Why We Rebuild and Start Fresh...
I have a lot of customers ask me, why do they need new bearings or new parts in general when we do our port work? I’m going to be answering that question since it seems like there is still a lot of confusion surrounding this topic.
First let’s start by defining the word “rebuild” in this context. To “rebuild” a supercharger means to change all the bearings, fluids, and possibly some gaskets if needed.
If we break down the design of a bearing, we have a center ring or cylinder that rotates around inside a set of round balls or cylinders that are also rotating. Those all rotate around inside a larger ring or cylinder that stays static. That's a bearing in the application I’ll be discussing here. The center moves, the outside does not.
So next we have these pairs of rotors and they have two bearings in the blower case for each rotor, and each one has its job. That is to keep the rotor centered and let it spin. So here we have a single bearing on both ends of each rotor asked to spin very fast…… Let's do the math.
First we’ll need to determine the pulley ratio. The lower/ crank pulley is divided by the upper/ blower pulley and that gives you the pulley ratio. Let’s say 7.50 inch diameter for the crank pulley and 3.0 diameter for the stock blower pulley. This gives you 2.50 for your pulley ratio.
Crank pulley / Blower Pulley = Pulley
7.50 / 3.0 = 2.50
Now that we know the pulley ratio, we can calculate the blower speed in which it’s rotating. Say we spin the engine to 6500 RPMs. So now we take 6500 times the pulley ratio of 2.50 and we get 16,250 blower RPMs.
RPM x PULLEY = Blower Speed
6500 x 2.50 = 16,250
Now let's take this up a notch. We have a lower pulley of 8.25 and an upper pulley of 2.45. The ratio is now 3.36. So now we take that 3.36 and multiply it by 6500, we get 21,887. Wow, we really turned it up. This blower is now spinning 22K RPM. This is a lot of force on those bearings to be spinning 22 thousand times in a minute.
(8.25 / 2.45)6500 = 21,887
So knowing your supercharger is being spun to 22 to 26 thousand RPM’s, this is a big deal. If you actually look up some of the bearings used from the OEM in their catalog, you will find that the bearings are not even rated for the speed in which you are trying to make them spin, let alone last because god forbid your blower has any issues when you ask it to make 950 wheel and more. LOL
When a blower shows up at our shop for porting, we have to remember these things. Everything gets taken apart to the bare bones. Every bearing is right there, taken out of the case or snout. Unfortunately, the only way to remove the bearings is to break them, so they become un-reusable. Then the case or snout is put in the CNC or maybe it's done by hand. Either way, we have all this aluminum shavings and even coolant spray from the CNC getting all over it. These bearings were never made to resist any type of liquid or debris in them which is why we remove them. In a CNC or a wash tank, they would be totally subjected to fluids and debris constantly or even a high temperature, so the functionality of them after that exposure would be questionable.
This also applies to brand new blowers. I also get the question of do I really need brand new bearings if it’s a brand new blower? The answer is yes, because it’s the same process for a new blower as it is for a used one. Those bearings would be far from brand new after if left on.
So knowing your bearings would go through all of this, will you even question the thought of doing new bearings? The answer should be no. Never have I done a supercharger porting without doing new bearings. The time it takes me to tear one down, port it, then assemble it compared to the little time it takes to remove bearings and install them, why wouldn’t I do that too? To save 40-100 bucks, am I crazy? It's open and right there, and there is minuscule labor cost involved. You've spent the money on a badass port, but you skimp on the essentials? I don't think so. Why risk having it seize up and cost even more to fix?
Your takeaway from this should be this: take this seriously. I know cost is always a factor, but you know what costs more? Having to do it two or three times when it wasn't right the first time. This will cost you more money than you know, let alone the time and frustration. Don't get me wrong, new bearings can also fail. I can admit there have been times where I have put a new bearing or part into a supercharger and it just failed right from the start. It can happen, but I would rather take the lower chance of that happening, than the higher chance of failure with reusing all the bearings. Trust me when I say, your build is worth it…..