1 Consult your engineer you say it is unusual, DO NOT FLY.
2 has there been any metal in the engine filter on the last two oil changes.
3 if you have an extra spin on filter did you cut it open and examine for any metal
4 recently a head and mast assembly fell off a KH4 causing it to descend quickly (surprise) from its luckily very low altitude.
5 no one but no one has talked about what must have been chronic filter contamination that time for at least the last two oil changes. in that case the tip is that the mast bearing let go after what must have been large amounts of evidence in the filter
6 in this case it could be that your spigot bearing in the xmon at the bottom of the mast has collapsed
7 it could also be that your mast has broken just above the spigot bearing in the xmon
I have seen both situations and in either it could be that metal has not yet accumulated in your filter,
8 check that your four gimbal bearings are not worn and particularly that the head is not being allowed to float from side to side i.e. longitudinally. also that the gimbal is not broken
8 (a) check that the trunnion is not broken off one end wear it goes into the gimbal
9 check that your sprag mounts (there are two on the KH4) at the bottom of the engine is secure on to the mainframe, and of course that the sprag rubbers are not broken
10 never but never fly with a deteriorating lateral. it could be a sign of a cracking mast. or other terrible things
11 make sure that the engine basket does not have a broken tube.
12 make sure that the power cylinders and control rods are all attached securely
13 it is imperative that you check that the stab bar, damper frame and damper clamps are not cracked or broken or that either damper is not broken on the shaft where the damper arm connects.
never but never fly with a US component anywhere near there. one broken damper makes it squashy, a completely disconnected damper assy means extremely scary and super sensitive over controlling of feedbacks. usually a crash will ensue.
14 in all of the above refer to RULE #1