Background: I have a 15% supercharger pulley on a 2005 R53 at 125k miles. Belt tensioner was replaced at 112k miles at WayMotorWorks when I had some other work done there so it’s good to go.

Recently the idler pulley has been screeching. The drive belt popped off while I was stopped at an intersection. Dash lit up and started to overheat slightly. Shut it off and had it towed home.

Ordered new idler pulley and 15% drive belt from Way. Neighbor has a well-equipped garage and does a lot of wrenching. We followed Mod Mini videos to remove the front wheel, peel back the wheel liner, use the belt tool to insert the pin in the second hole to release pressure on the tensioner, and removed the old belt.

The old belt had not broken but the idler pulley had come loose and was out. Old idler pulley bearings were shot and scrunched together. Hand tightened the new idler pulley and then tightened further to 25 pounds with a torque wrench.

Routed the new belt in the correct order per the videos. Started at the supercharger pulley around to the ATI damper across to the AC compressor up to the alternator and down to the idler pulley. The new belt simply won’t go on to the idler pulley. Seems to be too short.

Two sets of eyes and hands have triple-checked that this is the correct belt size and that the new belt is properly seated in the grooves on each pulley. New belt does seem slightly thicker because of the old being somewhat worn, but that shouldn’t be enough to cause this difficulty.

Here’s the catch: called my local mechanic to describe this. He said to reinstall the old belt and make sure it will go back on. It doesn’t! It also appears too small now.

Suggestions most welcome. Thanks in advance.

 

Is the new idler pulley the same diameter as the old one?

 

Done! Didn't see the other hole for the idler pulley at first from my line of sight at the level the car was raised. Got whine again!
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How did you manage to put it in the wrong hole? Wasn't there a bolt there already?

Related yt link:

 

There was no bolt in the hole after the old pulley literally came loose and out after the bearings seized and the drive belt came off while stopped at a traffic signal.

The bolt is part of the new idler pulley I was installing. Didn't see the other hole for the new idler pulley at first from my line of sight at the level the car was raised.

 

 

Question on the idler pulley install. Does anyone advise lubricating the pulley before install? I am install the idler pulley and the full belt tensioner, so I would like to ensure it is done correctly. Thank you.

 

No need to lubricate, just make sure you have it in the right hole.... : lol (couldn't resist... )