Design, maintenance of the MAZ car frame
The frame of the car is riveted, consists of two longitudinal beams (spars) of a channel shape with a variable section, made of strip low-alloy steel 22G2TYu 8 mm thick
The frame spars (the largest section size Z10x85), made by hot stamping, are connected in five places by cross members using rivets.
Stamped low-alloy steel crossbars, second and third mild steel.
The brackets of the front, rear and additional springs, side engine mounts, cab mounts, steering, etc. are attached to the spars.
A design feature of the frame is the transfer of the fastening of all its power elements, and in particular the brackets of the springs and cross members, to the vertical walls of the spars in the most loaded places.
The use of high-strength low-alloy steel, the absence of rivet joints on the lower flanges of the side members made it possible to favorably distribute stresses and achieve high frame strength.
Care of the frame consists in checking the bolted and riveted connections.
During the operation of the car, it is necessary to ensure that the geometric shape of the frame, the correct position and strength of its spars, crossbars and brackets are not disturbed.
Violation of the geometric shape of the frame can lead to an incorrect position or displacement of vehicle components, which will cause excessive stress and increased wear on transmission and engine parts.
Loose rivets are detected by a rattling sound when the rivet head is tapped with a hammer.
Rivets that are loose must be cut down and replaced with new ones.
There should be no unpainted spots on the frame, as this can lead to corrosion, which reduces the fatigue strength of the frame.
Therefore, the frame must be periodically cleaned, inspected and painted over bare and corroded areas.
The main defects of the frame can be: cracks in the side members and cross members, loosening of rivet joints, wear of the spring brackets, longitudinal cracks in the side members in the area of the rivets.
Cracks in spars and cross members are repaired by welding. Before welding, the crack must be cut with an emery wheel at an angle of 75 - 90˚.
It is recommended to use arc welding with electrodes designed for low alloy steel.
If there are cracks on the shelves that do not extend to the wall of the side members, in addition to welding the crack, install reinforcing plates made of low-alloy steel 8-10 mm thick on the inside or outside, which are welded with longitudinal seams and riveted with electric rivets.
Welding should be carried out in accordance with the sketches (Fig. 2, a, b).
If the cracks go to the wall of the spars, then, in addition to welding the crack itself, install an L-shaped reinforcement with its subsequent welding (Fig. 2, c).
The frame is allowed for repair if there are no more than two cracks on one side member, reaching the middle of the profile.
A frame that has more than two cracks on each side member reaching the middle of the profile, or one or more cracks on one of the side members passing beyond the middle of the profile, cannot be repaired and must be replaced with a new one.
Rivets with broken heads are knocked out and replaced with bolts (if necessary, oval holes are expanded).
When cracks appear in the spars (no more than 3) from under the rivets, the end of the cracks is drilled with a drill with a diameter of 5-7 mm in order to prevent their further propagation. In this case, welding is not required.
If, when checking the riveted joints of the frame, a breakage of the rivet head is detected, then it is necessary to knock the rivet shaft out of the hole and install a new rivet.
Instead of a rivet, it is allowed to install a heat-treated bolt with a nut and a spring washer of the appropriate diameter, ensuring the tightening torque of the M16x1.5 nuts - 200 - 240 Nm (20-24 kgcm) and the M14x1.5 nuts - 160 - 180 Nm (16 - 18 kgcm ).
The fit of the bolt in the hole must be tight.