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Alternator Pulley backed itself off?

27 January 2023
Hey all! Earlier this year I acquired an SOS supercharged NSX (full story here) but ran into an issue this weekend. While out for a spirited drive, I started to hear an intermittent chattering noise that, while downshifting into 2nd gear, suddenly became a constant/aggressive chattering and smelled of burning rubber. I immediately pull over and see my supercharger/alternator belt is shredded on the left hand side.

After limping the car home (was less than a mile away), I noticed the alternator pulley was tilted/angled and rubbing against the supercharger & alternator relocation brackets. With the alternator removed, it looks like the nut holding on the pulley just backed itself off? The alternator is a freshly remanufactured Denso unit from SOS and there's less than 100 miles on the entire build. Curious if this is something I should be concerned about, or if I should just put some loctite and retorque to spec? Any thoughts are welcome. Here's the pulley before pulling off the alternator:

I don't have the SOS supercharger system so I am not familiar with the details of the alternator. However, I think you might now have more than just a loose pulley problem. I thought the regular NSX alternator had a non tapered shaft. If the pulley comes loose it could theoretically walk off the end of the shaft ; but, not cock at an angle like your pulley. A tapered shaft would allow the pulley to angle like your pulley once it came loose which could quickly damage the shaft and or the pulley. Either way, you need to examine the pulley and alternator shaft for damage.

My recollection is that the normal direction of rotation discourages the nut from loosening if it is correctly torqued. No need for thread locking solution. In fact, on any alternator that I have worked on, getting the pulley off has usually required significant effort. If this alternator has less than 100 miles on it, I am thinking somebody forgot to torque the nut during assembly.
Thanks for the input! Makes me feel less extreme for contemplating going and swapping the alternator out with a freshly remanned unit from an auto parts store in case there's any potential hidden damage to the shaft, nut, or pulley. $140 seems like a small price to pay for some insurance and piece of mind.

Will continue to examine the current alternator and setup but may just end up swapping out the unit as a whole.
I am not familiar with the SOS supercharger arrangement. Does it use some Denso off the shelf alternator? If it uses the original NSX alternator, chances of finding a reman are pretty close to zero and even new ones (> $1000) seem to be in very short supply. There are rebuild services that may be able to fix you up.
Hey Old Guy!

The part number on the alternator the SOS kit uses comes back to the same alternator as a 1992 Honda Accord, so definitely much easier to source than the NSX one. After chatting with SOS, however, I learned it's not a 1:1 swap as they do slightly modify the Accord alternator before shipping out (bushing swap mainly from the sounds of it).

The alternator from SOS does not come with a pulley so the group that installed the supercharger kit would have had to remove the pulley from the OE assembly and then put it on the SOS alternator. We think this may be where the breakdown occurred - it's possible that group didn't properly secure/torque the pulley to the alternator before re-installing into the car.

With that said, the SOS team has been phenomenal and working with me to both inspect my existing alternator and we're chatting about solutions of swapping out if needed.
Super common alternator body, though the 80A is probably not.

CJP76 , Used on 1990-1993 Accords.

My car had a CTSC and had no issues.


The NSX alternator seems to have only been used on the NSX. Hard to find and expensive. So don't let it escape your possession. Last I checked the pulley was still available for a nominal price.

It would be nice to know if there are any relatives of the NSX alternator body that can be modified to fit the NSX.