What are the main contents of automobile engine camshaft maintenance?


What are the main contents of automobile engine camshaf […]

What are the main contents of automobile engine camshaft maintenance?

The camshaft is an important part of the engine valve organization. In order to ensure that the engine can inhale fresh air on time and discharge the burned exhaust gas in time, the camshaft acts as the driving valve to open and close on time, and some camshafts also have the function of driving the distributor to roll. The speed of the car engine is very high. In order to ensure the efficiency of intake and exhaust, the valve adopts an overhead design, and the camshaft drives the valve action through hydraulic tappets. How to overhaul the camshaft of an engine?

(1) Inspection and adjustment of axial clearance
When checking the axial clearance of the engine with thrust flange for axial positioning, insert a feeler gauge between the front end face of the camshaft first journal and the thrust flange or between the end face of the timing gear hub and the thrust flange. The thickness value of the feeler gauge is the axial clearance of the camshaft. Generally, it is 0.10mm, and the use limit is 0.25mm. If the open space does not meet the requirements, it can be adjusted by increasing or decreasing the thickness of the thrust flange.

(2) Inspection of camshaft bending deformation
The bending deformation of the camshaft is measured by the radial runout error of the camshaft center journal to the two end journals. Place the camshaft on the V-type iron, and place the V-type iron and dial indicator on the flat plate, so that the dial indicator contact is perpendicular to the camshaft center journal. Roll the camshaft and observe the swing of the dial indicator needle is the curvature of the camshaft. After the inspection is completed, the inspection results are compared with the specification values ​​to determine whether to repair or replace.

(3) Other maintenance items of camshaft
1) Maintenance of the keyway of the timing gear journal: The symmetrical plane of the keyway of the timing gear journal should generally coincide with the symmetrical plane of the intake and exhaust cams of the first cylinder to the large lift, and its wear will change the valve timing. After the keyway is worn, the keyway can be re-opened by surfacing welding or another keyway can be opened in a new position.

2) The limit wear of the eccentric driven by the gasoline pump: the limit wear of the eccentric driven by the gasoline pump is generally 1mm. If the limit is exceeded, the camshaft should generally be replaced.

3) Maintenance of cam wear
The wear of the cam changes the lift rule of the valve and reduces the maximum lift, so the maximum lift reduction value of the cam is the main basis for the cam inspection and classification.
When the reduction value of the cam to the maximum lift is greater than 0.40mm or the cumulative wear of the cam surface exceeds 0.80mm, the camshaft is replaced; when the cumulative wear of the cam surface is less than 0.80mm, the cam can be ground on a camshaft grinder.
However, the cams of the camshafts of modern automobile engines are all combined line types. Due to the extremely high machining accuracy and high repair costs, they are rarely repaired now, and the camshafts are generally replaced.

4) Overhaul of camshaft journals and bearings
① Maintenance of camshaft journals and bearings: use a micrometer to measure the roundness error and cylindricity error of the camshaft journal. The roundness error of the camshaft journal shall not exceed 0.015mm, and the coaxiality error of each journal shall not exceed 0.05mm. Otherwise, the repair ruler should be used.

② Overhaul of camshaft bearings: When the cooperative space of camshaft bearings exceeds the limit of use, new bearings should be replaced.

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