I have been asked why I use bushed pulleys. Aren’t they just another expense? Bushes pulleys, as far as I’m concerned, are an important part of KISS engineering. A bushed pulley is something that can be used on a range of shaft sizes. I use the SK sized bushing because it covers the range of sizes we DIYers normally find ourselves involved with. There are a few using the 48mm shafts, and the SK bushing covers this rather large size as well. If we step up one size to the SF bushing, we can even cover a 2 inch bore, which is the size of the Lister 6/1 crankshaft!
Bushed pulleys allow us to attach a pulley to a shaft with a VERY positive fit, if you do it right, it’ll never slip, it’ll never come loose, you won’t mangle a key way, and you can remove the pulley in sub zero weather with gloves on! Standard bushings have two sets of holes in them; one can be used as ‘pass throughs’ and the others are threaded. What you need to know BEFORE you install a bushed pulley is that one set of these holes is used as JACKS to jack the bushing back out of the pulley. This is typically done when the pulley is put on the shaft first, with the widest part of the hole facing the end of the shaft. Then you fit the SPLIT tapered bushing onto the shaft with the smaller end first.
Some folks new to tapered bushing can’t get the new bushing on. If you are experiencing this, always check the shaft and the bushing to make sure they are the same size. Once you are sure of this, you will note that the bushing often needs to be opened up a little. Simply slip a flat head screwdriver in the slot, and gently tap on the butt of the screwdriver until the bushing spreads enough to get it on the shaft.
Metric SK Bushing
Above is a Metric SK sized bushing. If you look closely you might see the SK followed by the size. You’ll also note six holes: three are larger and unthreaded and three are threaded.
SPLIT Tapered Bushing With Screwdriver
Note the split in the photo above. This is a SPLIT Tapered bushing. We can drive a screwdriver into the slot to help spread the bushing a little to get it started over the shaft.
Pulley In Jacking Position
Above we see the bolts in the threaded holes. Note the end of the bolts are pushing on the face of the pulley and this will jack, or help remove, the bushing from the pulley. Since the bushing and the center hole of the pulley are tapered, they are always easy to pull, even with gloves on!
Most Common Bushed Pulley Mount
Shown above is the most common method of mounting a bushed pulley. The FACE of the bushing (top most in this picture) is installed nearest to the end of the shaft so it is easy to use the jacking bolts and easily remove the pulley. Simply remove these bolts and then install the jacking bolts. In the photo you can see that the bushing is NOT brought in tight against the pulley. This is normal, and there is no reason to tighten the bolts past snug. There have been several people new to tapered bushings that have broken off the bolts trying to pull the bushing flush to the pulley! The two tapers work to secure the pulley onto the shaft as if it were welded on! Don’t get carried away, but do go around in a circle and tighten the bolts a little as you go round and round to allow the pulley and bush to seat evenly, which will allow the pulley to fully align on the shaft.
Less Common Mount Method
Above is an optional (seldom used) method to mount the newer Utterpower Pulleys. The bolts are passed through the unthreaded holes in the pulley and into the threaded holes in the bushing. In this case, the bolt heads would be outward, and the threaded holes in the pulley would be used as the jacking holes. This option is not possible with many pulleys, and one must inspect the threaded hole and be sure they are threaded all the way through before mounting.
One other item worth mentioning: Do not assume that the bolts and threaded holes are the same! In this case, and other cases, the holes in the the pulley are 8.8 M8 Metric, and the bolts in the bushing are typically 5/16 18 thread for the SK bushing. Make sure you check these things out and have the proper bolts before you attempt to install the pulley.
This post is intended to give you some very basic advice. There are other excellent posts and pages to be read. Here is one example. I recommend a Google search of “QD bushings” to assist your learning.
Thankyou very much for posting this article on bushed pulleys. I had never seen one before, and had no idea how to remove it.
Pete
Why do pulleys (sheaves) come in such unorthodox sizes? I.E., 13.6, 8.2, 6.4 etc.
Two pulleys of significance have everthing to do with the rim speed of cast iron, and the frequency and number of poles in a generator.. 60hz and 50hz are often the goal.