Simply not true. There is play in the gears which is required to run properly, that play is the reason why they will not transmit harmonics of the crank.
This is a quote from Pete Jackson Gear drives Q&A section.
Fiction mixed with fact : Gear drives create harmonics
Fact : Every rotating part that contacts another, or part that is
stressed under load in an engine ( crank, cam, valve train,
gears, chains etc. ) creates a harmonic ( frequency ) . Some
frequency are harmless, a simple matter of unavoidable
friction , while other are percussive & concussive, and are
capable of creating damage in very short periods of time .
Gear drives, chains ( yes chains ) and most valve train
components create frequencies which are a simple matter
of friction and rendered harmless by simple lubricants (oil).
An unbalanced or improperly balanced crank , ( especially
if the harmonic balancer is removed ) create the percussive
and/or concussive types which can over a period of time
( if severe very short ) cause damage , above and beyond
anything considered normal wear . Gear drives absolutely
do not create these types of harmonics .
I never said they cause harmonics nor did I question there reliability. All I said is a belt drive may do the job with out the harmonics (transmited) by a gear drive.