Checking pistons and connecting rods (VW Sharan 1)

Clean the piston from carbon deposits and remove all deposits from the piston and connecting rod lubrication channels. Carefully inspect all parts. Cracks of any kind on the piston, piston rings, pin, connecting rod and its cover are not allowed. If they have scoring, scratches or signs of wear, these parts should be replaced. When inspecting the piston:

• measure the gap between the piston rings and the ring grooves in the piston head using a set of feeler gauges (Fig. 62). The nominal gap for the upper and lower compression rings 1 (Fig. 63) is 0.02 - 0.07 mm, and for the oil scraper ring 2 - 0.02 - 0.06 mm. The maximum permissible gaps for wear are 0.15 mm. If there is a gap, then either the ring or the piston ring groove is worn;

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• insert all piston rings one by one, starting with the lower one relative to the crankcase, into the cylinder bore. Turn one of the pistons over and push the rings down about 15 mm. After that, they will be directly in the cylinder bore;

• insert a feeler gauge into the piston ring groove — into the lock — to determine the gap (Fig. 64). For compression piston rings, the gap in the lock should be 0.2–0.40 mm, and for the oil scraper ring — 0.25–0.50 mm. The maximum permissible gap during wear for all rings is 1.0 mm;
• if the gap in the lock is too small (for example, new piston rings, which should also be measured), then it needs to be increased. The rings are very fragile, so this work should be done carefully. It is best to clamp the file in a vice and file down the end of the ring;
• check the piston pins and connecting rod bushings for wear and scoring. Even if only one connecting rod is damaged, the entire unit should be replaced;
• the connecting rod mounting bolts on the VR6 engine are screwed directly into the connecting rods (no nuts are used) and are so-called "flexible screws" that should be replaced after each unscrewing;
• check the connecting rods with a measuring device for twisting and bending.