Transmission gears frequently operate under constantly fluctuating speeds and loads; furthermore, their tooth surfaces are subjected to impact loads, leading to damage to the gears (particularly their tooth surfaces). Common forms of damage include:
(1) Gear Wear: Under normal operating conditions, transmission gear tooth surfaces exhibit uniform wear. It is required that wear along the tooth length direction does not exceed 30% of the original tooth length, and wear on the tooth thickness does not exceed 0.40 mm. The effective gear meshing area must cover no less than two-thirds of the tooth surface. The meshing clearance for constantly rotating gears should generally be between 0.15 and 0.26 mm, with a service limit of 0.80 mm; for engaging gears, the meshing clearance should be between 0.10 and 0.15 mm, with a service limit of 0.60 mm. These clearances can be measured using a dial indicator or the soft-metal impression method. If the clearance exceeds the specified limits, the gears should be replaced in pairs.
(2) Broken Gear Teeth: Broken gear teeth are primarily caused by improper gear meshing clearances, misalignment of the meshing contact points, or exposure to significant impact loads during operation. If there are minor chips (no larger than 2 mm) on the edges of the gear teeth, they may be smoothed down with an oilstone and the gear reused; however, if the damage exceeds this limit or if there are more than three such minor chips, the gears must be replaced in pairs.
(3) End-Face Wear on Constantly Meshed Gears: Constantly meshed helical gears require an axial clearance of 0.10 to 0.30 mm at their end faces to ensure smooth operation. If the gear end faces show signs of grooving due to wear, they may be restored by grinding; however, the total amount of material removed by grinding must not exceed 0.50 mm.
(4) Wear on Journals, Needle Bearings, and Housing Bores of Constantly Meshed Gears The clearance between the gear bore, the needle roller bearing, and the journal must be within the range of 0.01–0.08 mm; otherwise, the components must be replaced.
Inspection and Repair of the Transmission Housing
The transmission housing serves as the foundational component of the transmission assembly; it ensures the correct positioning of all internal parts and bears specific loads during operation. Common forms of damage include:
(1) Wear of Bearing Bores: Wear in the housing's bearing bores disrupts the proper fit between the housing and the bearings, thereby directly affecting the relative alignment of the transmission's input and output shafts. The clearance between the bearing and its bore should be 0–0.03 mm, with a maximum allowable service limit of 0.10 mm. If this limit is exceeded, the housing must either be replaced or repaired by installing a bushing insert into the bearing bore.
(2) Repair of Threaded Holes in the Housing: Damage to the threads of the oil filler plug hole, the oil drain plug hole, or the threaded holes for the housing-to-housing connecting bolts can be repaired by installing a threaded insert (repair plug).
Inspection and Repair of Transmission Shafts
During transmission operation, the various shafts are subjected to fluctuating torsional moments and bending moments. Common forms of damage to these shafts include:
(1) Journal Wear Excessive wear on the journal not only causes the gear axis to shift but also alters the gear meshing clearance, resulting in noise during power transmission. Furthermore, it compromises the fit between the journal and the bearing, potentially leading to seizure during operation. Therefore, the wear on the journal at the interference-fit location for roller bearings must not exceed 0.02 mm, and for needle bearings, it must not exceed 0.07 mm; otherwise, the component must be replaced or repaired via chrome plating.
(2) Spline Wear: Wear on the splines is typically more severe on the load-bearing side. Inspection should be performed by fitting the gear onto its corresponding spline sleeve. If the spline wear exceeds 0.25 mm, or if the clearance between the spline and the original keyway exceeds 0.40 mm-or, in the case of the gear's engagement teeth and coupling sleeve, if the circumferential clearance with the splines exceeds 0.30 mm-or if the clearance between a semicircular key and the journal keyway exceeds 0.08 mm, then the splined component or the shaft containing the keyway must be repaired or replaced.
(3) Transmission Shaft Straightness Inspection: Support the transmission shaft at both ends using the center holes (center points) and employ a dial indicator to check for radial runout. The deviation should be less than 0.10 mm; if it exceeds this limit, the shaft must be repaired via pressure straightening.
Synchronizer Inspection and Repair
a. Lock-Ring Type Inertia Synchronizer: The cone angle (α) of the lock ring is approximately 6° to 7°. During operation, if the cone angle deforms and increases-preventing rapid synchronization-the lock ring must be replaced immediately.
b. Lock-Pin Type Inertia Synchronizer: The primary failure modes for the lock-pin type synchronizer involve wear on the cone ring and cone disc. If the 0.40 mm deep helical grooves on the conical surface of the cone ring wear down to a depth of 0.10 mm, the cone ring must be replaced. If the end face of the cone ring exhibits scoring or scratches, it may be repaired by facing on a lathe; however, the cumulative material removed during facing must not exceed 1 mm; otherwise, the cone ring must be replaced.