All engines
1. Previously, the connecting rod and piston assemblies must be thoroughly cleaned. Piston rings must be removed.
Piston rings must be replaced without fail.
2. Using a special tool or several blade-type probes, remove the rings from the pistons - try not to accidentally damage the walls of the latter.
Removing piston rings with a blade-type feeler gauge (it is better to use two or three probes at the same time)
Remember that the rings are made of brittle metal and can break if pressed hard - do not injure yourself!
3. Scrape off any carbon deposits from the piston crowns. After removing the main layer of deposits, sand the surface by hand with a wire brush or a piece of fine sandpaper.
Under no circumstances should wire attachments for an electric drill be used to clean pistons made of soft material and easily eroded! After stripping, the markings applied to the piston bottoms must be clearly distinguishable.
4. Using a special tool, clean the grooves for the installation of rings on the pistons. Alternatively, you can use a piece of an old piston ring for this purpose, but be careful not to scratch the bottom and walls of the groove and do not cut your fingers.
Cleaning grooves for installing piston rings with a special tool
5. After removing the main deposits, wash the connecting rod assemblies with a solvent and dry them thoroughly, if possible using compressed air. Check the patency of the oil return holes in the rear walls of the grooves for the installation of piston rings, as well as the oil holes in the lower heads of the connecting rods.
Remember to wear protective goggles when using compressed air!
6. If the piston walls and cylinder bores are not damaged or excessively worn, and the engine block has not been machined or replaced, there is no need to replace the pistons either. Normal wear of the pistons is manifested in the form of vertical wear marks along the thrust surface and a slight slack in the fit of the upper compression ring in its groove. Do not forget that the replacement of piston rings is mandatory, regardless of their condition.
7. Carefully inspect each of the pistons for cracks in the skirt, around the protrusions for the installation of piston pins and in the area of \u200b\u200bthe rings.
8. Check the thrust surfaces of the piston skirt for scratches, the bottom for through holes and burnouts along the edge. The presence of scratches on the skirt can be regarded as a sign of prolonged overheating of the engine, or too early ignition of the air-fuel mixture - check the correct functioning of the cooling system. Burnouts along the edges of the bottom are evidence of detonation. In any case, the cause of the identified violation must be eliminated in order to avoid relapses. Intake air leaks, incorrect air-fuel mixture layout, incorrect ignition timing, incorrect functioning of ignition and EGR systems can also be possible reasons for the formation of the listed defects.
9. Pitting of pistons in the form of cavities indicates that coolant has entered the combustion chambers and / or crankcase of the engine. Again, make sure that the cause of the internal leaks is corrected.
10. Assess the backlash of the piston rings in their grooves by inserting a new ring from the outside into your groove on the piston and using a blade-type feeler gauge to measure the remaining gap. Repeat the measurement at two to three points along the perimeter of the groove. Be careful not to mix up the compression rings - the top one is different from the second one. If the gap exceeds the allowable value (see Specifications in Chapter Engines), pistons must be replaced.
Checking the clearance of the piston ring in the groove
11. Determine the size of the piston clearance in your cylinders, for which measure the diameters of the latter (see Section Cleaning and checking the condition of the cylinder block) and subtract from them the diameters of the corresponding pistons. The piston diameter is measured along the thrust surface of the skirt at an angle of 90 degrees. to the axis of the piston pin and at a given distance from the bottom. If the piston clearance in the cylinder exceeds the allowable value (see Specifications in Chapter Engines), the block should be given to the groove with a selection of new pistons and piston rings of a repair diameter.
The piston diameter is measured in a plane perpendicular to the axis of the piston pin..
12. Assess the correct fit of the pistons on the connecting rods by trying to rotate the components in opposite directions. The presence of any noticeable play indicates excessive wear on the joint. To correct the situation, the connecting rod and piston assemblies should be delivered to a car service workshop, where the necessary refurbishment and replacement of fingers will be carried out.
Gasoline engines
On all gasoline engines, the piston pins are press fit in the upper heads of the connecting rods and have a floating fit in the piston bosses, which is why the procedure for removing the pistons from the connecting rods (in case such a need arises) should also be entrusted to car service specialists. In parallel, connecting rods can be checked for signs of bending, twisting and other deformations using special diagnostic equipment.
Unless necessary, pistons should not be removed from the connecting rods.
Diesel engines
1. On diesel engines, the pins also float in the connecting rods and are secured to the pistons with circlips. If necessary, using a suitable screwdriver, remove the circlips and manually press the pin out of the assembly. Mark the removed finger with adhesive tape to belong to your connecting rod and piston assembly and put it in a safe place. Retaining rings during assembly must be replaced without fail.
Removing the piston pin circlip
2. Examine the upper head of the connecting rod and the piston pin for signs of wear and scoring of other mechanical damage. Measure the diameter of the finger with a micrometer, compare the measurement result with the requirements of the Specifications in the Chapter Engines, replace if necessary. If the pin or connecting rod is worn out, both parts must be replaced.
3. The connecting rods themselves (in the absence of mechanical damage) do not need to be replaced - visually assess for signs of obvious deformations, if there are suspicions of bending / twisting, contact a car service specialist for help, or replace defective components.
4. After evaluating the condition of all components, prepare replacement parts. Replacement pistons come to the aftermarket complete with pins and circlips.
Retaining rings can be purchased separately.
5. Assemble the pistons with the connecting rods in such a way that the protrusion on the connecting rod on the bearing side is on the flywheel side, the arrow on the piston bottom should point in the direction of the engine timing belt
The connecting rod is mounted on the engine with a ledge (A) towards the flywheel/drive plate, while the arrow stamped on the piston crown must point in the opposite direction (towards the timing drive)
6. Lightly lubricate the piston pins with clean engine oil, and use them to secure the pistons to the upper heads of the connecting rods. Be convinced of freedom of rotation of the piston concerning a rod on an axis of a finger. Install new circlips (locks up) and make sure they fit securely in the receiving grooves.
All engines
1. Check the connecting rods for cracks and other mechanical damage. Temporarily remove the lower head covers, remove the old bearing shells, wipe the beds in the covers and heads and check them for burrs, scuffs and roughness. When finished checking, put the liners in place, install the caps on the lower connecting rod heads, and finger-tighten the mounting bolts.
If the engine is being repaired to eliminate finger knocking, replace the connecting rod assemblies.
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