Subaru 12033AB250 Piston Ring Set

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Lay out the pistons and new ring sets to match each ring set with the corresponding piston and cylinder during the side clearance check, end gap measurement, and engine assembly. Before installing the rings, check the piston ring side clearance by placing a new ring in each groove and using a feeler gauge beside it, ensuring to check at several points around the piston and using the correct ring for each groove, as they differ. A typical clearance for compression rings is around 0.0015 to 0.004 inch (0.038 mm to 0.101 mm), and if excessive, new pistons will be necessary. The ring end gaps must also be verified, assuming the side clearance has been confirmed. Insert the top ring into the first cylinder, squaring it with the cylinder walls using the piston, and position it near the bottom of the cylinder. To measure the end gap, use feeler gauges between the ring ends until the correct gauge slides in with slight drag; typical gaps range from 0.010 to 0.020 inch (0.25 to 0.50 mm) for compression rings and up to 0.030 inch (0.76 mm) for oil ring steel rails. If the gap is too small, carefully file the ring ends to avoid contact during operation, ensuring to file only by pushing the ring from the outside end of the file towards the vise. Excess end gap is not critical unless it exceeds 0.040 inch (1.01 mm), and it's important to double-check the ring type. Repeat this process for each ring in the first cylinder and the remaining cylinders, keeping rings, pistons, and cylinders matched. Once the end gaps are checked and corrected, install the rings on the pistons, starting with the oil control ring, which consists of three components: first, insert the spacer/expander into the groove, then install the upper side rail without using a piston ring installation tool to avoid damage, and finally, install the lower side rail, ensuring the upper rail spin stopper aligns with the side hole in the piston. After installing the oil ring components, verify that both side rails rotate smoothly in their grooves. Next, install the middle ring, ensuring the identification mark faces up, and use a piston ring installation tool for both the middle and top rings, being careful not to confuse them. Finally, repeat the procedure for the remaining pistons and rings.

Install the rings on the pistons, starting with the oil control ring, which consists of three components: spacer/expander, upper side rail, and lower side rail. Insert these components into the respective groove without the use of a piston ring installation tool. Verify that both upper and lower side rails can rotate smoothly. Proceed to install the number two (middle) ring, ensuring its identification mark faces upward, and the number one (top) ring in the same manner, with the mark facing up. Repeat these steps for the remaining pistons and rings, ensuring accurate installation for each.

Before installing the rings on the pistons, the piston ring side clearance must be checked by laying a new ring in each groove and slipping a feeler gauge in beside it. Check the clearance at three or four locations around each groove, ensuring to use the correct ring for each groove. A typical ring groove clearance for compression rings is around 0.0015 to 0.004-inch (0.038 mm to 0.101 mm). If the side clearance is excessive, new pistons will have to be used.

To prepare the pistons and new ring sets for engine assembly, ensure they are matched for subsequent side clearance check and end gap measurement.

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