Miniflyer

Hy,

126k RPMdefinetly should not be a problem for a standard KJ66 setup, given that it is a good turbine wheel, good bearings and a standard internal setup with a perfect balance.
If it was not a bearing failure i'd think you pobably had it off-balance....a du-bro will NOTdo! You need to have it dynamically balanced...the equipment you need for that is pretty complex, your best bet is to send it to somebody to balance it for you. Rescue Turbine Service can do that for you, so can Wren.....
They will also mark the position in which it was balanced, because if it is reassembled just a few degrees different from the last time, balance will be off again!
Just a tip: if you start it up to idle RPM, hold jour fingernail to the housing. If you feel more than just the tiniest of vibration, shut her down and have her balanced! That is the first thing i do when i start up a homebuilt, and i recheck every RPMincrease for vibrations.....

By the way, the sliding fit between the shaft tunnel and the NVG is to allow for temperature expansion. Steel and Aluminum have different temp coefficients, and therefore will grow and shrink differently. The sliding seat will allow it to adjust without putting unneccesary loads on any parts.
You can also use a steel shaft housing and bolt it to the NVG, but then you will need a sliding seat to the housing. Both variants work, both have their advantages and disadvantages.....

best regards
Hank