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TKART magazine Under Review | KK3 Shifter, the flagship engine (approved for 2023) of the Modena Engines range
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Giacomo Mantovani
28 April 2023 • 20 min. read
125 cc

The KK3 features a 54 mm bore for a 54.43 mm stroke and has a cylinder volume of 124.66 cm³.


It is a 2-stroke engine, like the vast majority of racing-type kart engines. It is powered by a fuel mixture, with a recommended lubricating oil percentage of 4%.


The starter is not of the electric type. In fact to start the engine you have to put it in second gear when stationary and then push the kart for a very few metres in order to rotate the rear axle and start it up.


The KK3 engine has a 6-speed sequential gearbox, derived from the KK2, its predecessor.


The engine was designed and built by Modena Engines for the FIA Karting Shifter, KZ and KZ2 classes. Its international approval (which you can find here) is valid for 3 years and enures participation in all types of events that follow the CIK-FIA regulations.

Since 2013, the year Modena Engines' adventure in karting began with the approval of the KK1 engine, the Italian company has never hidden its particular attention to the development of Shifter engines for the FIA Karting KZ and KZ2 classes. Despite having various Direct-Drive engines in its range, in fact, it is quite evident how over the years Modena Engines has allocated more and more resources and time in the development of the KK project, reaching, in 2023, the approval of the third engine of the product line, i.e. the protagonist of this article: the KK3. We had the opportunity to visit the company's headquarters, about 100 km from Rome, to analyse and find out which innovations were developed with the KK3 and which, instead, were the components borrowed from its predecessor KK2 (approved in 2019, which we have covered in the article “Under Review - The new KZ Modena Engines KK2”). The protagonist of the renewal process to which this new engine has been subjected is the Modena Engines R&D team, composed of three engineers and three engine mechanics. These technicians made use, for the design, construction and development of the KK3, of CAD (Computer-Aided Design) software, advanced CNC machinery (capable of ensuring the most modern machining) and test benches, to refine the work and define the best technical direction for developing the engine.

The general appearance of the KK3 is well-finished both in terms of the quality of the materials and design. Abundant veining, wide thicknesses of the coupling parts (to ensure sealing) and with the positioning of the various organs (for example, the axis of the crankshaft and the sprocket) that is very different than that of the previous KK2.
The KK3 weighs 19.5 kg, a value obtained thanks to the interesting developments undertaken compared to the KK2 model.
At the basis of the redesign process of the KK3 there was the renewal of some production processes, starting from the type of aluminium casting which, for the new engine of the Italian company, is seashell by gravity casting. This is carried out by an external foundry according to the specifications provided by Modena Engines.
This fusion methodology, thanks to the use of cores produced by "shell moulding", allows mass production with high precision to be obtained, even if it concerns a large number of complex pieces with an elaborate internal structure. Furthermore, it is a process which provides for a more rapid solidification of the metals and which is therefore able to give excellent mechanical qualities to all the components. Contrary to what happens with other types of casting (sand or die-casting), the shell process gives lighter products: it allows lower wall thicknesses to be obtained with a better aesthetic appearance, ensured both by a good surface finish and by a moderate dimensional accuracy. Once produced, the unfinished pieces are taken over by Modena Engines which carries out the 5-axis CNC machining internally, at its headquarters in Modena (Italy). Finally, all the components, including those made of plastic (such as the protective casings), pass to the final phase for the finishing of the holes and coupling surfaces in the machine.
The purchase kit of a Modena Engines KK3 includes: [1] the complete KK3 engine unit, [2] the two light U-bolts complete with screws for fastening the engine, [3] the gear lever, [4] the lowered spark plug, [5] the NGK R7282 10 spark plug, [6] the DELLORTO VHSH 30 carburettor, [7] the MIKUNI fuel pump, [8] the fuel pump support in laser cut sheet steel with screws and vibration dampers, [9] the exhaust expansion, [10] the exhaust “bend”, [11] the ELTO TD3 exhaust silencer, [12] the springs for the exhaust.
Although the KK3 has seen a profound renewal, which involved the type of aluminium casting and some innovative solutions, the new Modena Engines-branded power unit has inherited several components from its predecessor, the KK2 (in the picture). Specifically: the intake manifold, the reed valve pack, the gearbox unit, the primary transmission, including the clutch unit, and the combustion chamber with its dome.
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