Engine Maintenance Focus, Auto Repair Master's Explanation

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The engine assembly sequence varies depending on the engine structure, but the basic order remains the same.

For an overhead cam engine, the assembly sequence is as follows:

Crankshaft-flywheel Assembly Installation

1. Install the flywheel onto the rear flange of the crankshaft. Position it with two locating bolts before tightening the nuts. Tighten the nuts diagonally, applying a torque of 137-147 N·m.

2. Install and secure the main bearings in the crankshaft main bearing housing (align the bearing oil holes with the bearing oil gallery holes). Lightly apply engine oil to the bearing shells.

3. Install the crankshaft into the main bearing housing. Install the main bearings without oil grooves into the main bearing caps. Position each main bearing cap on each main journal and tighten the main bearing bolts sequentially to the specified torque. Tighten the bolts in two to three passes, working from the center outwards in a crosswise pattern. Tighten to a torque of 170-190 N·m. After tightening, the crankshaft should rotate with a torque no greater than 30 N·m. If not, install a gasket between the main bearing seat and the main bearing cap.

4. Install the crankshaft timing gear, oil deflector, torsional vibration damper assembly, starter pawl, etc. on the front end of the crankshaft in sequence.

Piston and Connecting Rod Assembly Installation

1. Lightly oil the piston pin and the small end of the connecting rod. Heat the piston in over 90% hot water, then remove the piston. Quickly insert the piston pin into the piston pin seat and the small end of the connecting rod to connect the piston and connecting rod. Use needle-nose pliers to install the piston pin locking ring in the ring groove at each end of the pin seat. (During installation, ensure that the notch on the top edge of the piston faces the same side as the protrusions on the connecting rod body and connecting rod cap, i.e., the front of the engine.) 2. Use piston ring pliers to install the air ring and oil ring in sequence. Be careful not to install the twisted ring upside down (internal twisted rings are generally installed in the first ring groove with the edge notch facing upward; external twisted rings are generally installed in the second and third ring grooves with the edge notch facing downward).

3. Stagger the end gaps of each ring groove at a certain angle (the three air rings are staggered 120°, and the end gap of the first ring should avoid the piston pin seat and the side with greater side pressure). Tighten the piston rings with the piston ring clamp. Gently tap the top of the piston with the wooden handle of a hammer to allow the piston to enter the cylinder until the connecting rod big end connects with the crankshaft connecting rod journal. Install the connecting rod cap and tighten the connecting rod bolts and nuts to the specified torque of 80-100 N·m.

4. Before installing the piston and connecting rod assembly into the engine, check its perpendicularity to ensure it meets the requirements. Lubricate the piston, piston rings, and the inner surface of the cylinder liner. Then, use the piston ring clamp to install the piston and connecting rod assembly into the cylinder liner, as shown in Figure 8-1.