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« on: February 12, 2007, 12:38:57 AM »
 I was reading the topic about disassembling an ST head and wanted to make a few comments about bearings. In my 25+ years of wastewater work, I've seen lots of bearings replaced. We had professionals of all types teaching us at seminars about how to work with them. SO, I am familiar with how to handle them.Â
 Now just a few things said in a general look for way.Â
1) Whichever part of your piece of equipment truns should have the bearing race a heavy press fit. Heat then slip on.
2) Whichever part of your equipment sits still while it's running should have the bearing race be a slip fit.Â
 The reason is: Bearings are designed to slowly rotate when in use. Think of it this way. The weight of things sit on a small spot at the bottom of the bearing, if the races never turn all the weight will cause enormous wear on that spot and nowhere else. The material of the races is designed to 'squish' just a litle bit under pressure. So, in the case of an ST head, if the end bell side race is a slip fit, the 'squish' will cause that race to VERY SLOWLY rotate, thereby exposing a new surface at the bottom as it runs. This will extend the life of the bearing tremendously.Â
 The race sitting on the rotating shaft needs to be a very tight fit so that it won't rotate. Here the situation is that when the rotor starts to spin, and when it changes the rate of spin, the race tends to lag behind. This tends to scrape or gall the surface of the shaft itself.Â
 SO, The rotating piece gets a tight fit, the stationary piece gets a slip fit (NOT a loose fit), and the bearing and equipment lasts much longer.Â
 3) Bearings are made of pretty hard metal. Never strike them with a hard metal object. This will cause them to crack. SOFT metal like brass can be used with much better luck. You may not see the crack that you create, but, it will show up later as a failed bearing. NOW, this isn't to say that some highly skilled, highly motivated people can't use a get-a-round and have it be succesful, just not the run of the mill people like most of us. My Father used to remove old bearings from 6" & 8" shafts by using an acetylene torch and ice water. Heat a spot on the outer race to red hot with a torch, chill with ice (or cold) water, repeat the operation at 180 degrees. Then strike each spot with a heavy hammer, The race will shatter at each spot and the race will fall off. Use a pair of pliers (or other item) to remove the balls and cage, then repeate the heating-chilling-striking procedure on the inner race.  This will get off the old bearing without harming the shaft at all. Some people (including my Father occasionally) use a cutting torch to cut the races in half, BUT, you probably will cut into the shaft material itself while doing it. This means hundreds of dollars to machine down the shaft and fit a new specially machined sleeve if you are VERY carefull and lucky, OR, several thousands of dollars for a new shaft and its' installation if you're not VERY careful and lucky. City governments frown on this kind of expensive wastage.Â
Since it's our own personal possesion that we're working on here, it would be nice to use the best technique you can manage. Any other comments are welcome here.
If your bearings are loose where they should be tight, it can be fixed. If it's tight where it should be loose that's even easier to fix.