'''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-stroke 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 cm<sup>3</sup> 600GS. The basic LC4 design has gone on to power a range of KTM Motorcycles.<ref>{{cite web|url=https://www.ktmworld.com/blog/blog/2025/08/21/ktm-lc4-history-engines-evolution-and-enduring-legacy|website=KTM World|title=KTM LC4 HISTORY: ENGINES, EVOLUTION, AND ENDURING LEGACY |author = Ron Lieback|date=21 Aug 2025|accessdate=19 May 2026}}</ref>
== History == The LC4 engine has increased in displacement over the years. The original 600 (553 cm<sup>3</sup> actual) gave way to the 620 platform (609 cm<sup>3</sup> actual) which became the 640 series (625 cm<sup>3</sup> actual) from 1999 onward, then on to the 2008 version of the 690 (654 cm<sup>3</sup> actual) the 690 v2 (690 cm<sup>3</sup> actual) to its current 690 v3 (693 cm<sup>3</sup> 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
{{See also|KTM 690 series}}
===2019=== KTM introduces twin balancer shafts with the 690 LC4.<ref name=powerhouse/>
===2026=== KTM releases the significantly redesigned 690 LC4 increasing the displacement to {{cvt|692.7|cc|cuin}} with an increases to {{cvt|77.9|hp|kW}} @8000 rpm and slightly reduced {{cvt|53.9|ftlb|Nm}} 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.<ref>{{cite web|url=https://www.advpulse.com/adv-news/2026-ktm-690-enduro-r-unveiled/|website=ADV Pulse|title=KTM Unveils Specs And Availability Of Revamped 690 Enduro R |author = ADV Pulse Staff|date=13 Aug 2025|accessdate=19 May 2026}}</ref><ref name=powerhouse>{{cite web|url=https://livingwithgravity.com/ktms-new-single-cylinder-engine-innovations-and-strategic-positioning/|website=Living with Gravity|title=KTM's New Single-Cylinder Engine Innovations and Strategic Positioning|author = Vivek Sharma|date=20 Sep 2025|accessdate=19 May 2026}}</ref>
== LC4c== {{See also|KTM 390 series}} In the 2023/24 timeframe KTM designated their new 398.6 cm<sup>3</sup> motor LC4c.
== References == <!-- See https://en.wikipedia.org/wiki/Help:Referencing_for_beginners on how to create references. --> {{Reflist}}
== External links == *{{Citation |website=Ducati.com|title=The most powerful single-cylinder in the world |url= https://www.ducati.com/ww/en/company/innovation/engines/superquadro-mono|accessdate=19 May 2026}} *{{Citation |title=Here's how KTM built the world's most powerful single-cylinder engine for a road-legal motorcycle |url= https://www.motorcyclenews.com/news/new-tech/2025/september/ktm-690-smc-r-engine-tech/|date=10 Sep 2025|author=Nye Davis}}
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