I saw a trick somewhere in this thread where someone removed the O-ring and took a steel punch and made 3 dimples at even points (120 degrees) around the outside of the rear outer bearing race which creates enough of a rise in the race material to make the outer race grab the tunnel. I'll look for the post and put it up. I have never tried this but it makes sense. The dimples are in placeof theO-ring.I wouldn't think your preloadchanged either but sometimes the O-ring does hangon thebearing which can cause the dragging issue. I just took apart a motor recently that had a real bad issue with the bearing hanging at the O-ring. I cleaned and polished the tunnel sleeve insert and made sure the insert was moving freely. I even went as far as torun some very fine grit wet sandpaper (~1000 grit) with oil alongthe O-ring and tunnel interior to make sure itwas smooth.I would have changed the O-ring but Ihave no clue whatsize it is. You really want free movement of the sleeve and for the insert to protrude about1 mm orso when you press it in. If you press it in and it stays there, you have an issue.The O-ring keeps the outer race from spinning with the inner race in the tunnel. Ihave heard a lot of people say they take out the O-ring and that they have not had issues but if you look at what happens when the bearing does start to spin from not having an O-ring,there can be some resultant damage to the tunnel.
General rule I have heard is that you are better to have preload too low than too high.
I would try lubing the thing before ripping things apart.
Martin... Question for you ... if you spin the turbine by hand, how long does it continue to spin for?
How can Itell if Ihave a bad bearing or if I have excessive preload??
Irecall when I assemble the engine that I left a little movement of the shaft (with preload) but I wasnt sure how much was too much or too little
Also - Ithink the rear O-ring was installed - what effect does this have if it is removed?
A bad bearing is not going to get better once it starts to bind and/or whine but excessive preload or a gummed up oringwill definely cause bearings to become draggyfor sure.
maybe i have a solution for draggy bearings.
i had it with my homebuild 54 turboprop, and what i did was spreading only kerosine in to the feedline from oil .
Then spin it a few times with air , and then start it up.
the bearings ran much nicer after that.
what i noticed was , after a while the front bearing will be stuck a bitt in the o ring, and if you spread a bitt of feul into the feddline , the bearing came loose again , and the running was much better.
i dont do it every time , 2 or 3 times in a year.