How to overhaul the engine camshaft?
The camshaft is inspected from three aspects: inspection and adjustment of axial clearance, inspection and repair of camshaft bending deformation, and inspection and repair of other cam wear. The third aspect is divided into inspection and repair of camshaft journals and bearings.
（1）Check and adjust the axial clearance
When checking the axial clearance of an engine that uses a thrust flange for axial positioning, insert a feeler gauge between the front end face of the first journal of the camshaft and the thrust flange or between the end face of the timing gear hub and the thrust flange. The thickness of the feeler gauge is the axial clearance of the camshaft. It is generally 0.10mm, with a maximum limit of 0.25mm. If the clearance does not meet the requirements, it can be adjusted by increasing or decreasing the thickness of the thrust flange.
（Intake camshaft Audi Volkswagen EA888 CEAA 06J109022G）
（2）Inspection and repair of camshaft bending deformation
The bending deformation of the camshaft is measured by the radial runout error of the camshaft middle journal to the journals at both ends. The inspection method is shown in the figure. Place the camshaft on the V-shaped iron, and the V-shaped iron and the dial indicator on the flat plate, so that the dial indicator contact is in vertical contact with the camshaft middle journal. Turn the camshaft and observe the swing difference of the dial indicator needle, which is the bending degree of the camshaft. After the inspection is completed, compare the inspection results with the standard value to determine whether to repair or replace.
（​Intake camshaft Toyota Lexus 2AZ-FE 13501-28060）
（3）Other camshaft maintenance items
1) Inspection of the timing gear shaft journal keyway: The symmetric plane of the timing gear shaft journal keyway should generally coincide with the symmetric plane of the maximum lift of the first cylinder intake and exhaust cams. Its wear will change the valve timing. If the keyway is worn, it can be reopened by surfacing welding or opened at a new position.
2) The maximum wear of the gasoline pump drive eccentric wheel: The maximum wear of the gasoline pump drive eccentric wheel is generally 1mm. If it exceeds this limit, the camshaft should be replaced.
（Camshaft Intake Mitsubishi 4A92 MW252324）
Diameter runout value: standard - 0.01 ~ 0.03 mm, limit - 0.05 ~ 0.10 mm.
3) Inspection and repair of cam wear
When the maximum lift reduction value of the cam is greater than 0.40mm or the cumulative wear of the cam surface exceeds 0.80mm, the camshaft should be 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 modern automobile engine camshafts are all combined linear types. Due to the extremely high processing precision and high repair cost, they are rarely repaired at present, and the camshaft is generally replaced.
（Camshaft Intake Mitsubishi 4A92 MW252324）
4) Inspection and maintenance of camshaft journals and bearings
â‘ Inspection of camshaft journal and bearing: Use a micrometer to measure the roundness error and cylindricality error of the camshaft journal. The roundness error of the camshaft journal shall not be greater than 0.015mm, and the coaxiality error of each journal shall not exceed 0.05mm. Otherwise, it should be repaired according to the ruler.
â‘¡ Inspection of camshaft bearing: When the matching clearance of the camshaft bearing exceeds the use limit, a new bearing should be replaced.
（Exhaust Camshaft Toyota Lexus 1AZ 2AZ 13502-28030）
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