Method for measuring the radial clearance between the piston compressor main shaft bearing shells (thin-walled bearings) and the main shaft journal

The radial clearance between the main bearing shells and the crank journal is usually measured using plastic gauges (such as wire). Place the wire between the bearing and the crank journal, then tighten the bearing cover; the gap size is obtained by compressing the wire. Your measurement method seems to calculate the average of the compression values of the three wires, whereas the manufacturer’s method uses the compression value of a single wire directly. The correct method of measurement should be: 1. Place the wire at several different positions on the crank journal. 2. Tighten the bearing cover to flatten the wire. 3. Remove the bearing cover and measure the thickness of the flattened wire. 4. Determine the actual clearance between the bearing shell and the crank journal by measuring values. If your method involves using three wires at the same location to calculate an average, this may lead to errors. Wires should be placed at different positions on the bearing shells (for example, in a 120-degree distribution), and the thickness of the wires after being compressed should be measured; the minimum value among these measurements shall be used as the radial clearance value. This can more accurately reflect the actual condition of the bearing. In summary, your measurement method may have resulted in a value of 0 mm due to errors in the measurement steps or understanding; this is impossible, as any bearing should have some degree of operating clearance. It is a common practice to determine the gap directly using the compression value of a single wire according to the manufacturer’s method. Therefore, the manufacturer’s measurement methods should be referred to in order to determine whether the gap meets the maintenance standards. .

Your measurement method is correct, but nowadays, at positions B and C, wire is not used; instead, white steel sheets are employed, with an area equal to that of the surface in contact with the bearing shell. Wire can easily cause deviations. There is an error in your calculations: the bearing shell clearance should be equal to wire A plus (wire B + wire C)/2. Based on your measurement values, the clearance should be 0.14

The principle is fine, but to achieve accurate measurements, pay attention to the details. 1. For thin-walled tiles, copper sheet is usually placed at the tile joint, and lead wire is placed at the top; the lead wire should be placed horizontally, using two wires, as shown in the attached diagram. Note that, generally, based on the shaft diameter, we can estimate the range for the bearing clearance. For example, for a shaft with a diameter of 300, the bearing clearance is usually between 0.4–0.5 mm; therefore, when using lead wire, one should use wire with a diameter greater than 0.5 mm – 0.7 mm is recommended. A copper sheet with a thickness of 0.1 mm should be used for the bearing surfaces, so that the measurement using the lead compression method yields more accurate results. 2. Looking at the pictures ABC from the original poster, why is A placed on top of the lower tile? In fact, to check the bearing shells (main shaft bearings) of reciprocating machines, it’s sufficient to use a micrometer and an inner diameter gauge; there’s no need to use lead wires, as lifting the crankshaft back and forth is rather troublesome. We usually first take a measurement to determine the contact area; at the same time, we use the lead compression method to measure the clearance of the bearing shells, while a feeler gauge is sufficient for measuring the lateral clearance.

That’s right; sensible people know that for thin-walled bearings, especially in reciprocating compressors, this applies whether it’s the seat bearings, the large-end bearings, or the small-end bearings. It is recommended to use a micrometer to measure the shaft diameter, and an inside diameter gauge to measure the hole diameter; then compare the two values. The same is true for back tension

This post was last edited by we11we11 on 2024-2-27 at 07:33. Thank you; your explanation is very detailed. Also, based on the orientation of the image, should the wire be placed vertically (along the axis), while if it’s horizontal, it would be perpendicular to the axis? Should the measured gap value be reduced by the thickness of the copper sheet (0.1mm) to obtain the actual gap value?

I’m not quite sure why it’s the addition of values

Yes, yes, it’s in the forward direction; I wrote it wrong

The lead wires placed at positions B and C increase the gap between the bearing shell and the shaft diameter; therefore, the value for A must decrease. The amount by which it decreases is equal to the average of B and C. The reason for taking an average of B and C is that the pressures on both sides may differ, resulting in different values for B and C. Taking an average helps to reduce errors. Thus, the average gap referred to here is the average of multiple measurements, that is, the average of the values obtained by calculating A + (B+C)/2 multiple times

This post was last edited by we11we11 on 2024-2-28 at 11:13. I just don’t quite understand it: it is precisely because the wires placed at positions B and C increase the gap between the bearing shell and the shaft diameter, that the actually measured gap value A is larger than the true gap. Therefore, the true gap should be calculated by subtracting the average of B and C from the measured value A. So it seems to me that the formula for the main shaft bearing gap, namely A – (B+C)/2, is correct