ELBOW 3K6839 - Caterpillar

There are a number of factors that can affect the CO emissions output of an engine. Many of those factors are related to engine maintenance that prevents or eliminates water leaks in the prechamber. However, deposit build-up in the combustion chamber has been found to also increase the CO output of the engines. This deposit build-up generally cannot be eliminated until a top end overhaul is performed.
Engines within the first 1000 hours of operation should meet the previous CO values. However, as in-cylinder deposits build up with time, the CO emissions will increase. The new levels should provide adequate margin so that the CO emissions will not exceed the given value out to 20,000 hours. Doing a top end overhaul on the engine at the 20,000 hour point and cleaning the deposits from the cylinder should return the engine to near new engine CO emission level.
It is important to note that not all engines will actually ever reach the level of a new engine after top end overhaul. It will depend on individual deposit build-up in the engine, general maintenance and time on the engine. These new "Not To Exceed Values" are provided to give adequate margin to cover a wide variety of engines, maintenance practices, and applications.
If necessary, existing sites should actively pursue obtaining new site emission permits from the local air quality board of your state.