Whats the difference in more or less lifter preload on hydraulic lifters. Right now if preload 1/2 turn. Ive read that some preload 1/4 turn. Any difference?
Whats the difference in more or less lifter preload on hydraulic lifters. Right now if preload 1/2 turn. Ive read that some preload 1/4 turn. Any difference?
the more preload you do, the more it'll pump up at higher rpms due to excess oil pressure. you can run em at zero + 1/8 a turn preload and get alittle more outta a cam. some peeps will run zero lash and that's it, but i'd worry about em comin apart without good retainers in the lifter.
So how does less preload give you more out of the cam? I don't get it. Wouldn't more preload give you more valve lift?
So how does less preload give you more out of the cam? I don't get it. Wouldn't more preload give you more valve lift?
less preload makes the lifter "pump up" less at high rpms and float the valves.that's what prob i was havin when i switched to the high rev lifters. when i'd let outta the throttle with the old lifters, it'd run rough till the lifters bled off alittle from pumping up bad, doesn't do it anymore after the lifter swap.
Pump UP? So with to much pre load which depresses the plunger in the lifter, when the oil pressure pushes the plunger back up it causes valve float? Is this an accurate explanation?
Pump UP? So with to much pre load which depresses the plunger in the lifter, when the oil pressure pushes the plunger back up it causes valve float? Is this an accurate explanation?
close enough, yep
Yea Taylorman, that's a pretty close explanation. Fortunately, the performance lifters these days (especially the ones designed to "bled down" at idlelike a Rhodes, bleed oil through them at a faster rate which effectively holds off lifter "pump-up" untill higher RPM than "stock" lifters.
My Isky's are supposed to not pump-up untill 7,000 RPM. I can tell ya thay won't pump up at 5,000.
Taylorman, dump some PMs, you're full up............MP
Okay, here's a question. I've been working on a friends 496HO(he broke a rocker arm where the pushrod contacts it, it pushed through the arm)...anyway we upgraded a bit and got some Comp Magnum ones with roller tips, but still the non-adjustable type. So, I'm installing the new rocker arms and I set it to zero-lash and from there it takes another 2 1/4 turns to bottom out the nut...which I know is way too much preload, so I thought the rocker arms were the wrong ones for the engine...but just to check, I installed one of the old ones on that same stud and it took 2 turns for the nut to reach the bottom.. Is that right, or not? The motor has never been apart before, so I figured it had to be right. I did the same thing on a few others and the same thing...and yes the lifter was on the base of the camshaft. I'm not sure what to do? Do I tare it apart again and get some shorter pushrods for it? Or is it fine as is? This is my first experience with a 496 and a non-adjustable rocker arm set up...
Thanks
Troublemaker:
I believe we spoke on the phone the other day? On hydraulic lifters in most BBC blocks, the fine threads on the rocker studs will depress the plunger in the lifter about .035" per turn. Most stock and aftermarket hydraulic lifters have about .90-.120" total travel in the plunger in the lifter and generally we don't like to see more than about .040" of that used for preload. This leaves about .060" to .080" of lifter hydraulic action to the valve train. This usually means that 3/4 to 1 turn is more than sufficient. If your buddy's motor is taking two turns even in stock form, I would think something here is just not quite right. You can remove the studs and put a .060" hardened washer under each one and get to a 3/4 to 1 turn adjustment. Stock 496's have some pretty weak pressures on the valve springs and if this motor has a weaker than normal set because of heat or wear you might be getting an unstable valve train scenario which can destabalize the valve train so much that wierd things start happening and breaking. Check the valve springs and make sure they are within spec on poundage on the seat (should be about 90lbs) and poundage open(should be about 280lbs.) Just some more info, be careful though, wandering valves can really destroy a motor quickly as you know.
Ray @ Raylar
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