Life span do not define class. It is thrust parameters and dimensions which define the class.
Life span depends on the metallurgy, engine design and number of engine cycles.
Western engines use better metallurgy and their engines are well designed to cater high heat stress.
In addition to this they do serialized tracking of every part to determine MTBF of that part. Data collection and its analysis helps them to isolate critical parts and reasons of failure. Upgradation or redesigning is subsequent result. This trend is more obvious in US systems. Other western systems and Russians are not that thorough.
Service life recommended by manufacturer was around 4000 hrs for RD-93, but our engineers at overhauling facility can give life extension to the engine modules, after replacing the damaged critical parts, for another 500 or 1000 hrs. And this process may continue depending on the overall condition of that particular module. After all PAF have so many highly qualified engineers and highly skilled technicians.
I was not implying that lifespan is dependent on different classes.
Just replacing parts will not increase lifespan as manufacturer lifespan takes that into account.
Pakistan has been using JF-17 since 2007 and so that is 13 years. Assuming 200 hours per year, then the oldest JF-17s will have gotten 2600 hours of engine use. There is no way that Pakistan can assume 7000 hours of total engine lifespan when it's most used engines may have only done 1/3rd of this amount and the earliest JF-17s may already have had new engines put in.
Edit - Just checked and it looks like the RD-33 series have 4000 hours service life but the RD-93 has been decreased to 2200 hours as increase in thrust has reduced service life.
As a rule of thumb:
Chinese engine lifespan - 1
Russian engine lifespan - x2
Western engine lifespan - x 4
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