Joining the freewheel club is like joining the caterpiller club, frightens the living @@@@ out of you and you're lucky to live thru it.
Basically the donk goes to valve bounce speed instantly, which is deafening and it feels like you have stepped into a lift that is not there.
In my instance (a bell 47 3B1) I tried to re-engage twice from eighty feet, just after translating in a ten knot downwind at the time, just bent the skids and plucked the rear short shaft out due to deliberate bottoming of collective to avoid going over a cliff in front of me, that is when the freewheel re-engaed as if nothing was wrong. We put a short shaft into it and flew it home, the engine became a tin mine in seventy hours.
snap re-engagements we believed, a) will do lots of damage and can b) break the inner race.
Rule of thumb - always check free wheels GENTLY, so as they can demonstrate that they will work without duress and NEVER snap them back on. like anything mechanical.
I do believe that many earlier freewheel slips (Nigel ?)may have been put down to clutch slips until someone started pulling them apart with a micrometer. Although the heavy weight F/W was a relatively recent addition.
We found that a freewheel that did not engage on start up was a warning sign. I have yet to see evidence of heat on a clutch drum that would indicate clutch slip.
There are three types of '47 freewheels, lightweight, which is all that's called up for the KH4, and of course the G2 range.
Medium weight which is a wider and a bit heavier unit and the heavy weight, which is distinguished by the extra ring visible on the exterior on xmon which has holes all the way round on outside. Heavy model has extra planetaries as well.
use heavyweight only, read the worksheet from a trusted engineer that miked the rollers and inner and outer race within limits, fly within the hour limits and do a proper 600 hrly inspection and they will never fail.
Put a leightweight on a KH4, which is turbo charged and will pull much more power than a leighweight can handle and you will find the limit when you least expect it.