XU series engine
1. On early engine models, new liners must be installed during a major overhaul. On later engine models, the running clearance check can be performed using the original liners. However, a new set is preferable, as the results obtained will be more accurate.
2. Clean the rear of the bearing shell and its installation location in the cylinder block and main bearing caps.
3. Install the bearing shells in their places. Note that the upper bearing shells have a grooved working surface, while the lower shell has a solid working surface.
4. The working clearance can be checked using two methods.
5. One of the methods (which requires the presence of a micrometer to measure the diameter of the holes) consists of installing the main bearing caps together with the shell on the cylinder block and screwing them down to the required torque. Measure the inside diameter of each assembled pair of bearing shells. Measure the diameter of each crankshaft main journal. Subtract the corresponding crankshaft main journal diameter from the measured bearing diameter.
6. Second (and more accurate) the method is to use a product known as Plastigage. This is a round plastic rod that is compressed between the bearing shell and the crankshaft journal. After removing the main bearing cap, the deformed plastic rod is measured with a special template that is included with the Plastigage. The procedure for using Plastigage is as follows.
7. Install the crankshaft without lubrication on the liners installed in the engine block. The crankshaft journals and liners must be completely clean and dry.
8. Cut a few pieces of Plastigage plastic rod (they should be slightly shorter than the width of the main bearings) and install them on each crankshaft journal.
9. Install the caps with the lower liners and tighten the mounting bolts to the specified torque. Do not rotate the crankshaft during the Plastigage clearance measurement.
10. Unscrew the liner mounting cover, remove it and apply the scale ruler printed on the package to the deformed plastic rod. By comparing the width of the deformed plastic rod with the control width on the scale ruler, determine the size of the gap.
11. Finally, thoroughly clean any traces of Plastigage material from the bearings and crankshaft.