How vanos works

[theimage]

I know basically that the vanos spline gear moves outward to shift slightly the timing of the intake cam. But physically how it can do this mystifies me - maybe someone can explain?

I fail to see how it can work due to two things:
- Cam gear is already fairly snug to the intake cam itself. How would it rotate to modify the timing between exhaust and intake cams?
- The spiral gear on the vanos itself is free to rotate. It seems it would just follow the intake cam, not change the cam's timing / rotation.

I'm installing the vanos and setting the timing now purely by the instructions. I'd feel more comfortable if it made sense how it works even given the two things above. Youtube seems to show the intake cam gear is free to rotate between limits of the grooves on the gear. My cam gear doesn't move freely at all like that.

[kevinwilly]

The vanos DOES spin with the cam, obviously... they are connected.


Basically, when the piston inside moves in or out, the splined shafts in it cause the sprocket with the splined shafts to rotate relative to the other sprocket, which has the main timing chain on it.

The main sprocket is always in sync with the exhaust camshaft and crankshaft. You can rotate the one sprocket with the one turning tool you should have if you are mounting the vanos.

It's been a while since I had a single vanos apart, or I could tell you more. I can explain exactly how a euro double vanos works off the top of my head, though... it's COMPLETELY different from the single vanos systems... which are pieces of crap by comparison.

[theimage]

Awesome, Kevinwilly. You've responded to a couple of my posts recently. I love that sig photo!

I trust that you are correct. Looking at it, I believe the vanos spline gear acts like a physical wedge to force the intake camshaft to rotate relative to the position of the intake cam gear. The vanos spline gear has splines both external (mating to the cam gear) and internal (mating to the cam shaft).

It had sort of perplexed me because the intake cam gear is rotationally snug to the camshaft itself. There is a spring plate for the purpose of making them not totally fixed but again the gear is far from free to rotate after torquing the three nuts to secure everything. But I guess there's enough force from the vanos "wedge spline gear" to make the gear rotate on the cam shaft.

If anyone believes the gear should more freely rotate on the camshaft, I'd like to hear it. I found that a fair amount of force with the exhaust gear rotating tool (on loosened exhaust cam gear) is required (with vanos removed) to cause the intake cam gear to rotate on its shaft.

Cheers.

[RagnarDanskjold]

No free play (at least by hand) on the single vanos units.

It's the force from the plunger piston (large surface area) at engine oil pressure that whips the splined cup axially to and fro.

Rotating around the axis, and with inner and outer splines running in opposite directions, there is a solid rotational connection between all three (outer sprocket, splined cup and splined camshaft insert) and they rotate as one piece.

As the splined cup is extended or retracted, the same mechanical connection exists, but the relative positions of the sprocket and the camshaft are altered by the opposing splines allowing the cup to rotate a distance (radial offset of the external splines) and the camshaft an equal distance in the same direction (internal splines), thus doubling the range for the same given axial offset.

Imagine if the splines on the camshaft were axial, going straight back. Now when the cup extends or retracts, its position relative to the camshaft is the same, but the position relative to the sprocket still changes. Reverse that and put the straight splines on the outside and again, the camshaft rotates in relation to the cup but the cup is stationary in relation to the sprocket. If they twisted in the same direction, they would still function the same, but there would be no offset of camshaft rotation and it would be a useless part. Make them opposing and bam: Vanos.

A little wordy, but long story short, you should not be able to rotate by hand (unless you have the lollypop tool).

[rayesc]

RagnarDanskjold should be a teacher! I'm a visual guy and found this helpful:

Stolen from http://www.bimmerfest.com/forums/att...hmentid=269020


Double vanos is badass:

[Tongboy]

There are some good explanations in this thread - I did a timing chain rebuild on my e39 M5 ~6-8 months back and could NOT get my head around the double VANOS no matter how much I read - the BMW specs & manuals, posts around the forums - but once I actually took everything apart and saw how it moved it all just clicked and made sense - it look SO complicated from the outside but once you see it actually working it will probably make more sense than any amount of reading - unfortunately that means a VANOS rebuild

[Moron95M3]

thank you guys for the pics/info!!! I always understood the idea/theory...but never have seen it yet (haven't done mine yet, although the vert needs it...)
thanks!

[kevinwilly]

FWIW, the last picture is the S54 double vanos, not the standard one. I've been playing with those WAY too much lately.... so sad I know it as soon as I see it, lol....