Checking the operating clearance of the connecting rod bearing
Note: At this stage, the crankshaft must be installed in the engine (see chapter 12).
1. As with main bearings, there must be a working clearance between the crankshaft journal and the bearing shells. There are two methods for checking clearance.
2. Place the cylinder block on a clean, level work surface, crankcase facing up. Turn the crankshaft so that the connecting rod journal of cylinder No. 1 is at BDC.
3. The first method is less accurate and consists in installing bearing caps on the connecting rods outside the crankshaft (inserts in working position) Measure the inside diameter of the assembled connecting rod end using a inside gauge. Then subtract from it the diameter of the corresponding connecting rod journal of the crankshaft, as a result, the operating clearance of the bearing will be obtained.
Note: Proper orientation of bearing caps is critical (see note in Chapter 7).
4. The second method involves using the Piastigage tool in the same way as when checking the main bearing running clearance (see chapter 12) and it is much more accurate than the previous method. Wipe all connecting rod journals of the crankshaft with a clean cloth. Place a piece of Piastigage thread on the bearing journal.
5. Install the upper bearing shell into the connecting rod, making sure that its mounting lug falls into the corresponding groove. Install the piston/connecting rod assembly to the crankshaft, then install the bearing cap using the manufacturer's marks.
6. Torque the bearing cap nuts/bolts to Step 1. Be careful not to dislodge the Plastigage or rotate the connecting rod.
7. Disassemble the assembly without moving the connecting rod. Use the scale printed on the Plastigage packaging to determine the operating clearance of the connecting rod bearing and compare the result with the data given in Specifications.
8. If the gap does not meet the regulated values, it is possible that the wrong size liners are installed (or they are excessively worn if the old bearings are installed). Make sure there is no dirt or oil between the bearings and the cap or connecting rod. Re-measure the diameter of the connecting rod journal of the crankshaft. Note that if one end of the Plastigage thread is wider than the other, the crankshaft journal may be tapered and needs to be reground.
9. When finished, carefully clean all traces of Plastigage from the crankshaft and bearing shells. Use a plastic or wooden scraper that won't scratch work surfaces.
Piston/Connecting Rod Assemblies - Final Installation
10. Note that the following procedure assumes that the crankshaft main bearing caps are already in position (see chapter 12).
11. Make sure the bearing shells are installed correctly (see the beginning of this Chapter). If new liners are installed, wash off all traces of protective grease with kerosene. Wipe the liners and connecting rods dry with a dense (lint-free) cloth.
12. Lubricate the cylinder walls, pistons, piston rings and upper bearing shells with clean engine oil (see illustrations). Arrange the piston/connecting rod assemblies in order on the workbench. Where bearing caps are secured with nuts, wrap the threaded ends of the studs with electrical tape to prevent scratching the connecting rod journals and cylinders when installing the pistons.
13. Begin by assembling piston/rod #1. Make sure the piston ring locks are still positioned as described in Chapter 13, then sink them into the grooves using a special compressor.
14. Insert the piston/connecting rod assembly into the top of #1 cylinder. Guide the bottom end of the connecting rod so that it does not damage the cylinder walls. Where oil jets are installed, be very careful not to break them when installing the connecting rods on the crankshaft journals.
15. Make sure the piston is correctly oriented in the cylinder - the piston head, connecting rods and connecting rod bearing caps have marks that should be directed towards the front end of the engine (see chapter 7).
16. With the hammer handle on the piston head, insert the assembly completely into the cylinder so that the piston head is flush with the top edge of the cylinder (see illustration).
17. Check that the bearing shell has not moved. Liberally lubricate the crankshaft journal and both bearing shells with clean engine oil. Being careful not to scratch the cylinder walls, slide the piston/connecting rod assembly onto the crankshaft crankpin. Remove from connecting rod studs (where there are) masking tape, oil the threads and the backs of the bolt heads. Install the connecting rod bearing cap, tightening the mounting nuts/bolts at this point by hand (see illustration). Note that the orientation of the bearing cap relative to the connecting rod is critical. The slots of both components, located close to their contact surfaces, must face the front end of the engine (i.e. in the direction of the arrow on the piston head) - see illustrations in Chapter 7.
18. On diesel engines, the piston heads are specially shaped to improve combustion characteristics. Pistons #1 and #2 are different from the rest of the pistons. On them, the large intake valve recesses should face the flywheel, and the large intake valve recesses on the other pistons should face the front end of the engine. New pistons have digital codes 1/2 on their heads (pistons #1 and #2), 3/4 (piston #3 or #4) and 3/4/5 (pistons #3, #4 and #5) (see illustration).
19. Tighten the mounting bolts/nuts with Stage 1 torque (see illustration).
20. Tighten the bolts/nuts to the angle specified in Step 2 (see illustration).
21. Install the remaining piston/rod assemblies in the same manner.
22. Turn the crankshaft by hand. Make sure it spins freely. Some rotational stiffness is quite normal if new components have been installed, but the shaft should turn smoothly without binding.
23. If new pistons are installed or a new «short motor» (see note in Chapter 5), measure the amount by which the piston heads at TDC protrude from the cylinder block to determine the required thickness of the gasket under the cylinder head.
24. Install the cylinder block crankcase down on the frame or wooden blocks. Attach a micrometer to the block and set its needle to zero when the probe of the device touches the surface of the block in contact with the cylinder head. Move the probe to the #1 piston head and slowly rotate the crankshaft to bring that piston to TDC. Record instrument readings (see illustration).
25. Repeat the measurement on the remaining pistons.
26. If the measurement results are different for different pistons, take the largest value to determine the type of gasket under the cylinder head - see specs.
27. Please note that if the previous pistons were installed, then the new cylinder head gasket must be identical to the old one.
28 See Section 1A, and install the oil pump and its suction pipe, sump and its baffle, flywheel and cylinder head.
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