Background and Development of the KOMET K71 Karting Engine
Late 1950s through mid-1970's.
During the formative years of the competitive karting sport in the 1950's, many different engine prototypes were developed and tested, but without question, the early power plants developed by the McCulloch Corporation emerged as the most popular choice among racers and remained the front-runner for almost twenty years. When McCulloch announced they were halting production of their kart engine line in 1977, a scramble began for a suitable heir.
Following McCulloch's withdrawal one year earlier, the Yamaha Corporation entered the market in 1978 with what would be the first of many piston-ported engine designs. This new model was known as the KT-100. Within a few years, several other manufacturers introduced similar designs: next came the T-72 from DAP in Italy, followed by the TKM-BT82 from the Talko Corporation in England and the PCR PP100 from Italy.
As the popularity of piston-ported engines continued to rise, a new prototype—the KOMET K71—was developed in a joint effort between Italian American Motori Engineering (IAME) head engineer Renato Azzolini of Zingonia, Italy and IAME USA importer Lynn Haddock of Chattanooga, Tennessee. Mr. Haddock conceptualized the engine and Mr. Azzolini worked in conjunction with the IAME product development team in Italy to build the first prototype.
The K71 engine was designed to maximize performance while complying with existing North American Karting Technical Committee (NAKTC) guidelines for piston-ported engines. Its design incorporated two innovative changes from previous 100cc piston-port models: the addition of large 135cc main bearings, and a billet-slotted connection rod with lower rod centering. The engine was also the first to be built using heavy-duty components that were considerably stronger than was necessary to handle the engine’s power output. This upgrade resulted in an engine that was able to perform for very long time intervals before needing maintenance.
The original prototype for the K71 was prepared by using castings from the Komet K30, which was a 135cc rotary valve kart engine. For the crankcase, two magneto side castings were utilized. This allowed for the incorporation of the larger 6205 sized main bearings. A special liner fabricated from a solid sleeve was adapted to fit the old K30 cylinder barrel casting. The area needed for the inlet port was cut from a solid block, and was bolted to the casting to provide a mounting area for the carburetor. The head casting from the K30 was used, and needed only to have the bolt holes repositioned and a small mechanical change to the combustion chamber. The crankshaft was developed from a totally new design (without plastic stuffers) and was fabricated as a one-off unit for testing. It utilized a billet 96mm connection rod from the IAME racing department’s international Komet rotary valve kart engine program. The piston assembly was adapted from a Yamaha bike engine and featured two rings. For the ignition, a then-state-of-the-art Motoplat unit was imported from Spain.
The prototype engine was assembled, prepared, and tested extensively on the dyno at the IAME facility in Italy. It was subsequently shipped to the United States for track testing. The Moroso Road facility in southern Florida was chosen for its warm winter weather and considerable privacy. A test was arranged in conjunction with Bill and Todd Spaude, who provided all necessary equipment. The results from track testing were very positive, and the decision was immediately made to move forward with the approval process through the NAKTC, which was supported by both the International Kart Foundation (IKF) and the World Karting Association (WKA) at the time. Shortly thereafter, provisional approval was given, and mass production of the K71 began at the IAME facility in Italy. Following final counts and inspection, the new engines were cleared for distribution into the market.
The first race featuring the K71 was held at the Daytona International Speedway in Florida, and the success of the new design was confirmed immediately, as teams utilizing it dominated in every eligible class. Over the coming months and years, the K71 program’s success in the piston-port arena would continue throughout all divisions of kart racing in both the United States as well as in Europe, where the FIA-CIK (the European karting organization) adopted the piston-port design for its international junior racing class.
By the early 1990’s, reed valve engines began to gain popularity over the older piston-port design in the American market, and the K71’s use began to decline. Many distributors stopped carrying the engine and it appeared that the K71 was beginning to fade into karting history.
However—in 1996—the Horstman Manufacturing Company of California began importing the K71 as a component of their newly introduced “spec racing kit.” The Haddock/IAME engine design was retained and paired with a Horstman-manufactured low engagement centrifugal dry clutch and a spec exhaust system produced by RLV of California. The complete package was marketed as the Horstman Piston Valve (HPV) kit. The concept was a success, and was embraced by the IKF, the WKA, as well as many other regional and local kart racing organizations.
Production, distribution, and use of the HPV engine kit continued until October 2009, when IAME in Italy terminated its relationship with Horstman and appointed K71 engine designer Lynn Haddock (of Haddock Limited, Inc. in Chattanooga, TN) as the sole US distributor of the KOMET program. This action was in response to rising concerns over product availability and the deteriorating relationship between IAME and the leading US kart racing organizations.
Shortly after taking over the program, Haddock Limited introduced a new clutch system for the K71, which is also manufactured by IAME in Italy. The exhaust pipe kit continues to be produced by RLV in California.
Today, the K71 engine package continues its long history of success in the spec-racing arena under its new name—KOMET—and continues to build on its excellent reputation as a strong and reliable power package with very low associated maintenance and operating costs.