David Vizard's Idea of Almost Bottoming Hyd. ? - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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  #16 (permalink)  
Old 06-22-2010, 02:00 PM
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Quote:
Originally Posted by cobalt327
OP- can you please provide a link to the Vizard instructions you cite?
They are in Vizard's book/tech manual "How to Build Max-Performance SmallBlock Chevy's on a Budget".

He is working off the idea that at high rpm the lifter collapses due to aerated oil and allows the valves to return to the seat too hard, not following the closing profile of the cam lobe, resulting in seat bounce which kills power. The only way the lifter will pump up is if the valvespring looses control of the rest of the valvetrain, he does say that you have to know that you have good valvetrain control to do this mod.

I've never messed with this, just read the info in the book(which actually has loads of good info), in my mind anything performance should have solid lifters anyway.

To quote Joe Sherman... "Hydraulic lifters are for girls!"

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  #17 (permalink)  
Old 06-22-2010, 02:38 PM
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Where the OP threw me a curve was by saying that the lifter was 0.010" or whatever from BOTTOMING.
Quote:
Any comments on David Vizard's idea of almost bottoming hydraulic lifters?
To me, that means the plunger was compressed into its bore almost all the way, not at the TOP of the plunger's travel.

All that is being said by Vizard is just another way of the old "1/8 turn" deal, aka zero lash-almost.
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Old 06-22-2010, 02:42 PM
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Last edited by cobalt327; 06-22-2010 at 02:44 PM. Reason: Totally OT.
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  #19 (permalink)  
Old 06-22-2010, 02:47 PM
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Quote:
Originally Posted by cobalt327
Where the OP threw me a curve was by saying that the lifter was 0.010" or whatever from BOTTOMING.
To me, that means the plunger was compressed into its bore almost all the way, not at the TOP of the plunger's travel.

All that is being said by Vizard is just another way of the old "1/8 turn" deal, aka zero lash-almost.
NO! Vizard is saying to run the lifter plunger within .010"-.015" of fully bottomed out, so there will be no aerated oil in the lifter to allow the lifter collapse which could happen with a zero lashed or factory spec lashed lifter.

He advises setting them with a leakdown tester plumbed to the cylinder so you can tell when you are holding a valve off the seat and back off just enough to close the valve, then remove the feeler guage.

He says that doing it on a running engine takes a good ear for when you have reached bottomed out and are holding the valve slightly off its seat as it will create a miss in the running engine that is tougher to get a read on.

I understand the theory, and how it is done but have never messed with it.
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Old 06-22-2010, 03:05 PM
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Sounds like nonsense to me, if you have aerated oil in the lifter gallery your going to have worse problems other than running out of rpm...like spun mains or rod bearings. Seriously when is aerated oil ever a problem these days? Your oil level would have to be too high or using some kind of non-detergent oil to have this issue?

I understand the concept but have no idea where this would have any application in the real world except to limp home with a collapsed lifter. My question is, if the lifter is collapsed and you have next to zero clearance whats preventing the lifter from pumping up again and holding the valve open? I am willing to bet as soon as you run into valve float that lifter gets enough free clearance to fill with oil again and hold the valve wide open, sounds like a perfect opportunity to blow the carb off at 6500 rpm with a huge backfire.

I wonder if this conversation is going to turn to filling lifters with epoxy to make them solid (yea its been done).
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  #21 (permalink)  
Old 06-22-2010, 03:13 PM
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Quote:
Originally Posted by BUFFALOBILLPATRICK
He uses a .006-.010" feeler gauge between the valve stem & the rocker tip, while running motor at 1,000 RPM

He tightens the rocker stud nut until there is a slight miss from the valve not closing all the way, backs up until miss goes away.

This makes the hydro lifter plunger .010-.020" from bottoming out inside the lifter, depending on rocker ratio.

It's in his book: How to Build Max Performance Chevy Small Blocks On a Budget.
Pg 105-106

BBP
Something's wrong with this statement, if you bottomed the plunger the push rod would be too short and would need a longer push rod to adjust the rocker so it engaged the valve stem correctly.

Bottoming the plunger also provides all that travel distance from where it is to the top of its travel in the lifter body as space in which the plunger can take up any lash that forms. This sounds like an edit error or a way for Vizard to win more races.

Bogie
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Old 06-22-2010, 03:16 PM
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Quote:
Originally Posted by 4 Jaw Chuck
Sounds like nonsense to me, if you have aerated oil in the lifter gallery your going to have worse problems other than running out of rpm...like spun mains or rod bearings. Seriously when is aerated oil ever a problem these days? Your oil level would have to be too high or using some kind of non-detergent oil to have this issue?

I understand the concept but have no idea where this would have any application in the real world except to limp home with a collapsed lifter. My question is, if the lifter is collapsed and you have next to zero clearance whats preventing the lifter from pumping up again and holding the valve open? I am willing to bet as soon as you run into valve float that lifter gets enough free clearance to fill with oil again and hold the valve wide open, sounds like a perfect opportunity to blow the carb off at 6500 rpm with a huge backfire.

I wonder if this conversation is going to turn to filling lifters with epoxy to make them solid (yea its been done).
I would never stoop to filling a perfectly good lifter with epoxy, that's like parachuting out of a perfectly good airplane,,, dumb idea.

But now filling one up with washers holds some merit.

Bogie
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  #23 (permalink)  
Old 06-22-2010, 03:17 PM
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I don't think this is intended as a street or drag application, I think it is intended by the way it is worded in the text just for circle track engines where rpm is always high and oil is going to get aerated no matter what you try to do to prevent it.

He does say you HAVE to have good valvetrain control and "foot sense" enough to stay out of valve float when set like this.

The man is no dummy, and has done a lot of testing and racing, and is highly respected in his field. Can't just dismiss it as baloney.
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Old 06-22-2010, 03:24 PM
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Might work, if the pushrods are measured for correct geometry w/the lifters collapsed (less 0.010").

And you were sure the oil was aerated and that this air was in fact lodging inside your lifters.
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Old 06-22-2010, 03:32 PM
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I copied this from another board.

"We did a lot of testing on this back in the 80's.
The problem isn't with the lifter pumping up, it's with the lifter bleeding down at higher RPM's.
It's like the lash opening up on a solid lifter cam. Not only does it shrink up the effective duration(hurting the top-end HP), it makes the effective valve seating velocity extremely high(causing seat bounce)."
Mike Jones
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  #26 (permalink)  
Old 06-22-2010, 07:38 PM
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Hmmm

Not sure if I'm following this correctly, I don't know if we are bottoming the lifter or running close to zero lash. I recently said that in my experience,stock cams in small blocks run a hell of alot better with a full turn or a turn and a half of preload. On the other hand, high performance cam and LIFTER packages run better with a quarter to a half a turn of preload. I don't know how far you can crank down on a stock or HP lifter without holding the valve open, but it seems, it runs out around two full turns. So for this Vizard trick, it may depend on the lifters used? Comments? olnolan
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  #27 (permalink)  
Old 06-22-2010, 11:32 PM
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I think that the problem here is that people are just not entirely getting what the lifters are doing, and honestly, I'm not sure that I get it 100% either.

This is the part that I'm following:
The hydraulic lifters are used to take up the slop in the valvetrain. To that effect, when they are on the base of the cam lobe there is extra room for them, so the oil pressure can fill the lifter lifting the plunger till it takes up the slack. As the lifter rides up the ramp the spring pressure of the valve train puts pressure on the plunger and the oil leaks out of the lifter, effectively decreasing it's size.

At higher rpms oil pressure increases (probably actually has very little effect besides more effectively/faster refilling the lifter), and there is less time for the lifter to bleed down so hopefully the resultant loss of lift is less when the engine really needs more lift/duration (Rhodes and similar lifters take this further by leaking down faster more significantly decreasing lift and duration at lower rpms resulting in the cam acting "smaller").

This seems to make sense WRT this discussion... if you tighten down the adjusting nut to the point where it compresses the plunger all the way then there is no place for it to go so there is no way for it to loose lift, so the engine makes a little more power. The only time that this should be a problem is if you float a valve, resulting in some extra room in the valve train, making room for oil to pump up the plunger, and when the valve catches up again the pumped up lifter will take some time to bleed down and can prevent the valve from closing.

The part that I can't explain is why would setting them as close to 0 preload as possible (typically the 0+1/4 or 1/8 turn thing that most people talk about) would help any at all... as far as I can tell all that does is gives them more room to bleed down, so I can't seem to explain why this would make more power (as a matter of fact, again, the further they're tightned down and the less room they have to bleed down the more power i would expect it to make, so the stock 1-1.5 turns past 0 should make more power, but I'm pretty sure that I've seen going as close to 0 lash as possible helping extend the top of the power band some, which again, I can't explain).

Can anyone out there fill in what I don't seem to know?
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  #28 (permalink)  
Old 06-22-2010, 11:42 PM
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While I'm at it... really rather than adjusting things till the plunger is all the way tight it would seem to me that making a spacer that is slightly smaller than the space that the plunger has to move limiting the total amount that it can move would have the same result WRT to lift/powerband without the potential problems when you float a valve.
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Old 06-23-2010, 09:29 AM
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I copied this from another thread.

"The only reason you can't run a hydraulic lifter on a solid cam, is the added spring pressure the high lift solid cam would require.

The guys that will be making the most power at the EMC will be using solid roller cams, and the limited travel hyd roller lifters. They will set them .010-.020" from bottoming out, and up the spring pressure to the point that the hydraulic system on the lifter no longer works.

In short, they will be running them as solids."

Mike Jones
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Old 06-23-2010, 11:05 AM
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I may need a longer pushrod, I will check "witness marks" on top of valve stem.

Method: apply black marker to top of 1 cylinders Ex. & In valve stems, install & adjust rockers, & turn engine over by hand. Remove rockers.

Observe: Rocker pressure will wipe black marker at contact area. This should be centered & toward the intake side, NOT TOWARD THE EXHAUST SIDE. Contact area should be as short as possible.

BBP
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