Piston fingers
The piston pin is an element of the crank mechanism of cylindrical shape, which is the axis of movement of the connecting rod at the point of its connection with the piston and thus provides a movable hinged connection of the head of the connecting rod and the piston.
In the process of engine operation as a piston, and the piston pin is subject to severe loads. The finger is affected by the pressure on the compression stroke of the fuel-air mixture, the force of expanding gases after ignition, inertia, bending effort, etc.. Taking into account such loads, the material of the piston fingers is hardened steel. Forced engines in comparison with regular versions receive a piston pin with a harder surface of alloy steel.
Structurally, the piston pin has an internal hole to facilitate the part. Low weight means reduced inertial losses and increased engine efficiency. The finger must remain strong and durable under extreme loads. In mass production, the hole of the piston pin has a simple cylindrical shape. This solution reduces costs in the manufacturing process.
Another option for the inner hole of the finger is to make open outside cones (variety with or without conical jumper). The cones narrow in the middle of the piston pin.
Such solutions allow you to effectively reduce the weight of the part and maintain the required strength, but have a high cost for mass production. For this reason, fingers of this type are usually placed on sports and boosted engines, in the manufacture of which the final cost of manufacture is of secondary importance.
There are two types of piston fingers according to the method of installation:
- fixed piston pin;
- floating piston pin;
The fixed finger provides a tight fit in tension for reliable axial fixation. This mounting means no finger rotation at the installation site (the upper head of the connecting rod or the holes of the piston bosses).
The fixed connection is usually realized in the upper head of the connecting rod. The piston pin with this method of attachment rotates in the holes of the piston lugs, where a certain gap is provided. Installation of the fixed piston pin during repair of the internal combustion engine becomes possible after considerable heating of a rod.
Floating finger means installation of a part with a certain gap as in the upper head of the connecting rod, and in the piston bosses. Fixation of the piston pin in this case is realized by means of special locking rings.
These locking rings of the floating piston pin are installed in the grooves, which are made in piston bosses. Also in motors with a floating piston pin in the upper head of the connecting rod is additionally installed ??bronze sleeve to minimize friction.
Floating piston pins need lubrication, as the hinge area with the connecting rod head is heavily loaded. The connecting rod head and the head sleeve have a special hole, through which engine oil penetrates from the inner cavity of the piston. As for the specified cavity, the oil is supplied there from the oil-bearing piston rings through special holes in the piston or can be injected by means of oil injectors of the engine lubrication system.
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