Connecting rod in the kart

Connecting rod is a fundamental component of the engine, being part of the crank gear that is able to transform the reciprocating motion of the piston into the rotating crankshaft motion.. Due to the considerable entity of the inertia forces, connecting rod is a very stressed mechanical element and then it must have excellent mechanical properties. Connecting rod failure can in fact have disastrous consequences on engine and it must be absolutely avoided.
Connecting rod manufacture process vary as a function of the specific kind the application the component will be used on and, in particular, on the revolutions per minute of the particular engine. Higher revolution speeds involve higher inertia forces and then higher stresses in the connecting rod; is then necessary to trim the manufacture process in such a way to give to the component the needed mechanical strength. Another fundamental aspect is the geometrical and dimensional precision that can be obtained from a fabrication process and, in particular, parallelism condition between the two connecting rod axles, on which errors must be lower then 0.1 mm. It’s then clear how high performance applications need very tight tolerances while a lower manufacturing precision can be adopted in those fields characterized by lower engine rotation regimes.
Connecting rods can be obtained by foundry, sintering or forging, and in this last way the best features can be obtained. Forged connecting rods are then used in high performance automotive and motorcycle applications.
Connecting rods obtained by foundry are instead use on common automotive applications, while punched rods are used for agricultural engines.
Aside from the manufacturing method used to produce the raw piece, this is always subject to a series of operations until the realization of the finished product. In particular, the rod is first cut to obtain the rod head and then the needed profiles are realized on the rod sides by milling.
Then the connecting rod is drilled to obtain the holes on the head and on the basis and finally, by milling are created the planes on which the screw used for the connection of the two rod parts will be hosted.
Usually, steel with good fatigue strength is adopted for the production of connecting rods (fatigue is the primary cause of connecting rods failure ). Typically Chromium-Molibdenum steels are used, with various alloy elements, and the mechanical resistance is improved by means of sanding or shot blasting operation.


Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma

renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com

Phone +39 0672597136