Supercharger pulley


I have a supercharger pulley that fits too tightly on the shaft of my supercharger, but i haven’t gone and got trained on the lathe yet. Sooooooooo, i was hoping there was someone out there that wouldn’t mind making a little skim cut on the bore of my supercharger pulley so it’ll fit.


If it will fit, but tightly, I wouldn’t use a lathe. Use hone, you’ll be able take off 10ths of thousand at a time until get a nice smooth slip fit. Personally, I would try to keep as much play out of the fit as possible.

Is there any taper on the pulley/shaft. Also, looking at the photo, there are high spots, and honing would take those down.The high spots could cause some problems with the inserts, they don’t like to engage and disengage.

What’s the diameter of the hole, is iy big enough for you to get a boring bar into?


You may try heating it in an oven, & or freezing the shaft if possible. This may be just enough to make it expand to fit.


I’m shooting for a nice smooth slip for like the OEM one, but this one is just small enough that I needed some big beefy pliers to pull it off last time. I really don’t want to have to do that again, so that I can swap pulleys while the blower is still in the car.


Is there a hone at the space somewhere? I need like 3-5 thousands cut from the diameter and it should fit perfectly.


What size is the hole?


As it sits it’s .642, it needs to be .648


Would recommend one of these

BCFlexhone - 18mm seems like it would be the closest. Silicon carbide and 80 grit would be my choices. Seems like it runs about $20.00


Per their instructions, the next size up should be used if it is between sizes. I would suspect if you took it slow you would be good.


Curious on how you measured it. You say it was on there before, Is that correct?

It’s difficult to have a device undersized & removing it with it still being undersized afterwards. Short of heating or freezing it off.


I took 2 measurements with some calipers on the new smaller pulley and 2 on the oem pulley. the oem one slides on and off with minimal force, and is easily done by hand, but the new smaller one took more effort to put on, and significantly more to remove and required the use of tools. If the oem one is anything to go off of then the new smaller one shouldn’t be such a tight fit.


Seems like a good way to go. Gracias señor.


We have gauge pins that will get you extremely close to the correct measurement. Calipers have an inherent inaccuracies even if you are careful.
You may have to take the anodized/paint off the pulley first, even that layer can make a difference.


I thought about using those, but i dont think that this requires much more precision than “yeah, that looks ok i guess”. :stuck_out_tongue:


Yeah, but the difference in fit you are describing sounds like it could be as little as a thou, or maybe even less between the parts.


Thats mostly because i forgot i was talking to machinists. :stuck_out_tongue: I just need a comfy slip fit, and it being 10 or 20 thou bigger than the shaft it lives on wont effect the performance of the blower or cause the belt to fly off or something.



Does anyone want to embiggen my pulley, or do i get to do it backyard/shade tree/sewer mechanic style and tape some sandpaper to a dowel and spin it around in the bore?


Yes, the machinist mentality is telling you how it can be done, you asked us, we answered. But here’s the why is important also.

.010"-.020" oversize is an excessive amount of slop on a pulley under these kind of loads and speeds. That is a LOT of slop for most pulleys on a shaft. Think of all pulleys, gears, etc. you’ve removed froma shaft? They are very close fits. .010" is not a close fit for something on a rotating shaft. You want them as close as possible, snug slip fit is ideal as this prevents any movement/wobble.

Since the shaft is not a tapered fit (or not stated to be one), the slot and key keeps it form rotating, but that does not keep it from moving side to side during rotation and the gap is constantly trying to be moved as the lateral pull keeps changing in relation to any given point. I can’t imagine enough torque being put on the nut/bolt that secures the pulley to the shaft to prevent that.

You will experience premature failure at some point, more than likely causing damage to both the shaft and the pulley, now you’ll have a very expensive repair.

You can use sand paper as you described - it’ll be slow, but when it can just barely fit stop and you’ll be within a couple thousandths.


oh yeah, i wasn’t thinking about the force of the belt pulling the slop out of the pulley. This makes about 1000% more sense now, and i guess i get to go the slow route. Thanks for he help and clarification, i really appreciate it.


And if somehow that pulley was tightened down enough to keep it in place, but 0.010 off center, the tension of the belt changing in total length back and forth by 0.020 repeatedly is quite likely to set up vibration, and likely damage what the pulley is driving.