The double bearing mod is fraught with danger....In my opinion, too much metal needs to be removed from the hub to allow the second bearing to fit.....The main damage however, is usually caused when drifting in the two bearings...One tap too many, or too hard may crack the shoulder from hub, and then it is only a matter of time before the hub finally collapses.
I searched long and hard, for what I considered a suitable bearing for this modification, and finally came across a
NSK double row "Angular Contact Bearing", one that I considered to be perfect for this application.
In the pic below, the original bearing is on the left and the
NSK bearing on the right.
The
NSK bearing has an overall width of 22.2mm, requiring 7.2mm to be machined from the hub and spacer bush. As opposed to to the 15mm required, if you are going to fit two bearings.
Provided the hub is set up accurately in the lathe, boring to the required debth is relatively straight forward. Just take it slow and steady, with regular checks of the debth of cut using vernier callipers.
It is also highly recommended that the boring bar tool tip is slightly radiused so that you do not end up with a sharp edge transition at the end of the cut....
As can be seen in the last pic, there is still plenty of "meat" left in the hub, to support the bearing.
I have done over 20,000Ks on this mod without any problems....(still on the same set of PU cush rubbers).
NOTE: This post has been edited to reflect the fact that I used a NSK bearing...not SKF, as originally posted.