CFM International has frozen the design of the Leap-1B engine for the Boeing 737 Max.
The manufacturer said during a briefing in London that the freeze was achieved "on time" on 29 April.
It says this will allow the manufacturer to begin releasing parts for the first engine to test.
CFM's schedule shows it will produce the first -1B test engine by mid-2014.
Leap programme manager Gareth Richards says assembly of the first Leap engine "of any kind" began last week. The manufacturer will initially produce test versions of the Leap-1A for the Airbus A320neo and then the Leap-1C for the Comac C919.