> river 2strokes Wrote:
> My only concern when putting the bearings on the crank first is then at
> that point you can’t seat the crank unless you get lucky with both
> bearings magically seating into their journals. It won’t magically seat
> itself after a heat cycle either, because thermal expansion will
> basically lock it in place.
> And even if you do install the bearings first that doesn’t necessarily
> mean the crank is aligned to the center of the cylinder. Yes the big and
> small end bearing tolerance will allow the piston to move freely, but
> short of that there is no real way to dead center the rod with the
> piston and cylinder for perfect alignment.
> That’s where the emery cloth and lathe come in.
> Imagine sliding a main bearing on with little friction at room
> temperature. More free play means faster spin up when running. Do that
> to both bearings and install. There is enough free play at room
> temperature that you can slide the crank back and forth between the
> bearings in the assembled crank case.
> I know this sounds like a loose bucket of boots waiting to happen BUT
> The motor spins at idle, the free play allows the crank to perfectly
> align itself in the top end due to inertia, and when the whole system
> gets to temp thermal expansion will lock it in place. Now you can
> imagine what happens when a normal bearing shaft are mated the inner
> race will actually expand and press the balls or needles into the outer
> race and cause more friction - with a little bit loose tolerance the
> expansion the friction is minimal on both races. Picking up what I’m
> putting down?
> The difference in revs is 100% noticeable