[dre_2ooo]

In a traditional (DOHC) piston engine, the cam lobes move the lifters which then push the valve stem.

In valvetronic, the valves are directly pushed by a couple arms. The arms' positions change the valve opening. The cam lobes push directly on these arms. There appears to be no need for lifters anymore..

Valvetronic animation:

Be nice....

[dre_2ooo]

Before anyone says it:

They tick.

[dre_2ooo]

Originally Posted by TrackRat

Not quite correct...

The cam lobe pushes on the lifter which pushes on the pusrod which pushes on the rocker arm which pushes on the valve stem.

I mean on a typical DOHC engine. Like this:

[timmahh]

Originally Posted by dre_2ooo

I mean on a typical DOHC engine. Like this:

That's the lifter setup I believe, same method used on the Nissan KA24DE, however other cars like my first one ever.. pos ford probe.. had a single cam in the middle with rocker arms above the cam shaft that reacted to the cam profile. BMW looks to use a rocker-arm type method but it's not the same as what older or basic engines use, and thankfully they don't use pushrods!

[mike-y]

That video shows a 'bucket' style lifter that i've seen in some nissans and VW's. the dohc honda engines i've worked on have a more traditional rocker arm "follower" that rides under the cam lobe and pushes down on the valve stem.

IIRC, the bucket style required shims to adjust clearance, where as the rocker arm style had an adjustment screw, which was much easier to adjust.

And regarding pushrods, they are not all bad. The newer LSx enines are all pushrod engines and are extrememly compact and lightweight, especially when you consider their power output. When done right, a pushrod engine has its advantages.

[bsamoul]

Originally Posted by dre_2ooo

Before anyone says it:

They tick.

That's exactly what they do

[timmahh]

Originally Posted by mike-y

That video shows a 'bucket' style lifter that i've seen in some nissans and VW's. the dohc honda engines i've worked on have a more traditional rocker arm "follower" that rides under the cam lobe and pushes down on the valve stem.

IIRC, the bucket style required shims to adjust clearance, where as the rocker arm style had an adjustment screw, which was much easier to adjust.

And regarding pushrods, they are not all bad. The newer LSx enines are all pushrod engines and are extrememly compact and lightweight, especially when you consider their power output. When done right, a pushrod engine has its advantages.

ah! Bucket style, couldn't quite figure out the correct terminology thank you

[Bimmer This]

Originally Posted by TrackRat

Not quite correct...

Typically the cam lobe pushes on the lifter which pushes on the pushrod which pushes on the rocker arm which pushes on the valve stem, in "pushrod" engines. You can also have the cam lobe push directly on the "lifter" on overhead cam designs.You can also have rockers that work directly off the cam without pushrods or traditional lifters. You can also have hydraulic "lifters" built into the ends of rocker arms. There are many different variations possible. Valvetronic changes the valve lift by altering the rocker arm "follower", pivot.

this!

[hipnotic]

lol

[dre_2ooo]

I still don't see what purpose they serve in the N52/N54....

The rocker arm pushes the valve and it is pushed by the valvetronic arm. the valvetronic arm is pushed by the cam lobe. What do the lifters do??

[dre_2ooo]

No one knows for sure?

[mike-y]

You should note that you added a link in your original post, that shows the N52. The new video shows a completely different type of valvetrain than the first, which was a generic dohc design with lifters. Not so on the N52. It's a completely different design and doesn't use a traditional lifter like the other video you have. There is really no discussion here. What are you calling the lifter on the N52?

[dre_2ooo]

#7. It looks like it counteracts the effect of the valve spring... which seems pointless.

[GenePoole]

"Lifter" is a carryover from the old days when they rode against the cam and actually transmitted the movement from the cam lobe to the rest of the valve train. "Tappet" is more accurate and covers older lifters as well as indirectly coupled units like the ones in the BMW. They have a hydraulic "cushion" internally that absorbs slack when the cam lobe is moving on its downward stroke.

[dre_2ooo]

So it looks like they are opposite of the valve stem and they cushion the 'backlash' of the valve spring when the valve closes...

[dre_2ooo]

so...?

[GenePoole]

So... I don't know what you're digging for? Should I explain the fundamentals? Basic thermodynamics necessitates that there be some clearance to allow for heating/cooling therefore without a hydraulic buffer (i.e. in the case of solid lifters) you'll get an annoying pecking noise from the valve train.

[dre_2ooo]

Originally Posted by GenePoole

So... I don't know what you're digging for? Should I explain the fundamentals? Basic thermodynamics necessitates that there be some clearance to allow for heating/cooling therefore without a hydraulic buffer (i.e. in the case of solid lifters) you'll get an annoying pecking noise from the valve train.

Is this necessary even if the rocker arm is in constant contact with the valvetronic arm? I get why cars have hydraulic lifters... I just don't see their place in valvetronic.

[GenePoole]

It isn't in constant contact. That's the point. For the valve to seal completely, there must be some play in the valve train (when the cam is "off" the lobe) so the spring can hold the valve tightly shut.

[dre_2ooo]

I just don't get how that keeps the valvetronic arm in zero clearance with the rocker arm. All I can see it doing it keeping the rocker arm in constant contact with the valve stem. I guess I'll never understand it.

[Killer]

Just wanted to say that this certainly wasn't a dumb question. I've been wondering the same thing myself, particularly since in all of the Valvetronic demonstration videos I've seen, the hydraulic "lifter" appears to me to remain completely stationary. Thanks, GenePoole, for your explanation(s). Makes perfect sense now.