Originally Posted by
wrench1
FYI: this is not the AD in question for the OP issue. There is no AD currently in the works but an SB in the works which will contain S/Ns. TCM came out with
a notice yesterday. Word is supposedly the retaining rings/circlips for the crankshaft dampener bushings/pins were orientated opposite of the installation requirements. If you want to see the area in question look in the old
SB 99-3 which addressed a different issue.
Given they have it narrowed down to less than 200 hrs TIS engines they probably have a good idea of what is the cause. Regardless, my guess there more to this than a reversed circlip as most have no specific orientation requirements.
The circlip seems to have a "sharp" and a "non-sharp" edge, where the sharp edge needs to be positioned "outwards", according SB 99-3. Mount it the other way around, and it'll probably get some slack, in the long run loosening up the balance weight mounting, in the end, destroying the engine, once one of the balance weights departs its mounting.
So, it could be, one specific mechanic did install the circlips consequently the wrong way around, and it seems to be known from experience, that the engine destroys itself within 200 TIS, when the circlip(s) is/are mounted wrongly.
Retrieve the engine serials this mechanic worked on, follow the delivery trail, and it is known which engines need to be opened up and potentially will need a crankshaft rebuild/revision. A complication can be, that crankshafts might be prebuilt/assembled, leaving the challenge, which crankshaft ended up in which engine. An issue is to reliable reach all aircraft owners/users with affected engines.