I pulled that fork tube apart "again". The tube is straight using my cast table saw top, roll test. The aluminum tapered bushing (part #8, taper spindle in the diagram above) that gets sandwiched between the damper rod and the bottom of the lower seems to be where the "bottoming stickiness" comes from. Inspecting a few of the taper spindles shows some wear on one side from the inside of the fork tube rubbing on it. On my third try tightening the bottom bolt with the fork tube fully pushed in to hold and center the taper spindle the tube will now bottom in any position without binding, so I am going on the theory that centering the spindle with the tube collapsed during final bolt tightening is "good practice". With a proper damping rod holding tool this isn't too hard to achieve. Unless I miss my guess the function of this piece is the final cushion before bottoming out the fork as the oil is forced through a rapidly closing taper it slows the last few mm of travel reducing that awful slam stop you you would otherwise get.
Before and after pics of the damper rod drilling.
You can see the wear marks on the taper spindle from the "sticky" fork tube.
This section has been amended above.
On the tube stick the bottom of the tubes is machined and some of the unmachined tube ends is still there It might be just how things line up and "jam" a part of the end machining inside the lower?? That's my current theory anyways. I'll double check for tube straightness because you got me wondering. I am "rather sure" these tubes are straight though.
Before and after pics of the damper rod drilling.
You can see the wear marks on the taper spindle from the "sticky" fork tube.
This section has been amended above.
On the tube stick the bottom of the tubes is machined and some of the unmachined tube ends is still there It might be just how things line up and "jam" a part of the end machining inside the lower?? That's my current theory anyways. I'll double check for tube straightness because you got me wondering. I am "rather sure" these tubes are straight though.