Fretting ??

Discussion in 'Transmission' started by HarryB737, Sep 21, 2011.

  1. HarryB737

    HarryB737 Junior Member

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    Here is an article that might shed some more light on the Fretting issues. This came from an engineer from Dupont: Talking about pump shaft fretting
    What causes this fretting problem?
    Surprisingly, it has nothing to do with dirt in the air or abrasives in the fluid. The problem will occur even if you are pumping a filtered, clean lubricant in a sterile atmosphere.

    To understand fretting you must first understand the term "corrosion resistant". Some materials resistant corrosion others do not. What's the difference? We say that iron rusts, but aluminum oxidizes. A look at any dictionary will verify that these terms mean the same thing. So why do we use different terms to describe the same problem?

    The answer lies in the way a metal rusts or oxidizes. If the oxide layer is protective we say that the material is corrosion resistant. Take aluminum as an example:

    Aluminum metal protects its self by forming a layer of aluminum oxide on the surface when it is exposed to oxygen. It's very visible and looks almost white in color.
    A more common name for aluminum oxide is ceramic; a dense, hard, corrosion resistant material.
    After this dense, ceramic layer is formed on the surface of the aluminum, the oxidation or rusting rate is slowed down to less than 0.002 inches (0,05 mm) per year, and this is the definition of corrosion resistant.

    If this protective oxide layer is rubbed or polished off by the packing, lip seal or Teflon wedge the oxide will immediately reform to protect the base material. It is this constant oxide removal and reforming that causing the shaft grooving that is so visible. We get the same reaction when we polish silver. The "tarnish" replaces its self to protect the silver.

    Shaft vibration and end play causes a constant axial movement of the shaft through the mechanical seal dynamic rubber or Teflon® part. Bearing grease seals and stuffing box packing are stationary, so the rotating shaft is constantly being polished by these materials when the pump is running

    There is a second problem associated with fretting. The ceramic oxide that is removed imbeds its self into the rubber part causing a wear or grinding action on the base metal.

    Stainless steel protects its self by forming a protective oxide called chrome oxide, one of the hardest ceramics. When this oxide forms we say that the active stainless steel is now "passivated". It is this chrome oxide imbedded into the packing, Teflon®, or rubber lip that does so much damage to the shaft sleeve.

    So now we have two causes of fretting:

    The removal of the passivated layer by the rubbing action of the rubber or Teflon®.
    The hard ceramic that we removed sticking into the rubber or Teflon causing a grinding action.
    Now that we know the causes of fretting, how do we prevent it?

    Replace bearing, lip or grease seals with labyrinth seals, or the newer positive face seals.
    Stop putting cut packing into pumps. You don't need that kind of leakage any more.
    Do not use mechanical seals that are designed with a dynamic elastomer positioned on the pump shaft or sleeve. Most original equipment seals are designed this way. Stationary cartridge seals, most balanced o-ring seals and all properly installed bellows seals eliminate the shaft dynamic elastomer and the fretting associated with it.

    What I am thinking is... perhaps we're going in the wrong direction when it comes trying to solve the problem of Compensator Fretting. Maybe the Compensator itself & its components need to be constructed out of a different material... such as a hardened stainless steel to prevent the corrosion process.... Just a thought :D
     
    Last edited by a moderator: Sep 21, 2011
  2. Hoople

    Hoople Account Removed

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    Great thought but aren't we looking for an easy affordable way to "fix" what we were dealt by the Moco using simple common hand tools?

    I barely have access to a quality drill press much less a metallurgy and hardening/tempering facility.:)
     
  3. HarryB737

    HarryB737 Junior Member

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    That's just it, what has been tried thus far does not appear to be working. Some things might not be able to be resolved easily or cheaply. Perhaps an aftermarket Machine company can design & manufacture a product that does not corrode so readily in an Oil Rich environment as the Compensator is in.
     
  4. glider

    glider Veteran Member

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    I think the MOCO has to go back to the drawing board on this one and redesign the compensator using a different approach.
     
  5. Jack Klarich

    Jack Klarich Expert Member

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    Like the grease fitting on my 60 FL never had problems in the old days til the MOCO decided to reinvent the wheel, Dont get me wrong they have made big improvements since the Panhead days but alot of what I see now is CHEAP:s
     
  6. R_W_B

    R_W_B Senior Member

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    I've seen pics of the old SE Comp and the new type 'A' comp and they are designed different. But still no grooves in them. I agree Moco really disappointed me on the Comp situation of which could be in my face at anytime since I'm coming up on 16,000 miles.

    I know that (as Harry stated) stainless steel shaft pump motors last longer. But the torque stress put on a Comp it would be hard to get a Stainless product that tough.
     
  7. gs34

    gs34 Junior Member

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    Wellll guys, I'm sticking with my original comments on this issue. fretting and metal erosion on stock compensator - Page 4 - Harley Davidson Community
    Currently My 07 is sitting right at 72,000 miles, which makes it 61,000 on the SEcompensator.
    Still say it's pretty much the same as when I installed it.
    Not hearing anything unusual....not seeing anything abnormal on the mag plug when I change oil.
    And, I'll add to that....I haven't touched my clutch adjustment since I put the compensator on.
    Y'all must really like tearing stuff apart and looking at it.
    Myself, I'm riding, and if it ain't broke...I'm not looking for a reason to go poking around trying to dream up problems to fix.
    Me'thinks many of you are "jousting at windmills"!
    But then.....that's just my opinion.
     
  8. HarryB737

    HarryB737 Junior Member

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    Good for you GS34, I personally hope you get 100K more miles with smiles on your set up. I appreciate your comments !! :D
     
  9. Hoople

    Hoople Account Removed

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    Actually I do! :) And it usually winds up costing me money in parts, tools and time but that's a cheap price to pay for the knowledge.

    I was very surprised of what I found this last go around . I was expecting to find an oily slurry of orange fret rust and oil but I did not. I found completely dry, yes complete dry (powder) fret rust. It was packed between the shaft arbor and the 3 spoke gear. It was not oily or dripping out of the arbor.

    The powder causes the 3 spoke gear to stick to the arbor. The gear sticking to the arbor won't create unusual noise. It will not change the color of the oil to orange. The fret rust will not go to the drain magnet because it is dry packed in place. All it does is cause the spoke hub to stick to the arbor. The spokes no longer climb up the ramps at will. But when they do, it will be more of a dry chatter than a smooth climb. Therefore the compensator no longer absorbs crank shaft inpulses the way it was designed.

    If you were to mig weld the compensator together as one piece, you would not start hearing banging or metalic noises. I would also get 100K out of it but it would not do much to absorb crank impulses. Broken or weak springs is a totally different thing. We are not dealing with that. We are dealing with a compensator that sticks and jumps into place rather than having a smooth transition or rocking action.

    Not saying any of this is right or wrong. Just reporting what I found on my bike along with my theory on it. Nothing more.
     
  10. HarryB737

    HarryB737 Junior Member

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    So Hoople, do you recommend on a new SE compensator install,.. to run for about a season, take it apart, clean things out & then reinstall & enjoy?