B20, B21, B23, B30, B230 and B234 Engines
See Figures 1 and 2
This procedure is more easily accomplished with the engine removed from the vehicle and placed on an engine stand.
- Remove the cylinder head. Remove any ridge and/or carbon deposits from the upper end of the cylinder bores with a ridge reamer.
- Remove the oil pan. Check connecting rods and pistons for identification numbers and, if necessary, number them.
- Remove the connecting rod nuts and caps from the crankshaft. Push the rods away from the crankshaft and install the bearing shells, caps, and nuts on the rods to avoid possible interchange of parts.
- Push the piston and rod assemblies up and out of the cylinders. Remove the rings. Use care not to let the ends of the rods bang against the cylinder walls.
See Figure 3
Pistons and cylinder liners are sold as a unit.
- Remove the engine from the vehicle and remove the cylinder heads. Be sure to hold the liners in place with retainer straps.
- Remove the 23 bolts holding the front oil pan and remove the oil pan and gasket.
- Remove the three bolts holding the oil strainer. Remove the rubber ring from the suction pipe.
- Remove the front baffle plate.
- Remove the eight main bearing nuts and all of the lower crankcase bolts and remove the lower crankcase. Remove the rubber ring for the oil channel.
- Install spacers on the main bearing studs and install the main bearing nuts to hold the main bearing caps in position.
- Check the markings on the connecting rods and caps; make sure they agree with the markings in the illustration. If not, mark each rod and cap yourself.
- Remove the nuts and bearing caps and press the connecting rods and pistons out of the cylinders.
The best method for engine rebuilding is with the engine removed from the vehicle.
- Remove the cylinder head and the oil pan.
- Number the pistons for identification. Number the connecting rods and their caps for identification.
- Remove the connecting rod nuts, remove the caps, and push the pistons with connecting rods out of the top of the block.
See Figures 4, 5, 6, 7 and 8
- Inspect the cylinder walls for scoring, roughness, or ridges formed by excessive wear. With an accurate cylinder gauge or inside micrometer, check for cylinder taper and out-of-round at the top, middle, and bottom of the bore.
- Check in directions parallel and at right angles to the center line of the engine. Wear is indicated by the difference between the highest and lowest readings. The cylinder is in need of reboring when wear reaches 0.010 in. (0.25mm), or if scoring is evident.
- Use a hone or rebore the cylinder for fitting of smallest possible oversized piston and rings. Clearance between the piston and cylinder wall, with the rings removed, should be 0.0008-0.0016 in. (0.02-0.04mm) for the B20 and B30 engines and 0.0004-0.0012 in. (0.01-0.03mm) for the B21/B23/B230/B234 engines. For the B27 engine equipped with Demolin pistons, clearance should be 0.00315-0.00394 in. (0.08-0.10mm). On the B27/B28/B280 engine equipped with Mahle pistons, clearance should be 0.0008-0.0016 in. (0.02-0.04mm).
- Check the piston ring end-gap by pressing each ring into the cylinder bore and squaring it in the bore with the piston. Insert a feeler gauge into the gap. Check the gap against the specifications given earlier in this section. The gap may be widened by filing the ring ends with a thin flat file.
- Clean the ring grooves on the sides of the pistons. With the rings installed in their respective grooves, measure the side clearance at several points around the piston, and check the reading against the specifications. Inspect the ring grooves for wear, especially the upper edge of the chromed top compression ring.
- The wrist pins on the B20, B30, and B21/B23/B230/B234 engines are removed after the circlips are taken out of the wrist pin bores. The wrist pins should slide out.
- The wrist pins on the B27/B28/B280 engine and the diesel must be pressed out using a hydraulic press. On the B27/B28/B280 engine, press the wrist pin in and out in the direction opposite to the arrow on the piston. (When installing, heat the connecting rod to 480°F (249°C).
- On the B27/B28/B280, once the wrist pin is removed the piston cannot be reused because of deformation. On the diesel engine, remove the circlips, then press out the pin. If the pin is tight, heat the piston to 140°F (60°C).
- Check the connecting rods for straightness, and check the bushings for excessive wear. The wrist pin should slide through the bushing with light thumb pressure, but without noticeable looseness.
See Figures 9 through 14
On all engines, the notch or arrow stamped on top of the piston must face the front of the engine. On B20 and B30 engines, the connecting rod crank end marking must face away from the camshaft side. On the B21/B23/B230/B234, the connecting rod marking must face the front of the engine.
On the B27/B28/B280, the shoulder on the crankshaft end of the connecting rod must point toward the front of the engine for connecting rods marked B, D, or F (for cylinders 4, 5 and 6). The shoulder on the crankshaft end of the connecting rod must face toward the rear end of the engine for connecting rods marked A, C, or E (for cylinder 1, 2 and 3).
For diesel engines, the cast marks on the connecting rod and cap must face toward the oil filter side of the engine.