Thanks!
I removed the gearbox and power turbine from the bike today for the upcoming test where I will run the gas producer with only a temp probe and a short section of pipe without a jet nozzle.
While I had the freepower section removed I wanted to see how the internals of the gearbox was holding together, so I removed the C20 turbine wheel and found this:
Hmm, must be oil from the bearing lubrication that has overheated. That might be the cause for the slight rubbing I could feel when turning the input shaft, it called for further investigation.
It wasn´t hard to spot the problem, the composite cage for the front hybrid bearing had melted as you can clearly see in the pic below. Good thing that I decided to check since another run with this bearing could have ended in disaster.
It wasn´t completely unexpected, I had hoped that the bleed air flow through the bearing would keep it cool enough for the cage to survive but that was clearly not the case. Before spending even more money on a full complement ceramic bearing I will try a standard steel C3 bearing and see how well it survives, if I´ll make sure not to overspeed the gearbox perhaps it can endure the stress.
Cheers!
/Anders