Elements of the piston group
Correct positioning of the piston relative to the connecting rod on diesel engines
Examination
1. Before checking the pistons with connecting rods, remove the piston rings from the pistons and thoroughly clean the pistons.
2. To remove piston rings from pistons, spread the ring apart and insert two or three old feeler gauge blades evenly around the circumference of the ring and slide the ring off the piston using them. Be careful not to scratch the piston with the ends of the ring. Rings are very fragile and can crack if spread too much. The working edges of the rings are very sharp, so handle them carefully to avoid cutting yourself.
3. Keep each set of rings with the piston for reinstallation.
4. Clean all traces of carbon from the top of the piston.
5. Remove carbon deposits from the piston ring grooves using an old ring.
6. After removing the deposits, clean the piston and connecting rod with a suitable solvent and wipe them dry.
7. When assembling the engine, it is advisable to use new piston rings.
8. Carefully inspect each piston for cracks around the skirt and piston pin holes.
9. Check for wear on the piston skirt, piston head bore, and burn marks on the top of the piston.
10. Traces of pitting corrosion on the piston indicate that coolant has entered the combustion chamber. It is necessary to find the cause of the liquid entering the combustion chamber and eliminate it.
11. On engines with aluminum cylinder blocks with wet liners, pistons cannot be replaced separately; pistons are supplied complete with rings and sleeves.
12. Check each connecting rod for wear, cracks, and distortion.
13. It is recommended to replace the studs and nuts securing the lower connecting rod head during each disassembly.
14. On all petrol engines the piston pins are pressed into the upper head of the connecting rod, so connecting rod replacement must be carried out in a specialized workshop.
15. On diesel engines, the piston pins are installed with a sliding fit and are fixed in the piston by two retaining rings. On these engines, the pistons and connecting rods can be separated as follows.
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16. Using a thin screwdriver blade, remove the retaining ring from the piston and push out the piston pin by hand. When reinstalling the piston pin, use only new retaining rings.
17. Check the piston pin and big end bearing for wear.
18. Connecting rods usually do not require replacement unless the engine has seized up beforehand.
19. Install the piston on the small end of the connecting rod so that the arrow on the piston crown is on the side of the small end marking. Lubricate the piston pin and insert it into the piston and small end of the connecting rod. Check that the piston rotates easily and freely on the piston pin, then secure the piston pin with new circlips. Check that each circlip is correctly positioned in the piston groove (see figure Correct piston position relative to connecting rod on diesel engines).