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Thread: loosening up tight bearings...

  1. #1
    Join Date
    Feb 2009
    Location
    Indianapolis
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    82

    Default loosening up tight bearings...

    I'm building a small engine emulator stand, just a shaft with a flywheel toothed wheel and a crankshaft position sensor. I have the shaft supported on both ends with pillow block bearings. I am driving it via a small series wound AC/DC motor with a variac, and a large O-ring for a drive belt.

    The bearings are brand new, so they have a lot of preload on them. The motor doesn't have enough balls to turn the shaft because of the stiffness of the new bearings.

    Anyone have any ideas how to loosen them up, save running them for countless hours? The only idea I have is to take off the shields, flush out the grease, fill them with toothpaste or other very fine abrasive, and run them for awhile to accelerate the run-in process.

    The shaft has no load, and will only be used for a few minutes at a time, so it is not like I need to worry about bearing life....

  2. #2
    Join Date
    Jan 2005
    Location
    Buffalo NY
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    1,944

    Default

    What is the number of the bearings?
    Are they designed to have internal preload?
    Usually regular ball bearings do not have preload.
    You can buy them that way, more expensive.
    Metal shields are a pain to get off without damage.
    Rubber sided are easy on/off with a dental pick.
    If it is just hard grease, soak them in mineral spirits.

    --Doozer

  3. #3
    Join Date
    Feb 2009
    Location
    Indianapolis
    Posts
    82

    Default

    Thanks for the reply. They are SA204-12 bearings. I took the bearings out, they looked to be just metal shielded, but I easily popped off the metal shields, and they have a tiny seal on them. Most of the "preload" was due to the seals.

    They had fairly heavy grease in them, which I cleaned out with mineral spirits. I oiled them, and tried it out. Although the shaft spins free now with the seals off and oiled, my motor still doesn't have the balls to turn the shaft. I think the o-ring drive belt just has too much friction.....

  4. #4
    Join Date
    Aug 2009
    Location
    Canada, Bc
    Posts
    7,338

    Default

    You could easily use a 555 to simulate the crankshaft position sensore if its not a 'missing tooth' setup.

    Alternately a avr could easily be programed to fully simulate the crankshaft (with or without missing tooth index) and other digital sensores for running an ECU. (Some avrs even have a built in ADC, so you can hook up a pot for 'virtual' speed control)

  5. #5
    Join Date
    Jan 2003
    Location
    Chilliwack, B.C.
    Posts
    9,188

    Default

    If I have it right, you want to spin the shaft fairly slowly as a demo, so gearing down (or belting down), you'd have to use a pretty high ratio to keep the motor happy and keep the crank at a suitable speed. You might have to go two stages with pulleys, or use a flat belt and run it right on the motor shaft.

    You want speed control, but the type of motor you want to use doesn't like to be run slowly and loaded down that much- If you can do without speed control, you might consider going with an induction motor, a slower speed one, which would be 1725 rpm, and getting all the speed reduction through the pulleys. The first belt, or O-ring off the motor can be lesser diameter, and that will ease the motors job.

  6. #6

    Default

    Maybe you could adapt a variable-speed drill motor to run the emulator.

    Post a picture of it, so we can see what you're dealing with.

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