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TKART magazine Under Review | Maxter KZ MXS 2. A lengthened connecting rod
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01 May 2016
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Like most kart engines on the market, the MXS 2 is a 2-S. 4-stroke engines are still a small niche

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125 cc has been the standard for some time now, while in the past it used to be 100 cc

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Push-mode as in all KZ engines, with hand-release clutch and neutral to 2nd gear shifting

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The MXS 2 belongs to the gearbox “family” of karting engines.
It has a 6 gear manual transmission

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Certified under KZ homologation, just renewed and valid for the next 9 years, beginning in 2016

Let’s take a look at the new KZ class engine manufactured by Maxter, the motorsport brand of the CRG group: the MXS 2. “2” indicates the new 2016 approval

Let’s start with the most important new feature: the lengthened connecting rod. This is the component around which the new KZ by Maxter, called the MXS 2, adapts a number of other components such as the cylinder, ports and ducts, exhaust, silencer and so on. According to the measuring tape, the new connecting rod goes from 110 mm to 113 mm in length. The goal is to improve midrange rotation, perhaps even at the expense of the high rotation range, to make the engine markedly more driveable, forgiving and suited to anyone. The intake duct has not changed on the MXS “2” series engine, nor has the reed valve pack, although the latter now features stiffening leaf springs that make the reed valves stiffer in the second part of the aperture. This further improves midrange rotation. The opposite is true of the cylinder that, with its new connecting rod, has also been changed, featuring modifications to ports, angles, transfer and exhaust ducts. The “restyling” also involved the cooling ducts, which have been modified to achieve more uniform temperatures and, consequently, steadier cylinder expansion in the various zones. All the above optimises the interaction between piston and cylinder and, therefore, improves engine performance and reliability. The cylinder head has also been changed and now has a new shape, with a sort of step in the middle.
The connecting rod goes from 110 mm to 113 mm. A choice made to improve performance at midrange rotations. The images show a comparison between the new connecting rod (on the right) and the old, shorter one (on the left)
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The cylinder (new model on the right, compared to the old one) features completely different ports, transfer ducts and angles to fit the new length of the connecting rod. The cooling ducts have also been optimised
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The cylinder head shape has been changed and now features a step, as can be seen in the comparison between the head on the previous engine (photo below, on the left) and the new one (on the right)
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The goal, yet again, is to improve delivery, in particular the torque and power curves that are now more uniform and no longer suffer “dips”, i.e. points at which delivery is not as strong.
As mentioned earlier, the first item in the design phase was the choice of the connecting rod length: 113 mm. The cylinder geometry was adjustment as a result and tests were carried out using the old silencer. The silencer itself was subsequently modified to optimise delivery and, as was the case for other parts of the engine, further improve the torque and power curves, without any “dips”.
On the exhaust system, the duct has also been changed, from a curved duct with a more rounded section, to a duct with an oval section and a straight shape. On the exterior of the engine, the mounting plate has been changed and is now more inclined so that the air filter is horizontal, with a greater intake of air and, therefore, improved performance. Being a KZ engine, changes to the gearbox area could not be overlooked. The shape of the selector may have remained the same, but significant changes have been made to the materials, featuring treatments for greater hardness and, therefore, extraordinary durability.


Maxter’s history is inextricably linked to CRG,...

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The reed valve pack is unchanged from the previous model, but the reed valves now feature stiffened leaf springs. This change is also aimed at improving midrange rotation performance
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The gearbox material undergoes new heat treatment and is now harder and more durable. The images show a comparison between the old model, on the left, and the new one, on the right
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The silencer is new and optimises the power and torque curves
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