I am only speaking of engine, trans ,and primary. Our bikes now have 1 oil for all 3 so there is clutch dirt that gets in the oil from normal wear. All I was saying that it has been my experience with almost (can't think of one that didn't) every bike I even rode or was owned by a friend had a separate oil for the primary so clutch dirt and friction modifiers in the engine oil didn't matter in that respect. The bulk of my experience is Triumph,BSA,Norton,and Harley. I do remember a shovel that had a common oil for the primary and engine but the ones I saw had return problems and most guys blocked them off so there were separate oils.
