Bearing clearance methods

Bearing Clearance Methods: 
It is important that regular checking of bearing clearance is carried out, as the clearance
determines the effectiveness of lubrication. 

Lead wire
 Traditional method, but requires that bearing are tightened just to obtain
clearance. Accurate as long as load is not over squeezed. Lead is not to squeeze blow 1/3rd of  original diameter. 

• Turn the crank shaft and set the crank at TDC position.  
•  Remove locking arrangements, mark the nut position. 
• Slacken the nut and lower the bottom half with bolts.  
• Then three lengths of lead wires would be laid circumferentially in the bottom half at three  places
• Place the bottom half into position and tighten the nut to its tightening torque.  
• Lower down the bottom half again.  
• Remove the lead wires and take the measurement.  
• It must have within the limit, if out of limit, the bearing shell must be replaced with new ones or  readjust the clearance by adjusting shims.   

Feeler gauge
Quick method, but more difficult to be accurate when using the long feelers 
as measuring point may not be the minimum point.

• Turn the crank shaft and set the crank at BDC.  
•  Insert the feeler gauge between lower half and crank pin.  
• Take the measurement readings. 

Plastigauge
Relies on the width of a plastic strip after compression. More accurate than
leads.

Bridge gauge
Depends on bedplate condition and crankshaft rigidity
Bridge gauge is an instrument for main bearing wears down measuring. 

• Remove the lube oil supply pipe.  
•  Remove upper bearing half and fit the bridge gauge.  
• Then take the measurement by inserting feeler gauge.

Micrometer
More accurate