ORIGINAL: geh3
Just remember that all turbines WILL require a set of bearings eventiually and this is based on running time SO if you waste running time on the bench you will have less time in the air until you will need to send it back for bearing replacement!!!
I posted elsewhere on another thread about a Wren MW44 with 870 minutes running (another Wren had twice this time) on it and no bearing change, so set up correctly these GWR cageless bearings may run for a very long time in the air at upto 195,000 rpm. The principle difference with JJ turbines is in the build of the oil byepass flow to the rear bearings, also the engineering tollerances and lack of customer filtering that have led to earlier bearing failures. The is not to say that late JJs have not improved, rather that there are many early examples that are sub standard. The early IC Chinese engines of SC and ASP also often arrived full of swarf inside and self destructed the piston+liners on the first run. Its a learning curve for the factory and the buyers.
Paul