Just another thought on this... what about needle bearings? You get many more of them, they are longer, but the only problem, are they sealed like the roller versions?
I am not an advocate for either bushings or bearings. I just want to point out that these comparisions to spindle bearings may not be quite accurate. Think about how a bearing works on a spindle, the inner or outer race is typically moving one dirrection around the other thousands of times. In the case of roller perches the inner and outer races will never move more than a few degrees its whole life, and this small movement is what drastically shortens the life of the bearing. It has been my experience that if there is less than 180 degrees of movement a bushing will last much longer. One final thought, think about the cam, rod, and main "bearings" inside your motor. They are really bushings and they can last for years at several thousand RPM's. Again I am not advocating the use of one over the other, because either is a drastic imporvement over stock.
The bushings in an engine require a pressurized oil film to function. You can't run a bushing at high speed where the two parts actually touch. It won't work. The parts rapidly gall and get hot and then seize.
Can you give me a few examples of applications that have less than 180 degrees of rotation and the bearings wear out whereas bushings don't wear out? You say it's been your experience, describe your experiences, please. The applications I've seen - like beefy hinges for really heavy doors - use bearings and they work great forever. Do you think someone would put bushings on the door of a safe, for instance? I would expect that it would be impossible to open.
The advantage in a roller bearing is you have rolling contact. You are not sliding two surfaces past each other. Oil or grease in a bearing serves to keep the bearing cool. The internal parts do not ride on a film of grease. In this application the bearing won't get hot anyway. I can't think of any reason why a smaller amount of rotation would cause any problem at all. I have an open mind about it, but I sure can't think of a reasonable explanation.
Just another thought on this... what about needle bearings? You get many more of them, they are longer, but the only problem, are they sealed like the roller versions?
If you aren't sure, consult the experts. If you google McMaster-Carr, then do a search on the word "bearing", you'll get an explanation of which type of bearing is best suited for an application.
Of course, another way is to look up the load rating and size of bearing you need and find one that fits.
If I were to build an assembly with bearings, I would want to make sure the bearings accomodate misalignment. Maybe just a lack of confidence in my ability to make something very precise, but binding would be my main concern. Binding could shorten the life of the assembly quite a bit.
It appears to me that the load capacity of the needle bearings is higher than the roller bearings.... binding could be an issue, but you wouldnt need to crush the outer sleeve to make room for the shock bolts, so it shouldnt be a problem. You can always get the single sealed bearings and put a grease fitting in the middle of the sleeve also.
The bushings in an engine require a pressurized oil film to function. You can't run a bushing at high speed where the two parts actually touch. It won't work. The parts rapidly gall and get hot and then seize.
Can you give me a few examples of applications that have less than 180 degrees of rotation and the bearings wear out whereas bushings don't wear out? You say it's been your experience, describe your experiences, please. The applications I've seen - like beefy hinges for really heavy doors - use bearings and they work great forever. Do you think someone would put bushings on the door of a safe, for instance? I would expect that it would be impossible to open.
The advantage in a roller bearing is you have rolling contact. You are not sliding two surfaces past each other. Oil or grease in a bearing serves to keep the bearing cool. The internal parts do not ride on a film of grease. In this application the bearing won't get hot anyway. I can't think of any reason why a smaller amount of rotation would cause any problem at all. I have an open mind about it, but I sure can't think of a reasonable explanation.