Jason, stick with 1990-1996 Royal Metal Uprights....
For starters, starting in the year 1990, they introduced a new 10-blade metal fan that moves more air than the 6-blade fan does. I guess you could change the fan, but I don't know for certain, & it would require a trip to a repair shop to change it. In addition, the late 1980's Royals saw the start of the brushroll with plastic stiffeners around the brush, which increase the beating action. I have seen an Ebay listing tonight showing an older Royal with this brushroll (versus the older style), but you'll have to shell out more money for it in addition to buying the vacuum.
However, the main reason I say from 1990 to 1996 is they upped the amps to 7 amps, which is the highest available at that time & will provide the same airflow & suction the new 10-amp Screamer Royals that are Chinese-made have now. Also, around 1995 or 1996 (Ben Edge will know FOR SURE what year it was) they changed to a drop-in motor. Prior to this, they used motors that have an oiling port for the rear bearing at the back....if you are looking on Ebay, you will notice a red cap by the rear wheels, this is the cap for the oiling port. You will need to oil the motor once a year with some 10W-30 motor oil....just any generic motor oil will do, no fancy brand needed. I am not certain of the reliability of the drop-in motor, but if I was planning this vacuum to last a long time, I would rather stick with the older motor with a proven track record, if it was me buying this vacuum.
As far as the bagging system goes, that's also another reason to stick to 1990's Royals. That's when they changed to the Style B top-fill bag system. You will see 2 styles of bag available....a zippered bag that can ONLY be used with bags (most common), & on commercial models there is a shake-out bag system. This shake-out bag uses the same top-fill tube as the zippered outer bag, & is emptied by removing the bag from the machine, removing a slide clamp at the top, shaking vigorously, & then emptying into the trash. Since it uses the same tube as the zippered bag, it can be used with the Style B bags if desired. The shake-out bag is made of denim, vs normal fabric for the zippered bag, so it may also be a bit more durable, too, but it's not something I would worry about. There are a few different types of B bags available....standard, micro-filtration, Paper HEPA bags & white HEPA Cloth bags, like Kirby uses, and of course there are generic brands available. This would be a good reason to avoid the earlier zippered bag that uses the A style bags....if you go to use Eureka F&G bags, as that's all that is available now, they are only available in standard & micro-filtration, not the best if you have allergies.
In regards to the height adjustment....I know some people here have said to go with models with the Adjust-O-Rite step-on height adjuster, but I would be reluctant to do so myself. There are only 5 height adjustment settings on it. I have 2 Royal uprights myself, both of which have the Infinite Screw-Adjustment, & that's what I prefer as it allows you to adjust it precisely. If you have only 1 or 2 types of carpet in your home, you should be just fine....simply use the handle lock to put your Royal & roll it from room to room on the rear wheels. My only concern with the Adjust-O-Rite is whether you would be happy with how precise the height adjustment is, but you could always see if your local repair shop will let you take a new Royal home to try out & see if you like it first before buying a model with it.
As for the idea of buying an older model Royal & putting a new outer bag on it, that would be a bad idea. The zippered outer bag is VERY expensive to buy....I was thinking of changing it on my Royal Commercial 670CA, as it uses the shake-out bag & I thought for some reason the zippered bag was larger, I found out it's not larger, though, & a new zippered bag would have cost $125 to buy. If you were to buy an older Royal & put newer parts on it, the best way to go about it would be to find a vac shop that has old used parts in good shape, or find a couple of parts machines. As for the other parts....the belt is the same on ALL the Royals....they all use a Royal Style 8 belt, which is also the same as the Eureka AR canister belt or the Kirby upright belt. The Eureka & Royal belt should be easiest to find in a store, & the Royal belt in particular fits the Dirt Devil Jaguar canisters....they just don't mention on the package, for some reason, that it will also fit the Royal Metal Uprights, too. And if you look at a Royal & Kirby belt, the dimensions are EXACTLY the same & both are knurled....it's obvious they are both outsourced to the same belt company.
If you do follow through with buying a used vacuum, there are 3 items I would purchase immediately for it. 1. A new set of carbon brushes to have on hand....you don't know how hard it was used, & if it's REALLY old, like pre-1985, they could already need to be changed soon after purchase. 2. A new power switch....again, you don't know how much wear & tear the vacuum has, & power switches are a common failure item on vacuums; at least you will have a spare if needed. 3. A new brushroll....just to have on hand when the time for replacement comes around.
Below is a link to a Royal vacuum that shows the newer-style brushroll with the plastic stiffeners, but I am also posting it because it's also a prime example of what you want to AVOID BUYING. This one would just be too old to give a long serviceable life, & isn't worth the money they are asking for it. Also, Jason, if you like, I also have a Adobe PDF document from Royal which has the instructions for oiling the rear bearing....if you, or anybody else for that matter....would like it, simply email me at the email address in my profile.
Best of luck....Rob
http://www.ebay.com/itm/Vintage-Roy...982?pt=LH_DefaultDomain_0&hash=item3f1d44602e
