I put a matched set of 0s in my lathe about 5 or 6 years ago and had an experienced machine guy tell me to tighten the preload until I could raise the bearing Temps about 40 degrees with a 20 minute run. I did that and everything ran great, and still appears to be, but I just rechecked the heat after several years and I could only get them up to 77 degrees instead of the 115 degrees when I did the install. I'm tempted to just flush the old oil and up the preload again until I get the heat I'm looking for but don't really want to spend the bucks on a new set if I screw them up. Any of you ran into this situation before?