Quote:
Originally Posted by andrewwynn
Rattle rings? Are those the sets of "recatarings" that seal the oil distribution units?
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They're called rattle rings because they fix a problem that causes a rattling noise in the VANOS.
In each VANOS piston, there is a Steel ring with about a 7mm square cross section, about 35mm diameter. Over time, the moving parts within this ring (needle bearing discs and washers) wear slightly, allowing for some extra slop which makes noise and somehow interferes with the timing adjustment. So the fix is to swap those "rattle rings" with ones that are slightly thinner. On mine, the new ones were 0.12 mm thinner. This means that the needle bearings and washers in the middle are now loaded again, so they don't rattle around.
Also, on the question about how exactly does the VANOS change the timing ... there is probably tons of carefully considered info out there on the interwebs, but here's my take from looking at the system recently:
The solenoids meter oil pressure to each of the VANOS actuators - one on each camshaft. So somehow the solenoid lets in the right amount of oil (at system oil pressure) to cause the VANOS pistons to move to the desired position - the pistons are aligned with the camshafts.
Each of those pistons move a little cup thing with TWO sets of helical splines - one on the inside of the cup, one on the outside, and since the two sets are rotating in opposite directions, when the piston moves in or out, it causes a rotational displacement between the pulley (connected to the outer helical splines) and the camshaft (connected to the inner helical splines). So mechanically, that's how the system can get whatever timing shift it wants, continuously.
The primary timing chain runs from the crank chain pulley, rigidly attached to the crankshaft ... to the exhaust camshaft's timing chain pulley ... then the exhaust VANOS makes its angular offset adjustment vs. the exhaust camshaft. The exhaust camshaft also has a secondary chain that drives the intake camshaft timing chain pulley. There, the intake VANOS dials in whatever timing adjustment it wants between that pulley and the intake camshaft.
So this way, in summary, those solenoids control oil flow to the VANOS. The VANOS moves its pistons, which move those double helical cups, which cause the camshafts to adjust their angle with respect to the pulleys. Continuously variable, independent on intake and exhaust. Pretty effin' amazing to see it all there and knowing it works so well.