by bryancobb » Wed Feb 05, 2014 4:50 am
Back to your original post and the problems after maintenance.
** Did the mechanics have the Maintenance Manual IN THEIR HANDS as they replaced your Outer Pylon Bearing Shafts?
If they were strictly told to ONLY do necessary work related to the OPBS's, they would have:
1) Removed AN-3 Damper bolt from T.E. from each blade
2) Remove Outer blade pivot bolt and remove each of the three outer blades
3) Remove two screws and remove grease retainer disc from each blade accessing blade retention nut
4) Disconnect each Pitch Link from each Inner Blade Pitch Horn (WARNING: use the correct thickness of conical washers when re-installing and MAKE ABSOLUTELY CERTAIN the two ears of each Pitch Horn are NOT squeezed together as the AN-4 bolt is torqued...THEY WILL BREAK OFF)
4) Remove Blade Retention Nut and carefully remove each inner blade from pylon by pulling outward
From that point the OPBS's can be removed and replaced by drilling out the single Keeper Rivet and unscrewing the shaft.
Here's some of my thoughts about what could have happened to cause your problem.
* They "probably" didn't touch or disturb the 4 feather bearings in each blade. These bearings are hard to get out and they come off when the inner blade is removed and they all 4 stay up inside the blade.
* There's a very thin single feather bearing, and a rubber Rain Seal at the ROOT of each inner blade. If The rubber seal is old, it can crumble into pieces. The inner blade relies on the thin bearing and the rubber rain seal to center the root of the blade on the pylon and keep it centered as cyclic and collective moves the pitch horn. The rubber rain seal may not be centering the blade on the pylon and could be your problem on one or more blade.
* If any ears are cracked or broken off any pitch horn, That could be the your problem.
* Inner blades MAY have been re-installed in another position from where removed.
* An inner or outer blade could have been unknowingly damaged during removal or installation.
* Seems like I remember reading SOMETHING about Outer Pylon Bearing Shafts that were manufactured with CUT THREADS and ROLLED THREADS. The ones with ROLLED THREADS are the only airworthy ones and that same letter spoke about how to install them while insuring their base flange contacts the tip-end of the Pylon Tube at all 360 degrees around, as it is screwed in. That is sooooo critical and IF yours didn't, the OPBS MAY be cocked to one side and not parallel to the Pylon Tube centerline. This would make feathering be "notchy" and could cause your problem. (Where did you get your OPBS's that you had them install?) I had a BRAND NEW uninstalled set with rolled threads that I bought from Brantly in 2003. They are SOMEWHERE right now with the new owners of N2175U, I suppose?
* An OPBS retaining nut COULD HAVE been left loose.
THAT'S ALL I CAN THINK OF
YHO-3BR Pilots International