In early January, I installed a rebuilt supercharger from Detroit Tuned (along with a lot of other repairs/refresh) because my original supercharger PTO gears ate each other up from lack of oil due to it leaked out. My car was running great for the next few months, so I was very disappointed to hear a rattle in my engine compartment again. Without diagnosis, I decided it had to be a collapsed timing chain tensioner. I ordered one from FCP Euro, installed it in my garage (I normally work in my shop) and started the engine expecting smooth, quite idling bliss. Nope. I read that it may need a few minutes idling or maybe a brief, easy drive. Nope.

Luckily, I have access to another car, so the Mini just sits in the garage.

So I suspected it had to be a broken timing chain guide. I brought the tools home to pull my valve cover in my garage, but we were expecting temperatures around 115 degrees that weekend, my shop (at work) is air conditioned and I didn't feel 100% comfortable pulling my valve cover without first running the engine with the serpentine belt off - which I didn't want to mess with in my garage. So I had my car towed to my shop.

I got my car on my lift before I left work yesterday and came in this morning ready to open up my engine. I still deemed running the engine without the serpentine belt a mere formality to verify my preconceptions. Serpentine belt off, I went around and started the engine. It idled perfectly smooth and quiet! I was absolutely floored.

I was about to pull the supercharger today but I decided to leave my car in running condition for now (but parked at work) and wait to talk to Detroit Tuned about a warranty claim. Their website states they are out of stock on superchargers right now, so perhaps I'll have to send this one back and wait for it to be rebuilt. I'm not really looking forward to replacing the supercharger again but I do miss driving my Mini as I've been driving my mother-in-law's Honda Civic in the interim.

When I put this supercharger on in January, I also put on a new water pump, belt tensioner, idler pulley, (shorter) belt, colder plugs, ignition coil and wires, thermostat and other seals and gaskets that were convenient while doing this job. I cannot imagine anything else on the belt drive making the box of rocks racket - bad alternators normally whine or grind and A/C compressor on/off has no effect on the noise so...

Yay. I need a beer.

 

The alternator or AC clutch could absolutely sound like a blender full of rocks. Give them a close look.

 

Do you have a mechanic's stethoscope? It's great to pin point that kind of noise. When my alternator went, it was making a terrible noise!

 

Call me skeptical. No A/C problems, no charging problems. Believe me, I would much rather replace an alternator or the A/C compressor than the supercharger.

Prior to my removing the belt, I did use a stethoscope on the timing cover and supercharger. Honestly, the supercharger was louder but I've heard sounds travel through metal before, so I was still in "timing drive fault" mode. Still, it wouldn't be too hard for me to run the engine and get my stethoscope on the compressor and alternator.

I did spin the alternator and compressor clutch as well as I could with the car intact. I also spun the supercharger as well as I could grip the pulley. It could be my imagination or poor grip on the pulley, but the supercharger seemed to have uneven resistance when I tried spinning it. I have a video of my original supercharger on the workbench with me spinning its pulley in a similar manner as I did to the one installed in my car now. The one in my car sounds like my old one on the workbench.

Either way, I'm not sure I could run a shorter belt to bypass the supercharger to run the engine with the accessories (minus the supercharger) being driven.

 

Great video!! I do have a mechanic stethoscope. I will certainly rule out my alternator and A/C compressor. I might not get to it until next Saturday though.

 

To conclude the story, yes, the supercharger was the source of the noise.

Prior to my pulling it, I decided the replace the alternator in a "hail mary" shotgun repair approach to diagnosing my engine noise. I figured, at worst, I'd be replacing a perfectly functioning 161k mile alternator. The old alternator did have noticeable grind feel when I spun the pulley in my hand so I was hopeful this would be the end of the repair, but my optimism was cut short when I started the car and the box of rocks noise persisted.

I pulled the supercharger, sent it back and installed its replacement yesterday. Oh the bliss of starting my car and having it idle without that awful racket!

I was rushed for time yesterday and neglected to fully seat the 2 vacuum pipes in the inlet pipe to the supercharger, so the check engine light came on. I could not reach (by hand or tool) the pipes with the radiator core support in place and the shop was closing in 20 minutes, so I drove it off my lift and parked it outside. I should be driving it home next weekend.