Testing VIS causes rattle

[SteveThackery]

Sorry, I seem to be hogging this forum recently.

I tested my newly fitted VIS motors today by earthing the direction pin in each connector.

Without the engine running both motors run quickly and smoothly to their "activated" positions, and back again when the earth is removed, exactly like in this video:

https://youtu.be/_2YwfQuzvDc

Out of curiosity I decided to repeat the test with the engine running. The balance valve makes no difference, but when the power VIS is actuated there is a harsh rattle from the manifold chamber. The rattle is only when the engine is running and the power valve actuated. It gets louder and faster when the engine is revved. Releasing the power valve makes the noise stop immediately. My first guess is that the intake air pulses from the engine are making the flap valves rattle when they are open, but not then they are closed. The brown plastic lever for the valves slides smoothly from left to right, and has no obvious sideways play in either plane.

Obviously I've searched the forum, but all I can find are reports of rattling at idle without manually operating the power VIS motor.

Has anyone done this experiment on their own car? Actuating the VIS motors when the engine is running?

[stocktake]

The cup and cone joints that connect the brown arm to the 6 flaps are worn i'm afraid. replacement of the manifold is the only cure i'm sorry to say

[SteveThackery]

Doing a bit more research, it seems that the noise will be due to play in the various knuckle joints connecting the flaps to the actuating lever.

My guess is that with the power valves closed (where the flaps are pulled closed against their stops) the pull from the actuating lever takes up any play in the knuckle joints. In the actuated position the flaps are in line with the air stream and no longer forced against a physical stop, so there is nothing to take up the play in the knuckle joints. That play means the flaps can flutter in the air stream, making the knuckle joints rattle.

Presumably the play (and rattle) will get worse as the knuckle joints wear, until one of them falls apart. At that point there will be one uncontrolled flap, and the rest of the mechanism will either continue working or jam. If the VIS motor tries to move a jammed mechanism, I can imagine it could break some part of it.

The variable intake system is a good thing, but I think it was a terrible decision to make it a sealed, non-serviceable unit. Terrible for us, that is. BMW/Rover just needed it to last a decent interval past the warranty period.

How can I mark this thread <SOLVED>?

[SteveThackery]

Originally Posted by stocktake

The cup and cone joints that connect the brown arm to the 6 flaps are worn i'm afraid. replacement of the manifold is the only cure i'm sorry to say

Oops, you beat me to it!

It occurs to me that the power valves only actuate at large throttle openings and high rpms, so for the great majority of the time they should remain closed against their stops, with no wear taking place. That makes me think they could still last for a long time. Do you agree?

[SteveThackery]

Does anyone have a scrap inlet manifold chamber I could have, to experiment with?

Obviously I'd be happy to pay all the shipping costs, plus enough for several beers.

[stocktake]

Originally Posted by SteveThackery

Oops, you beat me to it!

It occurs to me that the power valves only actuate at large throttle openings and high rpms, so for the great majority of the time they should remain closed against their stops, with no wear taking place. That makes me think they could still last for a long time. Do you agree?

You will have no Vis movement at all until you apply over 31% throttle, once that criteria has been met things start to happen around 3000 rpm, there is a graph somewhere on here that shows the subsequent Vis operation.

However, both balance flap and power butterflies are open at rest. (despite some so called "experts" of facebook pretending they know the operation. )

So, if you do have wear, the butterflies will be held in place by the cup and cone joints only and the stop. the flaps ill not be supported by the seating surfaces but held in mid air in the open position.

The manifold when you look at it looks very easy to open with a series of bolts holding a cover plate on. This is not the case, having removed the case bolts you will find the casing is what appears to be ultrasonically sealed and opening without damage is quite difficult.

I do have a worn out inlet manifold (somewhere) that I butchered to open up you are free to have this for the price of postage I will find out the cost this week. PM me your address.

Link for vis operation
https://the75andztclub.co.uk/forum/s...91&postcount=6

[SD1too]

Originally Posted by SteveThackery

It occurs to me that the power valves only actuate at large throttle openings and high rpm ...

Just a note on this which I discovered years ago when helping to trace a fault on a ZT-T in the presence of T4.

The power valves react to fast and large changes of throttle position. For example, if you emerge from a side road into a gap in high speed traffic and, having executed the turn at a safe, controlled speed, floor the accelerator pedal in order to match the flow of existing traffic, the power valves will respond and the car will surprise you by picking up its skirt and sending the tachometer flying up towards 6,000 rpm!

Simon

[SteveThackery]

Originally Posted by stocktake

However, both balance flap and power butterflies are open at rest. (despite some so called "experts" of facebook pretending they know the operation. )

Now this is most interesting. To be fair to these "experts", they are only quoting the Technical Brochure, a screenshot of which is attached.

https://www.dropbox.com/scl/fi/k3oxc...sung-Notes.jpg

That says the exact opposite, which is very interesting and confusing!

[SteveThackery]

Originally Posted by stocktake

.

I do have a worn out inlet manifold (somewhere) that I butchered to open up you are free to have this for the price of postage I will find out the cost this week. PM me your address.

That would be great, thank you. I'm also hoping to get hold of a scrap (defective) one which has not been opened. One of those, plus yours, would be a great combination. I'll put out a request on the forum, and I will PM you my private address.

Thanks, stocktake - you are being very generous.

[SD1too]

Originally Posted by SteveThackery

https://www.dropbox.com/scl/fi/k3oxc...sung-Notes.jpg

That says the exact opposite, which is very interesting and confusing!

Steve,

Unfortunately your link cannot be viewed without creating an account. However, we are aware of RAVE's description of the VIS system and I can confirm that what Dave (Stocktake) has said is correct as you are no doubt about to find out for yourself!

Simon