisy. Now that they are adjusted down 7/8 of a turn the valve train is quiet and the car feels more responsive at all RPM ranges.
It is hooked to a 700R4 converted to nonelectric and I don't normally shift it manually so the engine does not get over-revved, it is more of a torque monster.
Thanks for your explanation.
As for chebby lifters and pushrods.... just buy olds.. :thumbup: [/B][/QUOTE]
Not good advice! Just because something fits doesn't mean it's right.
Chevy's are all .842". Fords are .875" Olds/Pontiac are .842" also but the oil band is in a different location compared to a Chevy. Now you could use
a Chevy lifter in a Pontiac/Olds as long as the cam was not over .475" lift. Anymore and it will starve the engine for oil. Your safest bet is to buy the retro hydraulic rollers. $600 is not bad, I know first hand how much money it cost to do a short run of these.
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