The kart’s transmission consists of a chain, gear wheel and sprocket. Elements that we all know but which, unlike other vehicles, for example bicycles or motorcycles, are subjected to greater stress due to the forces involved and the absence of flexible couplings. The common mistake is neglecting maintenance and not knowing how to recognize the alarm bells that necessitate the replacement of a worn component. It must be said that a transmission failure, for example the chain breaking, can also affect the engine. In the case of engines without a rev limiter, an overspeed could occur with consequent damage to the connecting rod which would therefore be replaced with certainly higher costs than those that can be incurred to keep the chain-gear wheel-sprocket fully efficient, thus reducing this type of fault and damage.
So let's see the correct procedures to always have an efficient transmission.
Two types of chains are used for karts, one for single-speed engines, called the 219 series, and one for the gear motors, the 428 series. The two types differ in the length of the wheelbase and internal width, but are composed of the same elements. In detail, the chains are composed of two parallel series of plates (internal plate and external plate) with two offset holes, connected by a pin. A bush is inserted around the pin which crosses the inner plate and allows lubrication along the pin. A roller is mounted on the bush, enclosed by the internal plates. The roller is the element that absorbs most of the force exerted by the sprocket to transfer it to the gear wheel teeth.
There are chains with O-rings between the inner and outer plates; this set-up allows continuous lubrication of the elements and prevents the penetration of external agents (dirt, earth, dust, etc.) which affect the duration of the chain. Chains with O-rings increase friction and reduce power to the wheel. These are low values, but their use is recommended with engines with powers above 30 HP, where the duration of the chain is put to the test. Conversely, in engines with less horsepower, for example in the single-brand or in the 60 cc of the MINI, a chain without an O-Ring is recommended, making the transmission smoother.
The 219 series chains are available in different lengths, depending on the number of links they are made of, generally from 98 to 110.
The chains used in kart shifters (428 series) have bigger links to withstand the forces to which they are subjected and can be modified in length by using a special tool on the connecting link, the chain extract and "chain mesh", to eliminate/add links. The junction mesh is recognisable due to the presence of a double external closing plate, which allows the opening and insertion of links to increase the total length. The variation is always of two meshes (a pair of internal plates and one of external plates). The chains have an even number of links.
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