Burr from sprag bearing on upper gear hub.

[Hardcarve1]

Just doing my service on my FAI tempest auto-rotation sprag bearing to oil it up and each time I do this it's always hard to separate the main gear from the upper gear. Even when you rotate the upper gear to release the sprag bearing it always is hard to remove. What I keep finding is a small burr is formed top and bottom of where the sprag bearing makes contact with the upper hub. I take some wet and dry sandpaper and give it a light sand and it solves the problem. I also have some ridge marks on the hub from the sprag bearing but these are very light and almost sand out.
The heli has about 80 flights in it and I use 30w engine oil in the sprag bearing which always has oil remaining when I service it.
Does anyone else have the problem with the burr and should the hub have no trace of sprag bearing grooves no matter how small.
Should I try another oil.
Alex

[Shannon Davis]

Mine always has a new burr- I have used several different lubes-- the burr is alway there. I don't know how many flight are on the machine-- several hundred-- and it has never been any issue-- except for conviencing it to come apart. Force is not the answer-- just wiggle and jiggle and you will find the sweet spot and it falls apart. :D

[DavidH]

It is fairly common for a small groove to be worn into the tube. Yes it does may it a problem to take apart. I just tap the bottom of the tube with a rubber mallet and the crown gear and tube will come right out. I then also take some 400 or 600 grit paper and polish the tube back to specs. From my experience, usually after the initial wear in on the tube, it does not happen again after the first time. I use Tri Flow oil or Automatic Transmission fluild for lubricate in the hub.

David