Correctly setting valve lash.

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DeCaff2007

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I'm trying to set the valves on my mostly stock build. The service manual is too vague. "Tighten the rockers arms while spinning the push rods until they don't, then tighten the rocker arm nut another 3/4 turn." Well, every push rod seems to spin at a different, um, tightness. Does that make sense? Then sometimes that extra 3/4 turn seems TIGHT, then other times it's normal.

Before anyone asks: YES, I soaked the lifters in oil.

Is there a more definitive way to do this?

In case everyone doesn't know by now: 88 RCSB with a 94 5.7L, stock flat tappet cam, and hydraulic flat tappet lifters.
 

DeCaff2007

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Ok thanks. That actually made sense. I don't have a harmonic balancer that's marked every 90°, though.

I guess that means go through every other cylinder in the firing order, rotate the balancer 180°, then do the other cylinders.
 

tpass

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You can just mark it with a yellow crayon or something, it doesn't have to be exactly on the mark to adjust the valves.
 

Schurkey

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There's two dozen ways to adjust lifter preload, and they ALL work if the guy doing it knows what he's doing. Some ways are more-complex than others. The more complex the method, the more it's intended for solid lifters that need lash rather than hydraulic lifters that need preload.

The BIGGEST PROBLEM folks run into is when they "spin" the pushrods looking for "zero lash". THIS IS A REAL TROUBLEMAKER. Your ability to "spin" the pushrods varies depending on how strong your hands are, whether your fingers are oily, and how stiff the springs inside the lifters are. I've seen guys "spin" the pushrod while tightening the rocker adjuster nut, to the point that the lifter plunger is TOTALLY collapsed, then they add preload which means the valve CANNOT close. Engine runs rough, or doesn't run at all.

DO NOT "spin" the pushrods.
Pull up on the pushrod end of the rocker arm, and let the rocker arm drop down onto the pushrod. You'll go from having actual clearance (rocker arm flops up and down) to tightening the rocker adjuster nut gradually removing that clearance (rocker flops progressively less up and down) to achieving "zero lash" (rocker is just at the point of having no free-play "up", but may be FORCED down against the spring in the lifter)

"Zero lash" is the prime target, it's what you MUST achieve in order to get consistent preload.

Once you have "zero lash", you merely add "your choice" of preload. Some guys like 1/4 turn of the adjuster nut, some guys want 1/2 turn of the adjuster nut. For decades, Chevy said to add 1 full turn of the adjuster nut. I've seen OEM hydraulic lifters with more than 1/4 inch (250 thousandths) of plunger travel. I've been sold hydraulic lifters that had about ten-thousandths of plunger travel, and no warning on the box that they're reduced-travel lifters.






The absolute fastest, simplest, easiest way to set lifter preload: Crankshaft can be in ANY position, does not have to be at "0 degrees" as shown on the damper/timing pointer--but that's recommended. Otherwise you have to mark the damper manually with a paint stripe or yellow crayon, or something.

Loosen all rocker arms so they have free-play.

Tighten all rocker arms so the free-play is gone
, but don't go beyond the point of eliminating free-play.

Rotate crankshaft exactly one full turn. Either go from "0 degrees" back to "0 degrees" as shown on the damper, or mark the damper with a paint stripe, and turn one turn so the paint stripe is back where it was.

SOME of the rocker arms (fewer than half) will be loose again--having free-play. Tighten ONLY the loose ones so the free-play is gone, but not beyond. Leave the "tight" ones alone. All rockers are now at zero lash.

Tighten ALL rocker arms "your choice" of preload. "Your choice" varies depending on the available plunger travel of the lifters--know what you bought!

Put the valve covers on, and have an adult beverage. You're done.

For the record, "soaking" lifters in oil is a TOTAL waste of time. It does NOTHING useful. If you submerge the lifters, and then pump the plunger, you might get the oil inside the lifter. When it's me, I use a pump-style squirt can, and fill the lifter with oil (ATF, it's thinner) under pressure. This means I can verify the leakdown rate of the lifter, and it proves that the lifter will pass oil to the pushrod seat. It also means that when I add preload, I'd better do it slowly so the lifter plunger has time to bleed-down.
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1990Z71Swede

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Is there a more definitive way to do this?
Incidently just stumpled upon this yesterday.
Looks cool, but obviously on a fresh build you have to do an initial adjustment before startup, and cut up a pair of valve covers, but as a confirmation of that adjustment it seems brilliant. Maybe if you go even further you can also find out how much is too much.

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kingbleon85

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I'm trying to set the valves on my mostly stock build. The service manual is too vague. "Tighten the rockers arms while spinning the push rods until they don't, then tighten the rocker arm nut another 3/4 turn." Well, every push rod seems to spin at a different, um, tightness. Does that make sense? Then sometimes that extra 3/4 turn seems TIGHT, then other times it's normal.

Before anyone asks: YES, I soaked the lifters in oil.

Is there a more definitive way to do this?

In case everyone doesn't know by now: 88 RCSB with a 94 5.7L, stock flat tappet cam, and hydraulic flat tappet lifters.
I'm trying to set the valves on my mostly stock build. The service manual is too vague. "Tighten the rockers arms while spinning the push rods until they don't, then tighten the rocker arm nut another 3/4 turn." Well, every push rod seems to spin at a different, um, tightness. Does that make sense? Then sometimes that extra 3/4 turn seems TIGHT, then other times it's normal.

Before anyone asks: YES, I soaked the lifters in oil.

Is there a more definitive way to do this?

In case everyone doesn't know by now: 88 RCSB with a 94 5.7L, stock flat tappet cam, and hydraulic flat tappet lifters.
Tighten the rocker while jiggling the pushrod until you can get no more up and down movement pay close attention because this part is critical, once you feel no more up and down slop between the pushrod and rocker that's what's called "zero lash" then send it down 3/4 turn and move on to next in line.
It's best to start with your #6 set first,you will be able to adjust 8 rockers while #6 is on TDC then spin the crank one full revolution that will put #1 up to fire and you can adjust the rest.
 

1998_K1500_Sub

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People often talk about so many "turns" of the nut...

At the end of the day, it's a length adjustment.

The rocker arm studs I've used had 20 threads per inch. That means there's .050" ( = 1" / 20 ) distance between each thread... so by turning the nut "one turn" it moves .050".

Turn it by 3/4 turn, you've changed it .0375, Turn it a half-turn, it's .025", etc.

I bought some lifters recently with instructions to preload them by .025", so turning one-half turn (1/2 of .050") yielded the proper preload.

OP, your lifter mfgr may have given you a preload spec in inches (e.g., .025"). Or perhaps you might measure the total amount of plunger travel on your lifters and divide it by 2, and set your preload there. (see @Schurkey's remark above "Tighten ALL rocker arms "your choice" of preload. "Your choice" varies depending on the available plunger travel of the lifters--know what you bought!"). In either case, turn the nut an appropriate number of "turns" to yield that distance

If your studs aren't 20 threads per inch, modify the numbers above accordingly (e.g., 24 threads per inch equates to .0417" distance between each thread).

EDIT: See posts which follow for clarification!

:popcorn:
 
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Just Nobody

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I'm trying to set the valves on my mostly stock build. The service manual is too vague. "Tighten the rockers arms while spinning the push rods until they don't, then tighten the rocker arm nut another 3/4 turn." Well, every push rod seems to spin at a different, um, tightness. Does that make sense? Then sometimes that extra 3/4 turn seems TIGHT, then other times it's normal.

Before anyone asks: YES, I soaked the lifters in oil.

Is there a more definitive way to do this?

In case everyone doesn't know by now: 88 RCSB with a 94 5.7L, stock flat tappet cam, and hydraulic flat tappet lifters.
The last one I did,I did it like this.I did head gaskets and its my daily driver.

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PlayingWithTBI

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The rocker arm studs I've used had 20 threads per inch. That means there's .050" ( = 1" / 20 ) distance between each thread... so by turning the nut "one turn" it moves .050".
Yes, the nut moves .050" but, the rockers are 1.5:1 (or 1.6:1) so, the travel on the push rod varies.
 
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