Pistons and connecting rods (Peugeot 306)

Replacement of pistons and cylinder liners can only be performed with the power unit and gearbox removed. When purchasing new pistons and cylinder liners, be aware that they must be dimensionally matched and stored in pairs (on engines with wet cylinder liners). This also applies when reinstalling existing parts. In this case, it is necessary to apply the cylinder numbers to the working liners, pistons and connecting rods.

All pistons have two compression rings and one oil scraper ring. The upper compression ring has a chrome plated outer surface, and the second ring has a trapezoidal cross-section. Piston rings have markings that should be on top when installing the rings.

Although pistons and related components are not the same on all engines, this section provides a general description. If cylinder liners are not installed, the corresponding points are naturally skipped.

When ordering new pistons (and working cylinder liners) it is essential to indicate the engine number.

2.5.1. Disassembling pistons and connecting rods

To disassemble pistons and connecting rods, a special tool is required.

If this is not available, the work should be entrusted to a Peugeot service center. Also, if piston replacement is necessary, the same tool for pressing in piston pins is required. In addition, an electric stove is required to heat the connecting rod hole (but not the entire connecting rod) up to a temperature of 250°C. A fusible rod that softens at this temperature is also required for control. Having all these tools and experience, the work is carried out as follows:

• Remove the pistons and connecting rods from the working sleeves (or holes) cylinders. Check again that the markings are applied.

• Remove the piston rings from the pistons one by one using special pliers (Figure 120). If the rings are to be reinstalled, mark them. If you don't have special pliers, the rings can be removed by sliding metal strips under the ring from opposite sides of the piston. To avoid scratches, be sure to place one of the strips under the ring joint.
• For subsequent disassembly, a special tool is required. Place the piston on the fixture under the press, as shown in Figure 121, and press out the pin using the press punch. If the piston separates from the connecting rod, then this piston can no longer be installed, since the press-fitting place is damaged. In this case, it is necessary to replace the piston.

2.5.2. Checking pistons and connecting rods

• Check all details carefully. If parts show signs of metal corrosion, scratches or wear, they must be replaced.
• Measure the piston ring clearances by height in the piston grooves by successively inserting the rings into the corresponding groove on the piston (Figure 122). The gap is determined by a feeler gauge inserted into the gap between the ring surface and the piston groove surface. If the clearance dimensions do not correspond to the data given in the table of dimensions and adjustments, either the rings or the pistons are worn.

• After this, sequentially insert all piston rings from the top side into the working cylinder liner. Using an inverted piston, push the ring down to a distance of 15 mm from the bottom edge of the hole. To do this, place the cylinder block on its side. To measure the joint gap, insert a feeler gauge into the ring joint. Figure 123 shows how to correctly measure the piston ring joint gap. The joint clearances are not adjustable and if the joint clearances are increased, the piston rings must be replaced.
• Measure the piston diameter with a micrometer at a right angle to the piston pin along the lower edge of the piston jacket. Pistons are available in three size groups and the corresponding pins are color coded. Pistons and piston pins are supplied in pairs and are marked accordingly. It is not possible to describe all the differences between individual engines here. A letter is applied to the piston bottom, and the cylinder liner has markings in the form of one or more notches. There is also a colored spot indicating the piston pin fit. The piston pin has a marking of the same color.
• To check the piston clearance, measure the bore diameter. The holes are measured in the longitudinal and transverse directions and at three levels along the height of the working cylinder liner. In this way the maximum and minimum diameter are determined. Record the results.
• After this, subtract the piston diameter value from the hole diameter values. The difference is the piston clearance value. If the clearance value is outside the range of 0.06-0.08 mm, new sets of pistons and cylinder liners should be installed. Install pistons only with the same letter designations. It is quite possible that you will have to scratch off the carbon deposits in order to read the letter.
• Check the piston pins and piston bores for wear and damage. Pins are supplied complete with pistons only. The piston pin must have play in the piston hole, that is, when pressed by the finger, it must move in the piston.

2.5.3. Assembly of pistons and connecting rods

• It is assumed that all parts have been checked and repaired in accordance with section 2.5.2.
• Check the absence of twisting and bending of the connecting rods on a connecting rod testing machine. It is best to do this in a workshop, since bent or even twisted studs can interfere with the normal operation of the engine.
• Place the connecting rods on the hotplate. To do this, lay out the holes of the connecting rods on the tile in the shape of a star (Figure 125). Place something under the base of each crank to keep the cranks level. Continuously monitor the temperature with a fusible rod until it reaches 230°C. Connecting rod bearing caps should be screwed on so that a clearance of 1.0 mm remains between the connecting rod mounting surfaces and the connecting rod bearing cap.

• Place the piston pin on the mounting rod and screw the conical guide onto the other end, but do not tighten it. Generously lubricate the pin and rod with motor oil.
• When assembling pistons and connecting rods and using new bearing liners, connecting rods can be assembled with any piston. When reinstalling the old bearing shells, assembly is carried out in accordance with the markings made during disassembly. In any case, the arrows on the piston crowns must point towards the front of the engine. In addition, there is a "DT" marking, which indicates that this side should face the timing drive. The piston and connecting rod assembly is shown in Figure 126. These markings apply to all engine types.

• Place the piston on a special device and clamp it through the hole with a spring bar.
• Installation work must be carried out as quickly as possible to prevent the connecting rod from cooling down.
• Remove the connecting rod from the tile using a pipe wrench and insert it into the inside of the piston.
• Use your hand and a mounting rod to insert the piston pin (Figure 127). If necessary, rock the connecting rod to achieve a flush fit. Press the piston pin in until it stops. A special device ensures pressing in a precise position. After a few seconds, remove the cover from the piston and check the freedom of movement of the piston on the connecting rod after it has cooled.
• Unscrew the mounting rod from the piston and assemble the remaining pistons in a similar manner.
• Lubricate the support under the finger with oil from a grease can.
• Install the piston rings onto the piston in sequence. The marking of the two upper piston rings "Tor" must be located on top. Before installation, check each piston ring again, as it is easy to make a mistake when installing them. When installing piston rings, you will need piston ring pliers, but you can also place three metal strips around the piston (for example, probes) and put rings on the strips. Pull out the strips when the ring is pushed to the level of its corresponding groove. The rings break easily and must be installed with great care.
• Lubricate the piston rings thoroughly with engine oil and move them around the circumference, correctly positioning the ring joints.
• The joint of the oil scraper ring should be installed in the place shown in Figure 128, and the joints of the other two rings should be shifted from it along the circumference of the piston at angles of 120°.

• Lubricate the piston with engine oil and insert it into the corresponding cylinder bore. To compress the piston rings when installing the piston, appropriate compression bands are required. If there are working cylinder liners, apply a clamping band around the piston so that the upper edge of the piston still protrudes by approximately 4 - 5 mm (Figure 129). This ensures that the piston begins to move into the working cylinder liner. For a cast iron cylinder block, apply a tension band around the piston so that the lower part of the piston jacket remains free, as shown in Figure 130, and then push the piston into the hole from above in the manner shown in Figure 131. If there are working cylinder liners, insert the pistons so that the flat sides of the connecting rods and the surface of the upper side of the working liner are parallel and so that the arrow on the bottom of the piston points towards the front of the engine. The relative position of the connecting rod and the surface of the cylinder working liner is shown in Figure 132.
• If necessary, install new O-rings on the underside of the cylinder liners without displacing them around the circumference.
• Insert the working liners into the cylinder block after measuring their protrusions as described in section 2.3.
• After installing the working liners, check that the marks on the upper edges of the liners match the marks on the surface of the cylinder block and that all four arrows on the piston crowns point towards the timing drive.

Install the connecting rod bearing caps on TU type engines as described in section 2.3. On an XU type engine this is done as follows:

• First, tighten the nuts to a torque of 40 Nm. Then, loosen the nuts and tighten them again, this time to a torque of 20 Nm.
• From this position, tighten the nuts to an angle of 70°. Estimate the angle by eye or use a protractor.
• Check that the markings on the connecting rods and on the bearing caps on all connecting rods are on the same side.
• After tightening all connecting rod bearing caps, turn the crankshaft a few revolutions, checking for jamming.