KTM LC4 Engine is series of single cylinder engine designs produced by KTM debuting in 1987. "LC" in the name stands for Liquid Cooled while 4 indicated a 4 valve motor. Starting development in 1982 it was designed to replace air-cooled 4-strokes with an eye toward future emission standards. The first engine introduced was the enduro racing 553 cm3 600GS. The basic LC4 design has gone on to power a range of KTM Motorcycles.
History The LC4 engine has increased in displacement over the years. The original 600 (553 cm3 actual) gave way to the 620 platform (609 cm3 actual) which became the 640 series (625 cm3 actual) from 1999 onward, then on to the 2008 version of the 690 (654 cm3 actual) the 690 v2 (690 cm3 actual) to its current 690 v3 (693 cm3 actual) size.
Used in various KTM models the LC4 equipped bikes have had various engine size related designations:
1987 - 600GS 1994 - 620 Duke 1997 - 620 EGS/Adventure 1998 - 640 Supermoto 1998 - 640 Adventure-R 2008 - 690 Enduro R Other Variants include multiple Badge engineered models
2019 KTM introduces twin balancer shafts with the 690 LC4.
2026 KTM releases the significantly redesigned 690 LC4 increasing the displacement to with an increases to @8000 rpm and slightly reduced of torque @6750 rpm. KTM made these changes, reclaiming the “world’s most powerful” single-cylinder title, in response to the announced specifications for the Ducati Superquadro Mono.
LC4c
In the 2023/24 timeframe KTM designated their new 398.6 cm3 motor LC4c.
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