One of the water pump screws fell down and into the bottom wheel of the tensioner. Now I can hear it inside scrapping against the metal. It does not look like a good place to stay. However, the entire back of the wheel is encased in plastic. The only hole appears at the top where it fell into. Now it is stuck inside of the tensioner.
What a nightmare.
Is it possible to remove the bottom wheel of the tensioner to get it out? If so, why aren't people doing this all the time because it would make the bolts 100% more accessible to the water pump to not have that entire bottom of the tension wheel in the way.
I "believe" the axle is only held in with a star bolt and nut but are there magic springs in there. What is the torque to put it back?

 

What you are referring to is neither called, nor does it work as a tensioner. It is the friction wheel pulley (made of metal), held by its actuator (the piece in plastic). The entire part (plastic assembly and metal pulley) is called the friction wheel. Depending on the target market of the car, it enables the car to selectively (or permanently) drive the water pump. The actual tensioner is what you had to move to its service position in order to replace the serpetine belt.
For clarity's sake, please do not refer to the friction wheel as "tensioner".

Yes. Only this one is self-made. (sorry, I couldn't resist :-) )

It is possible to remove the friction wheel pulley (Peugeot/Citroen and european aftermarket part sellers sell the pulley by itself - unlike BMW/MINI - in case its bearing has failed but the rest of the friction wheel is in order). BMW/MINI instructions for the removal of the water pump even list removing the friction wheel as a preliminary task for removing the water pump (though replacing the water pump can be done without touching the friction wheel). Once the friction wheel is off, the screw will fall out without the need to remove the friction wheel pulley from it (the metal pulley is "open" on the engine side).

No. The specified torque for the three screws holding the friction wheel (the plastic part) to the engine is 9 Nm.

Now for the bad news:
Removing the friction wheel is unfortunately a cursing inducing job. I wasn't able to access the top screw without placing a hydraulic jack under the engine, removing the right engine mount (and everything needed prior to that) and then lowering/rasing the engine in order to access that screw. This was despite having the "special tools" (low profile WERA 8790 FA 10mm socket and a slim, 11mm, flexible ratcheting wrench to drive the socket) listed in the BMW/MINI instructions for the job. However, I have seen reports by people who have done it without raising/lowering the engine.

Here's the BMW instructions for getting the friction wheel out.

 

PS.: Do not forget to put the friction wheel back into regular operating mode (last picture in the instructions attached above)! Doing so and starting the engine will cause the engine to overheat without giving any warning or throwing a code until it is almost too late!

 

I am not talking about taking the whole friction wheel off. I'm only talking about taking the bottom pulley out which looks like it is held in with a single screw and nut easily accessible. The thing I'm not sure about is if the metal pulley has enough room to slide out the back.

Also, the whole pulley is not open to the back. That is the issue. It only has a small opening "at the top" which is where the bolt fell into. I have ordered some magnets and and flexible magnet so I'm going to try that first.

 

For those friction wheels fitted at the factory (made by DAYCO), it is not possible to take the pulley off, without first removing the friction wheel as a whole from the engine. Even if you remove the bolt, the screw will remain in place, holding the wheel back. And the only way to remove the screw is by pulling it out from the other side.

FWIW:
The pulley _is_ open on one side. Search for images of "R56 friction wheel" and look closely at those showing the friction wheel assembly from the inside (i.e. the side towards the engine). It may help when trying to use the magnets. Good luck.

Edit:
Some pictures on the net show the screw to be accessible from the outside and the bolt from the insde. If yours is that way and you manage to keep the bolt on the insde from spinning, the screw may come out and free the pulley.

 

Mine has a nut on the inside and a torx screw with "key" on the outside. It looks like if I held the nut inside and turned the screw outside, the nut would eventually fall off. Maybe you are saying the screw is really going inside of collar with threads inside the collar?

There is a "tiny hole" in the back. Which is about the size necessary to accept and envelope the bolt from the water pump. I am not sure I can even squeeze the whole pulley out that hole. So if I removed the screw, I would need the whole tensioner pulley to fall off of the rest of the tensioner.

I bought this from Amazon I am hoping I can get up in there from the rear and get it out. . I can through wire through the hole and bind the magnet and then bend it to go up and get it. I hope one of those things works.

 

Well the amazon flexible parts magnet was a bust. That thing is way, way too big. This isn't looking good.

 

Maybe you can blow it out with compressed air? Maybe compressed air in conjunction with a magnetic retrieval tool?

 

I don't think it is going to move with compressed air. However, I have contemplated vacuum.. lol

I am wondering if I could get a tiny vacuum hose in there?

 

One of these small magnets https://jc-magnetics.com/Magnet-N52-...untersunk-Ring attached to a piece of wire and I was able to retrieve the screw without further teardown.

Thanks for the help. I am glad I was able to avoid a nightmare. All bolts in positioned now and ready to start tightening.