COVER 6Y0728 - Caterpillar

3406 ( 4FD, 1RK );
3408 ( 6NB );
3412 ( 7DB ) Spark-Ignited EnginesSUPPLEMENT: 10/14/91Service Magazine; September 9, 1991; Page 11; "New Camshafts Provide Increased Power, Reduced Fuel Consumption, Reduced Exhaust Temperature, And Reduced Emissions" from 3406, 3408, and 3412 Spark-Ignited Engines.The article was not complete. Add the information that follows to the end of the article. The Chart A lists the new and former camshaft assembly part numbers. Chart B lists the effectivity of the new camshaft assemblies.
--------------- END SUPPLEMENT ---------------New camshafts are used. They are the "early inlet closing" (EIC) camshafts and the "low overlap" (LOL) camshafts. The EIC camshaft closes the inlet valve before the piston reaches the bottom of its stroke. The LOL camshafts provide increased lug capability.
The new EIC camshaft is used in high speed (1800 rpm) engines and on the 3406 low speed (1000-1400 rpm) engine when "low compression ratio" (LCR) is required. The former high speed, LCR 3408 and 3412 engines used an 8.5:1 geometric piston and a standard camshaft. Now, the high speed 3408 and 3412 engines use the EIC camshaft, and the same piston (9.7:1 geometric) as the former high compression ratio engine. The 3406 LCR engine uses the EIC camshaft and 10.3:1 compression ratio piston. The early closing of the inlet valves provide an effective 8.5:1 compression ratio on the 3408 and 3412 engines and an effective 9.4:1 compression ratio on the 3406 engine. When compared to the standard camshaft and LCR pistons, the combination of the EIC camshaft and 9.7:1 compression ratio (10.3:1 compression ratio on 3406 engine) piston provide reduced fuel consumption, increased horsepower at rated speed, and lower exhaust temperatures.
The low speed (1400 rpm) 3408 and 3412 engines use the LOL camshafts and the 8.5:1 (geometric) compression ratio pistons. The 3406 low speed engine uses the EIC camshaft and 10.3:1 compression ratio piston, or the LOL cam and 10.3:1 compression ratio piston.
In generator set engine applications, engines with LOL camshafts provide ISO Class II respons. In industrial engine applications, engines with LOL camshafts provide increased lug capability.