S54 Diaphragm Springs and Exhaust Hub

[bmwfnatic]

Question on the VAC hub. Is there a point where there is too much play due to a worn pump disc for this to be a good solution? My assumption is this hub is designed for a used OE disc, not a brand new set of holes at OE or smaller diameter. I bring this up because I talked to Beisan last week and she asked why I didn’t order a disc and I explained I got the VAC hub and was told it will eventually hammer the worn disc holes further leading to a code. I’m not entirely sure I buy that, but I’m also not sure it's an impossibility.

I think it makes sense, if the holes are already elongated and aren’t really the original size anymore, then the VAC hub won’t have the play they intended it to have, could see where they are coming from.

However if your holes are pretty much undamaged, I think it will be fine.

[maupineda]

When I installed mine, VAC hub on a brand new Vanos unit the play was the same as the redrilled smaller holes versus the OE hub.

either solution is just as effective as you want the reduced play.

I should have measurements on both setups. Will see if I can find them.

[sapote]

Question on the VAC hub. Is there a point where there is too much play due to a worn pump disc for this to be a good solution? My assumption is this hub is designed for a used OE disc, not a brand new set of holes at OE or smaller diameter. I bring this up because I talked to Beisan last week and she asked why I didn’t order a disc and I explained I got the VAC hub and was told it will eventually hammer the worn disc holes further leading to a code. I’m not entirely sure I buy that, but I’m also not sure it's an impossibility.

Check your disk holes or post the pics here. Most of the time I think the VAC driving pins should fit well with even a used disk.

[chris719]

Question on the VAC hub. Is there a point where there is too much play due to a worn pump disc for this to be a good solution? My assumption is this hub is designed for a used OE disc, not a brand new set of holes at OE or smaller diameter. I bring this up because I talked to Beisan last week and she asked why I didn’t order a disc and I explained I got the VAC hub and was told it will eventually hammer the worn disc holes further leading to a code. I’m not entirely sure I buy that, but I’m also not sure it's an impossibility.

[George Hill]

Untouched S54 in a 94k mile Z3M

[sapote]

Sapote, the spring does not compress any more beyond the installation point, the hubs bottom out on the cam sleeves, so they cannot travel any forward. Take one apart and you see all the surfaces that are in contact.

During operation the spring continues being released/compressed within a limited range as the vanos piston moving forth/aft.

The hub is bolted to the thrust bearing ring (rear of the sprocket on the rear side of the wall.So the hub, sprocket, and the thrust bearing can move forth/aft relative to the head as this gap plays is required in order for them to rotate relative to the head. During vanos closed loop control opearation, the plays of this gap must be minimized to avoid control loop oscillation and this is the reason for the spring plate.

So during operation, the hub pressing/releasing on the spring as the vanos piston moving back/forth.
The hub bottoms out on the sprocket/thrust bearing but not on the cam sleeve. The gap between the hub and the sleeve is changing based on the how strong the spring. If the hub is bottomed on the sleeve then there is no need for the spring.

[maupineda]

Sapote, the spring does not compress any more beyond the installation point, the hubs bottom out on the cam sleeves, so they cannot travel any forward. Take one apart and you see all the surfaces that are in contact.

[sapote]

Hmm, not sure I follow. If the I6 cam needs more force to get moving with no springs, wouldn't you want a weaker spring so that's it's at the same static torque than the V8 cam with a stiffer spring?

Imagine without the spring plate situation:
I6 needs more linnear (forth/aft) from the vanos piston to turn the cam
V8 4-cylinder cam needs less vanos force to turn the cam.
Are we all agree?
Why do we need the spring plate? There is a gap (due to manufacturing) between vanos hub and the cam sleeve as they rotate relative to each other during timing variation. we don't want the gap as this can cause oscillation (rattle) in operation, and so a spring plate is installed to preload or take out the gap. The spring plate should be strong enough that the vanos piston can't compress it or compresses an insignificant amount. This means the spring force should be selected to be larger than the vanos piston force needed.

Therefore the spring for S54 should be stronger than the one for V8. So I don't understand why the S62 'B' spring is stronger than 'A" or S54 spring.
Unless the S62 requires faster acceleration than the S54, then the vanos force of S62 is higher which requires stronger spring plate.

[heinzboehmer]

If this is true then they should use a weaker spring in the V8.
The spring is used in between the splined hub and the cam to minimize the plays between the twos. More plays causes vanos oscillation (it's a closed loop position control)
I6 cam needs more linear force to turn, means more compression force on spring.
V8 cam needs less. This means V8 can use weaker spring, unless the V8 has faster cam variable timing than S54.

Hmm, not sure I follow. If the I6 cam needs more force to get moving with no springs, wouldn't you want a weaker spring so that's it's at the same static torque than the V8 cam with a stiffer spring?

[sapote]

Also look at it this way, even if the end conclusion is that there's (virtually) no difference in performance between the "A" and "B" springs, that just means that no one should care to remove their existing S62 springs.

Stronger spring slows down the variable timing, and more wear on components, even if not observable, but measurable.

[sapote]

I feel like Raj @Beisan Systems was the one who came up with this idea. What is this supposed to fix?

I thought it was used to fix vanos rattle. If we don't know why then why many owners used S62 springs?

[sapote]

So maybe they started with the same I6 spring constant on the V8 and then realized that they could get away with a higher spring constant because of the reduced friction of the shorter cams. S54 still has the longer cams, so they kept the original springs there.

If this is true then they should use a weaker spring in the V8.
The spring is used in between the splined hub and the cam to minimize the plays between the twos. More plays causes vanos oscillation (it's a closed loop position control)
I6 cam needs more linear force to turn, means more compression force on spring.
V8 cam needs less. This means V8 can use weaker spring, unless the V8 has faster cam variable timing than S54.

[sapote]

I had a client stop by today and I ran the Vanos test on his car. I don't have a before, but I do have an after. His car got everything plus the rattle kits for the splined shafts. These two tests span about 30k miles.

2020:




2024:

This car shows the advancing takes much more time then retarding.

While the previous car with EX advancing is quicker than Retarding which is odd, below. The only way to explain this is the engine rpm was dropping (decelerating) during the vanos movement.

[maupineda]

To be honest, I don't think used parts would see wear, thermal cycling would drive minimal expansion, these parts are heat treated so they are very resilient. that is why the idea that they wear and start to make noise have no fundamentals. they would need to go flat to not provide the preload needed for smooth operation. but do the math, the amount of force needed to compress A v B to its installed state is twice as much, so that is added drag that is completely unnecessary. I mean we are a community we change parts to improve the car, this just goes against that principle, even if the effect is minimal, is a step back, not forth. it is cool to see threads where we put data up for discussion.

[George Hill]

Throw a used set in a parts washer. They'll look brand new

I just wonder if they lose tension over time, maybe not enough to matter but its worth considering all options if I'm trying to make an honest comparison. I don't want to do this twice, lol