Timing Belt Idler Pulley question

The center of the pulley is fastened to the engine block and stands still. The outside of the pulley spins when the belt moves. The difference is resolved by a ball bearing in the middle.

I guess it boils down to this-- The pulleys have a bearing that is sealed. Bearings that have grease lubrication should turn without any roughness, and have a very light resistance due to the grease. To me turning freely for a bearing meets the conditions above. Now if you think turning freely means that you can easily spin the bearing at a high speed, and it continues to spin for many revolutons without more applied energy, then we have two different ideas of turning freely as applied to lubricated bearings.

Now if you want a bearing that turns more freely than most, I'd like to mention the bearings on a moderately large generator powered by a multi thousand HP motor. First, the bearings are pressurized to a fairly high pressure (~5,000PSI), and are oil lubricated. Next you push with both hands against the shaft and coupling between the motor and generator. After several minutes, the shaft will turn slowly. After you remove your hands the shaft will contine to turn for several minutes, but for less time than you pushed on it. (The generator was designed to be spun up to speed by the motor, then the motor was turned off priot to applying a large load to the generator.) The intended use was to test electrical devices under catastrophic failure conditions. The generator was capable of dumping a meagawatt per phase or so into a load. (Stored energy in the rotating mass of the generator) The generator was mounted on what was roughly a cube of concrete and steel structure about

Chuck, It's not what "I think", is the point here. I know when the belt tentioner and idler for a miata are ok to use and when to throw them away. It was a question that was asked to the people on this site. Should it "Spin". It looks to me that we have long over answered that question ! Thank you for the long disertation on the subject you covered. I don't know how I could have gone on in life without knowing all of that. Thanks again :-)

Bruce Bing '03 LS

Ah, the wonders of Newtonian viscosity.

Eat more spinach.

Leon :)

Of course - the new idler pulley showed up - took everything apart to install it - and it works much better than the old one. But to make my life ever more challenging - the company did not ship the correct tensioner pulley - despite what the invoice said they sent me another idler pulley for another type vehicle. Oh yeah - the saga continues.