What do I need to measure Babbitt (plain) bearing clearance?
18 Jul '17, 03:19
Apply one of below methods depending on design and size of Babbit bearing.
1) Feeler gauge
The easiest way to measure clearance in a plain bearing is to use feeler gauges. Match the thickest feeler gauge which can be inserted between the upper bearing shell and the shaft. However, some bearing and shaft arrangements do not allow to insert a feeler gauge. For example, in some engines, the crank shaft shape makes impossible to measure the clearance in the main bearing by feeler gauge. In such a case one of listed below methods may work.
2) Dial indicator.
The dial indicator magnetic base must be attached to bearing cap or equipment body and indicator needle must touch the shaft. To measure the clearance the shaft must be moved in 2 perpendicular directions: up-down & left-right - for horizontal shafts, fore-aft & left-right - for vertical shafts. Big diameter shafts could be jacked to achieve required movement inside the bearing. Be careful not to apply excessive force.
3) Lead wire or plastic gauge
This method requires bearing disassembling. For example, engine main bearing upper cap & shell could be lifeted and lead or plastic strip inserted between the shaft and bearing shell. The next step is to assemble the bearing and tighten it's bolts by recommended torque. After that upper bearing cap & shell to be loosen and lifted again to extract the strip and measure its thickness.
To use a micrometer shaft must be dismatled from the unit. After that it's diameter could be measured by ouside micrometer. Bearing must be assembled without the shaft and it's inner diameter could be measured by inside micrometer. The difference of above two measurements will give a clearance. Note that both shaft and bearing must be measured in two perpendicular dimension.
18 Jul '17, 03:47