- Clean the grooves for the rings and rings from carbon deposits.
- Measure a backlash between piston rings and grooves under rings as it is shown in fig. 73. If the gap measured with a feeler gauge exceeds 0.15 mm, then the ring or piston is considered worn. The normal gap is 0.02-0.05 mm.
Take a set of new piston rings and repeat the groove clearance measurement. If the gap exceeds 0.05 mm, then replace the pistons. If the gap does not exceed 0.02-0.05 mm, then use new rings. In addition to this gap, it is necessary to measure the gap in the piston ring lock as described below:
- Insert all rings one by one into the cylinders from the crankcase side and advance 15 mm deep with the piston head. This will ensure that the ring is correctly installed.
- Insert a probe into the gap between the ends of the ring, thus determining the gap in the lock (pic. 74). For compression rings, the gap in the lock should be 0.3–0.5 mm, and for oil scraper rings, 0.25–0.4 mm. The maximum allowable gap in the lock is 1 mm for all rings.
- If the gap is too small (this happens in new rings, which must be checked), then you can increase it by sawing both ends with a needle file, holding the ring in a vise, as shown in fig. 75. If the gap is large, this ring must be replaced.
Check the degree of wear of the piston pin and the bushing of the connecting rod head.
The maximum allowable clearance between the pin and the sleeve is 0.1 mm. If the clearance is greater, replace the pin. If this does not help, then it is necessary to drill the bushing from the upper head of the connecting rod, press in a new one and turn it to fit the size of the piston pin.
Check the connecting rods for deformations on a special stand.
If at least one connecting rod requires replacement, then replace the entire set.
The connecting rod bolts and nuts should always be replaced. Procedure for measuring clearance in connecting rod bearings described here.
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