Mounting diagram of the piston and connecting rod
1 piston ring
2 Piston pin circlip
3 Piston pin
4 piston
5 Connecting rod
6 Connecting rod bolt
7 Cylinder block
8 Connecting rod bearing shell
9 Connecting rod bearing cap.
10 Connecting rod bearing cap nut
11 Oil jet
12 Pressure relief valve, opens at 2.5-3.2 bar. The letters indicate the designations of the connecting rod and cover (A) and location of cast protrusions (IN). The latter should face the pulley
Pistons and connecting rods are knocked out from the inside of the cylinder block upwards with a hammer handle after removing the connecting rod bearing caps and bearing shells. When carrying out this work, the following instructions should be observed regarding the designations and installation positions of parts, as well as the features of various engines. The instructions apply to all engine types.
Withdrawal
Each piston and related connecting rod should be marked with the number of the cylinder from which it was removed. It is best to apply this number with paint on the bottom of the cylinder. In addition, on the bottom of the cylinder, you need to draw an arrow pointing to the front side of the engine.
When removing pistons with connecting rods, mark the exact installation position of the connecting rod bearing caps and immediately after removing the connecting rod and bearing cap, apply the cylinder number on one side. This is best done with a punch (for cylinder No. 1 - one blow with a center punch, etc.).
The connecting rod and connecting rod bearing cap must be assembled so that the cast lugs are against each other. Both cast protrusions after installing the connecting rod must face the crankshaft pulley.
Some gasoline and diesel engines have oil jets to cool the pistons. They are located at the bottom of the cylinder bores.
Mark the position of the bearing shells according to the numbers of the connecting rods and their position relative to the bearing caps. Also mark the top and bottom liners with paint on the back.
When ordering new pistons, be sure to specify the model and year of manufacture. The pistons are manufactured to match the compression ratio and have different recess depths.
When removing the pistons and disconnecting them from the connecting rods, proceed as follows:
Remove the bearing caps and bushings by knocking out the parts as indicated. If necessary, scrape off the oil carbon ring at the top of the cylinder bore with a scraper.
Press out the piston pin after removing the circlip. A cutout in the piston pin hole allows the use of a pointed tool for removal. so that you can pry off the retaining ring, as shown in the figure. The finger should be pressed out with a suitable punch (mandrels).
Remove the piston rings in order using a piston ring plier. If the rings are to be reinstalled, they must be marked accordingly. Piston rings are very fragile, which means that when removing them, even with a puller, you have to be very careful not to open them too much.
If a piston ring remover is not available, metal strips can be pushed under the ring evenly, in different places of the piston. One strip must always be under the lock of the ring to avoid scratches.
After removing the piston ring, it should be inspected immediately. Both upper rings are marked on one side with the word "TOR" or word "OBEN". This side after installing the ring should be on top. The third ring can be installed on either side.
Measuring cylinder bores
To measure the cylinder bores, you need to use a special dial gauge, with which you can measure the top, middle and bottom of the hole. If the dial gauge is not available, this operation cannot be performed.
The cylinder bore should be measured in the directions "A" And "IN". In addition, measurements should be made at a distance of 10 mm from the top edge, 10 mm from the bottom edge and in the middle part, i.e. at levels 1, 2, and 3. In total, six measurements must be made for each cylinder bore. All measured values must be recorded and compared with those given in the tables of dimensions and adjustment parameters.
It should be borne in mind that you will have to bore all the cylinders, even if the dimensions of one of the cylinders are not normal. A deviation of 0.08 mm from the nominal value is permissible. Piston repair dimensions are indicated in the tables of dimensions and adjustment parameters.
The final size of the cylinder bore is determined by measuring the piston diameter, which is taken 10 mm from the bottom edge of the piston skirt and at the right corner of the piston pin bore.
To this dimension, add the piston clearance of 0.03 mm. In addition, an addition of 0.02 mm for cylinder honing should be taken into account. To check the piston clearance in the cylinder bore, measure the piston and cylinder bore as described above and calculate the difference between these values. If the result exceeds 0.08 mm, it is necessary to bore the cylinders, since the gap has reached the wear limit.
Checking pistons and connecting rods
All details should be carefully checked. If parts show signs of gouging, gouging or wear, they must be replaced. The following piston checks should be made:
Measure the piston ring gaps in the grooves in height by installing the rings one by one in the corresponding grooves. The clearance between the ring surface and the piston groove surface is determined using a flat feeler gauge. If the ring gap exceeds 0.12 mm, either the rings or the pistons are worn. The nominal value is 0.02-0.07 mm.
Insert all piston rings in order from the underside of the cylinder block into the cylinder bores. Using an inverted piston, the rings should be pressed down by about 15 mm. In this case, both ring taps should be moved to measure the gap in the ring lock.
Nominal values are indicated in the tables of dimensions and adjustment parameters. The wear limit is different for different piston rings.
With too little clearance (for example, if the ring is new), the edges of the ring should be ground off. To do this, clamp the file in a vise. If the gap in the ring lock is too large, the corresponding ring must be replaced.
Piston pins and connecting rod bushings should be checked for wear and wear. If at least one connecting rod is unusable, the entire set should be replaced.
The connecting rod bearing nuts must be replaced every time.
Connecting rods should be checked for bending and twisting in a special tool.
Check connecting rod bolts for damage and replace if necessary. In this case, expansion bolts are used and they should only be replaced with the same ones.
Assembly of pistons and connecting rods
If the jet was removed to cool the piston, it should be screwed together with the safety valve (27 Nm). The jets are located at the bottom of the cylinder bores.
If pistons are replaced, check that all pistons are of the same type.
Heat pistons to 60°C (put in hot water). Care should be taken to have a suitable tool that can be applied to the inside of the piston pin.
Press your fingers into the heated pistons and into the connecting rods.
When assembling pistons and connecting rods, follow these instructions:
Arrow on the bottom of the piston (or painted or embossed on a new piston) must face the front of the engine.
The cast lugs on the connecting rod and bearing cap must face the pulley. The cylinder number designations on the connecting rods and bearing caps must match.
Check that, after reassembly, the piston can swing freely on the connecting rod when moved in the direction of the arrow.
Using piston ring pliers, install the rings one by one into the grooves. Both compression rings can be mixed up, and therefore it is necessary to check their cross-section before installation. In addition, both compression rings are marked on one side with the word "TOR" or "OWEN" and this designation after installing the ring should be read from above.
Install the oil scraper ring, consisting of three parts, evenly distributing the locks
Installation, pistons and connecting rods
Lubricate the cylinder bores well.
Arrange all connecting rods according to cylinder numbers. The cast lugs on the connecting rods and bearing caps must face the crankshaft pulley.
The arrows on the bottoms of the pistons should point towards the front of the engine.
Arrange the piston ring locks at the same distance around the piston circumference i.e. through 120°. The piston and connecting rod wiring diagram shows how the locks should be located in relation to the piston pin.
Position the clamping band for the piston rings. as shown in the figure and press the piston rings into the grooves. Check that they are well pressed.
Slide short lengths of rubber or plastic tubing over the connecting rod studs to avoid scratching the cylinder bore.
Rotate the crankshaft until the two journals are at bottom dead center.
Push the connecting rod into the hole from above. For this, the engine must be laid on its side so that you can bring the connecting rods to the bearing journals and not scratch the cylinder bores or the connecting rod journals. The connecting rod bearing shell must already be in the connecting rod, with the protrusion in the recess.
Push the piston in until the rings slide one by one into the cylinder bore and the connecting rod base sits on the crankshaft journal. Be careful not to scratch the bearing neck.
Place the second bearing shell into the bearing cap, grease the shell well, press the cap onto the connecting rod studs and tap lightly. Pieces of rubber tubes must first be removed. Be sure to pay attention to the fact that the cast protrusions on the connecting rod and the connecting rod bearing cap match, otherwise you can make a mistake at the last moment
Lubricate the contact surfaces of the nuts on the connecting rod bearing caps with oil. Tighten the connecting rod bearing cap nuts alternately to 30 Nm and from this position tighten by another 90°, i.e. a quarter turn.
After screwing the connecting rod bearings, each bearing should be inspected again. It is known from experience that defects in connecting rod bearings sometimes appear after repairs are completed, when the bearing cap and connecting rod are not screwed perfectly. Numeric (1) the figure indicates both of the above-mentioned cast protrusions, and the number (2) - designations of the connecting rod bearing cap and connecting rod, in this case for the second cylinder. The specified labels should be located on all connecting rods opposite each other. This check must be carried out before closing the engine crankcase.
After installing the connecting rods, the crankshaft must be rotated several times to determine if there are any jams. If there is, you need to check again if the pistons are in the correct position, i.e. the arrows on the bottoms should point forward (pulley side).
Use a feeler gauge to check the clearance between the side surface of the connecting rod and the surface of the crankshaft.
In this case, push the connecting rod bearing to the right, as shown in the figure, so that there is a gap for pushing in the measuring probe. This is the axial clearance of the connecting rod bearing and should not exceed 0.37 mm.
Install oil pan.
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