RE: JJ1400 14lb Turbine Stripdown/Rebuild
Replacing the front bearing is an easy enough job as it is removed during disassembly. Some builders fit a lower spec bearing at the front being cheaper as it is easy to change more often,
The rear bearing replacement requires that you remove the turbine wheel from the shaft.
Again mark the shaft to the turbine wheel position, this will save you having to balance the turbine on rebuild, I will be detailing later how to balance it anyway if needed.
The nut on the end of the shaft will be much tighter than the one on the compressor and this is supposed to be like that. This is so the compressor nut will always loosen first as you may not want or need to remove the turbine wheel ever time.
I found the best way to loosen the nut was to put the shaft in the chuck of my lathe, left hand thread again and a 8mm ring spanner needed. Note the orientation of the spacer behind the turbine wheel as it tapered, the larger diameter goes against the wheel.
After cleaning and inspecting the shaft/wheel a new ceramic D688/602976 GRW bearing can be fitted. The bearings have an arrow stamped on the outer case, (see pic) this is for fitting the correct way around, the arrow points out towards each wheel. The reason for this is the bearing inner race is tapered.
Make sure you line up your mark on your shaft with the one on the turbine wheel and reassemble with the new bearing arrow pointing at wheel and the spacer with the large diam against the turbine wheel.
Put a tiny smear of oil on the nut face (helps getting correct torque) and tighten the 8mm nut (Left hand thread) to 100-105 lb-in, (11.3nm-11.9nm). I used my own experience on how tight to make it, as I did not have a torque figure at the time.
The turbine wheel nut must be tighter than the compressor wheel as it has to stay tight when removing the compressor nut first when dissasembling the turbine.