Correctly setting valve lash.

[Orpedcrow]

For added confusion, the cam/lifter/pushrod “kit” I put in my Harley, wanted me to count the flats on the nuts as I adjusted them.

I was taught the EOIC method in school many years ago, but that takes a bunch of time and a bunch of thinking (for me) but it also works.

 

[1998_K1500_Sub]

Yes, the nut moves .050" but, the rockers are 1.5:1 (or 1.6:1) so, the travel on the push rod varies.

Good clarification... moving the nut down (essentially moving "the rocker fulcrum" down) by, say, .025" will move the pushrod down a different (greater) amount based on the (1) lengths of the rocker on either side of the fulcrum and (2) the angle formed between (a) the stud and a (b) line through the rocker arm's point(s) of action (on the valve and the pushrod).

Somebody wanna work this out? I gotta go to lunch...

EDIT: More on this in the following posts...

 

[PlayingWithTBI]

Somebody wanna work this out? I gotta go to lunch...

Just multiply 1.5 (or 1.6) X .050 (or whatever TPI X # turns) = actual travel... I think

 

[1998_K1500_Sub]

Just multiply 1.5 (or 1.6) X .050 (or whatever TPI X # turns) = actual travel... I think

We’ll, it’s not EXACTLY that simple, and the angle of the pushrod/lifter to the rocker has an effect too which I overlooked earlier.

But roughly it’s = (1 + ratio) / (ratio), so for your example

= (1 + 1.5) / 1.5

= 1.67

But you’re probably close enough.

 

[PlayingWithTBI]

But you’re probably close enough.

I'm just going by how total lift is calculated on a cam. You take measured lift on cam times rocker ratio = total lift. I would think that would be pretty much the same with lifter "Preload"

 

[1998_K1500_Sub]

I'm just going by how total lift is calculated on a cam. You take measured lift on cam times rocker ratio = total lift. I would think that would be pretty much the same with lifter "Preload"

Yeah, I see where you're coming from. It is indeed different though, when tightening the nut to set the lash/preload; the "valve end" of the rocker is actually the fulcrum, and as the nut is tightened the "pushrod end" moves down a greater amount than the nut.

During engine operation, the nut is the fulcrum.

So a rocker geometry that gives you 1.5:1 valve-to-pushrod action will have (1 + 1.5) / (1.5) = 1.67:1 pushrod-to-nut action.

Even both of those are approximations -- a "1.5" rocker ratio is only nominal -- because the rest of the valvetrain geometry comes into play throughout the motion of the components. The reason: They're not all parallel... the valves point in one direction, the studs in another, and the pushrod/lifters a third... at least, on a Pontiac engine they do. I went down this "rabbit hole of learning" last year when I needed to select the proper pushrod length for my roller-cammed 455.

I did get the pushrod length correct, after monkeying around with a set of low-tension springs on the valves and studying the effect of changing pushrod length on the action of the rocker and the valve through the entire range of motion. Things happened that I didn't expect, although in hindsight it was obvious. Call me naive; it was "baby's first engine".

And evidently I over-set the lifter preload on the 455 because I didn't take into account the leverage effect of the rocker on the pushrod. DUH!

So I learned something today.

I ain't too old to learn... but it does take a little longer

 

[1998_K1500_Sub]

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!

@Schurkey, this is as simple as I've ever seen it described.

I'm trying to wrap my head around (a) why this method works and (b) why I've never seen it practiced.

Is there an unstated assumption / requirement / fact, here, that at least half the valves are on the base circle of the cam, regardless of camshaft orientation?

 

[Schurkey]

BUT WAIT! THERE'S MORE!

Let's really confuse the OP.

There's the philosophical debate on setting lifter preload. Let's take a theoretical lifter that has plunger travel of 0.200. ACTUAL plunger travel of YOUR lifters may be different--anywhere from single-digit thousandths (.008, as an example) to more than a quarter-inch.

Point is, SOME guys want very little preload, .025 or maybe less, so the lifter can't "pump up" at high RPM and keep the valve open. With the plunger near the top of it's travel, there's very little compensation for wear at the cam lobe, lifter bottom, or rocker arm.

SOME guys want the lifter plunger somewhere in the middle of it's travel, around .100, which is what the OEMs tend to suggest. If the valve seat or valve face--or both--wear, the plunger has room to adjust lower in the lifter to make-up for the wear. If pretty-much anything else in the valvetrain wears, the plunger in the lifter has room to adjust higher in the lifter to compensate for that wear.

A FEW guys want the lifter plunger nearly bottomed-out, somewhere around .175 or deeper, so the plunger can't bleed-down and reduce valve opening when used with stiff valve springs. With the lifter nearly collapsed, there's very little compensation for wear at the valve seat/valve face.

Which is why the reduced-plunger-travel lifters became popular with hot-roddy and high-horsepower types. With only a few thousandths of plunger travel, the plunger is simultaneously near the top of it's travel, AND near the bottom of it's travel, allowing almost no pump-up, and not allowing plunger collapse when used with stiff valve springs to alter the valve adjustment much. Problem is, there's almost no compensation for valvetrain wear.






On a stock- or mostly-stock engine, in normal service, I'd want whatever the factory spec for preload is--assuming the lifters have stock amount of lifter-plunger travel. I wouldn't be buying the severely-restricted-travel lifters.

@Schurkey, this is as simple as I've ever seen it described.

Yup. It don't get any easier that that.

I'm trying to wrap my head around (a) why this method works and (b) why I've never seen it written down.

Is there an unstated assumption / requirement / fact, here, that at least half the valves are on the base circle of the cam, regardless of camshaft orientation?

Yes. At least half the lifters are on the base circle no matter what position the cam is in. Any camshaft that has less than 360 degrees of advertised duration-plus-clearance ramps will suit this procedure. So perhaps a maximum of 320 degrees of advertised duration, with 20 degrees of clearance ramps on the intake and exhaust lobes.

Put another way, virtually all hydraulic cams have 360+ degrees of base-circle. Remember, a full turn of the cam is 720 degrees.

For the record, I shamelessly stole this method from a guy with username "Motordaddy" on another forum.

 

[tayto]

for stock stuff you can use these simplified method but anything not stock i use the exhaust opening, intake closing method

 

[DeCaff2007]

for stock stuff you can use these simplified method but anything not stock i use the exhaust opening, intake closing method

Yet another reason for a stock build.