Fork oil observation and question

Discussion in 'Workshop' started by faffi, Dec 2, 2017.

  1. faffi

    faffi A.S.A.N.

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    In my experience, fork oil gets contaminated quite quickly. Especially in old forks. However, when my son's CB400SF developed a leaking fork seal, the kid wanted thicker fork oil than I had available at the moment. And since we had a trip planned for the following day, I filled the fork with engine oil 10W40.

    Other than him getting much firmer damping as required, what surprised me was that when I emptied the fork legs after I binned his bike, the engine oil was utterly clean.

    So the question then must be; does the engine oil provide better protection, or does it just not mix with the contamination?
     
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  3. lindsaymac

    lindsaymac Can't reMember
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    Maybe it hadn't been in there long enough to collect any?
     
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  4. faffi

    faffi A.S.A.N.

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    Could be, but the 8000 km old (from new) oil in my MT07 was pretty dirty. I think the CB only had 3000 km on it when I binned it, but I would have suspected at least some discoloration. Instead, it looked like it had just been poured from the bottle.
     
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  5. RUSS M8

    RUSS M8 Riding slowly on

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    very interesting.
    when I was taking my road racing seriously the fork oil was changed every 6 months.
    so we are talking every 4 days at the track or so, maybe every 200 - 300 km?
    it always came out quite dirty.

    Maybe the engine oil came out clean as the fork oil is designed to keep the contaminants in suspense rather than letting them loose?
     
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  6. faffi

    faffi A.S.A.N.

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    I was thinking the same thing, that the engine oil doesn't keep the particles floating, but letting them fall to the bottom. Would be interesting if it could be confirmed, or if the reason is something else.
     
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