Engine Distribution Mechanism Repair and Maintenance Guide

The valve train parts as an important part of the engine, its service life should be consistent with the overall life of the engine, but often found in the use of gas distribution mechanism life is much lower than the overall life of the engine, especially the valve, valve seat, valve guide and other major parts of the short life, often in the second and third maintenance, part of the parts have exceeded the use of the pole and need to be replaced in advance, resulting in a great waste.

The Main Causes of Early Damage to the Gas Distribution Mechanism

Poor maintenance quality is a prominent problem in the maintenance operation is that the valve and valve seat working surface processing quality does not meet the requirements, resulting in early damage due to ablation and denting of the working surface; the camshaft bearing in the scraping of the clearance, contact area, concentricity of the bearing does not meet the requirements, accelerating wear, and early damage due to strange noise; valve guide in the replacement of new parts, reaming quality does not meet the requirements, which directly affects the Valve and valve seat life.

Improper application of maintenance data: maintenance can not scientifically select maintenance data is an important reason for early damage to the parts. Such as valve and valve seat contact surface width, the intake valve for 1 ~ 2.2mm, exhaust valve for 1.5 ~ 2.5mm. But in the maintenance, people tend to think a little wider than narrower insurance, used to choose the upper limit or close to the upper value, and thus just repaired the car valve working surface width is close to the use of the extreme. Another example is the valve foot clearance, general automobile regulations for 0.2 ~ 0.25mm, but in the maintenance and adjustment also mistakenly think that the gap is a little larger than a little better, therefore, over the upper limit use. In fact, the gap is too large, not only to reduce the engine power, and will also appear knocking sound and early damage.

Matters to Note in Maintenance

Gas distribution mechanism in the maintenance of more manual work, due to differences in technology and understanding of the differences in the maintenance personnel, the quality of maintenance is difficult to meet the requirements; therefore, in the maintenance of gas distribution mechanism should be particularly stressed in the quality of maintenance, and take effective measures to improve the quality of maintenance to extend its service life.

valve light grinding: in the maintenance operations, such as valve ablation, pitting and depression, should be light grinding. Usually in the valve light grinding machine, the operation should pay attention to four issues: First, to ensure that the valve head and rod concentric, otherwise should be straightened; Second, the amount of light grinding in the premise of grinding out the complete cone surface as small as possible; Third, try to improve the surface finish; Fourth, the valve rod end depression should be smoothed.
Valve seat reaming: valve seat reaming is usually manual work, should pay special attention to three issues: First, in the elimination of depressions, spots, can ream out the complete tapered surface on the basis of the smaller the better; Second, the reaming force should be uniform, the starting knife to close the knife to light, less reaming more observation, in order to ensure less reaming volume and higher finish; Third, with the valve test match, determine a good working surface location and width. The position should be adjusted to the lower middle of the valve cone, the upper or lower can be adjusted by the upper and lower mouth reamer. Working surface width, the intake door can be mastered in 0.9mm (1 ~ 2.2mm), the exhaust door can be mastered in 1.4mm (1.5 ~ 2.5mm). Practice has proved that the above width in the valve and valve seat grinding, the intake door up to 1mm, the exhaust door up to 1.5mm, are in the lower limit of the specified width, can greatly improve its service life.
valve grinding: valve grinding is divided into two cases, one is the valve and seat only a slight pockmark, do not need light grinding and reaming when grinding; second is the valve and seat have been light grinding and reaming after the grinding. The former first with rent diamond grinding, after grinding off the pockmark, then use fine diamond grinding, coated with oil grinding, until the seal meets the requirements, the width meets the provisions. The latter only when the seal does not meet the requirements of grinding, but the operation must be careful not to use excessive force, it is strictly prohibited to knock the valve up and down, otherwise there will be concave sand marks, affecting the quality of maintenance.
valve guide reaming: valve stem and valve guide with clearance is the key to determine the valve guide life, so when replacing the new valve guide, reaming should be strictly mastered with the clearance, the use of the lower limit of the specified clearance of each model, can effectively extend the service life.
Scraping of camshaft bearings: Scraping of camshaft bearings is a manual operation, and it is difficult to ensure quality. For the convenience of scraping, and usually outside the cylinder block processing, so should pay special attention to four issues.

First, to determine the diameter of the inner hole after bearing scraping (expressed in the formula: inner hole diameter = journal diameter measured value + with the lower limit of clearance + bearing and seat hole interference measured value);.

Second, scraping to try to maintain the coaxiality of the bearing bore and outer circle.

Third, while scraping with the journal test fit (at this time the clearance for the interference + clearance), and to ensure uniform distribution of contact marks;.

Fourth, when pressing the bearing into the seat hole, attention should be paid to aligning the oil hole. After scraping, install the camshaft, rotate it for several turns, and make appropriate trimming as appropriate, the contact area should reach more than 75% and be evenly distributed, and the clearance should be in accordance with the regulations.

Valve foot clearance adjustment: In normal use, the valve foot clearance will change as the parts of the air distribution mechanism wear. Such as cam, valve rod end face and tappet contact surface wear after the clearance will become large, and valve head and valve seat wear after the clearance and become small, therefore, in the adjustment should take the middle value of the clearance is appropriate. Therefore, the middle value of the clearance should be taken in the adjustment, such as 0.2~0.25mm, which can be taken as 0.22mm. This not only takes care of the actual situation of the clearance change, but also considers the measurement error, which can fully guarantee the realization of the valve foot clearance.

In addition, the maintenance of other components and parts of the air distribution mechanism is mainly to strengthen the cleaning and inspection of the parts, and the correct adjustment and assembly according to the regulations, in order to achieve its overall coordinated work.