Inspecting valve springs

Inspecting valve springs have three measurements: spring height check, checking for squareness, and measuring the installed pressure. A deformed spring leads to wear of the valve stem and guide.

The valve spring must have the appropriate size and thrust, as this depends on the safe closing of the cylinder and the efficient operation of the engine. The springs must close the valves quickly and firmly. That is why it is important to check the condition of the valve spring during the overhaul of the cylinder head and determine that they meet the set specifications before they are reassembled.

Valve spring tester

By measuring the height of the spring, it is checked whether the spring has the correct height and that there is no fatigue of the material. The height deviation from each other must not exceed 1 mm.

Checking for squareness is a test of the general condition of the spring to compress and load the valve evenly during operation. The spring is placed on a perfectly flat surface and a try square is placed next to it. Rotate the spring around its axis to check for deformation. When there are irregularities, measure deviations. If the clearance is greater than 1.5 mm, replace the spring.

Thrust measurement is performed at the installed spring height. This determines how much pressure the spring creates when it is at its installed height on the cylinder head. This thrust is measured using a valve spring tester by compressing the spring to the installed height. The installed height for the tested spring is obtained from the information system or measured during disassembly. The tester measures the spring pressure when it is compressed. The deviation of the valve thrust force from the given value from the specification must not exceed 0.5 kg. When the value of the thrust force is not available, then compared with each other all the obtained values and assess their mutual deviation. The spring whose thrust is quite different from the average of all valves needs to be replaced.

To inspecting valve springs, follow these steps:

Height check

Use a movable gauge (caliper) to measure the spring’s free height and compare the measured values with the specifications for that motor. If the spring height is outside the specific value, replace the spring. Repeat this procedure for all other springs. When you do not have the necessary data, then compare all the measured sizes and estimate the deviation of the spring height.

Checking for squareness

Place the spring on a flat surface. Rotate the spring and check with a try square for any deviations. Measure these deviations. If the deviations exceed the limit value (1.5 mm), replace the spring.

Measuring thrust

Read or measure the installed spring height on the cylinder head. Install the valve spring to the valve spring tester. Pull the spring lever to compress the spring to the installed height. Note the thrust generated by the spring and compare it with the specifications. A spring that is out of specification needs to be replaced. When you do not have the required thrust force value, compare all the results obtained and estimate the average deviation.

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