All about Ford Mondeo

Piston rings - refitting
Engine removal and general engine overhaul procedures / Piston rings - refitting


1 Before installing new piston rings, check the end gaps. Lay out each piston set with a piston/connecting rod assembly, and keep them together as a matched set from now on.

2 Insert the top compression ring into the first cylinder, and square it up with the cylinder walls by pushing it in with the top of the piston (see illustration). The ring should be near the bottom of the cylinder, at the lower limit of ring travel.

16.2 When checking piston ring end gap, the ring must be square in the
16.2 When checking piston ring end gap, the ring must be square in the cylinder bore (this is done by pushing the ring down with the top of a piston, as shown)

3 To measure the end gap, slip feeler gauges between the ends of the ring, until a gauge equal to the gap width is found (see illustration). The feeler gauge should slide between the ring ends with a slight amount of drag. Compare the measurement to the value given in the Specifications Section of this Chapter; if the gap is larger or smaller than specified, double-check to make sure you have the correct rings before proceeding. If you are assessing the condition of used rings, have the cylinder bores checked and measured by a Ford dealer or similar engine reconditioning specialist, so that you can be sure of exactly which component is worn, and seek advice as to the best course of action to take.

16.3 With the ring square in the bore, measure the end gap with a feeler
16.3 With the ring square in the bore, measure the end gap with a feeler gauge

4 If the end gap is still too small, it must be opened up by careful filing of the ring ends using a fine file. If it is too large, this is not as serious, unless the specified limit is exceeded, in which case very careful checking is required of the dimensions of all components, as well as of the new parts.

5 Repeat the procedure for each ring that will be installed in the first cylinder, and for each ring in the remaining cylinders. Remember to keep rings, pistons and cylinders matched up.

6 Refit the piston rings as follows. Where the original rings are being refitted, use the marks or notes made on removal, to ensure that each ring is refitted to its original groove and the same way up. New rings generally have their top surfaces identified by markings (often an indication of size, such as УSTDФ, or the word УTOPФ) - the rings must be fitted with such markings uppermost (see illustration).

16.6 Look for etched markings (УSTDФ - indicating a standard-sized ring -
16.6 Look for etched markings (УSTDФ - indicating a standard-sized ring - shown here) identifying piston ring top surface

Note: Always follow the instructions printed on the ring package or box - different manufacturers may require different approaches. Do not mix up the top and second compression rings, as they usually have different cross-sections.

7 The oil control ring (lowest one on the piston) is usually installed first. It is composed of three separate elements. Slip the spacer/expander into the groove (see illustration).

16.7A Installing the spacer/expander in the oil control ring groove
16.7A Installing the spacer/expander in the oil control ring groove

If an anti-rotation tang is used, make sure it is inserted into the drilled hole in the ring groove. Next, install the lower side rail. DonТt use a piston ring installation tool on the oil ring side rails, as they may be damaged. Instead, place one end of the side rail into the groove between the spacer/expander and the ring land, hold it firmly in place, and slide a finger around the piston while pushing the rail into the groove (see illustration).

16.7B DO NOT use a piston ring installation tool when installing the oil ring
16.7B DO NOT use a piston ring installation tool when installing the oil ring side rails

Next, install the upper side rail in the same manner.

8 After the three oil ring components have been installed, check that both the upper and lower side rails can be turned smoothly in the ring groove.

9 The second compression (middle) ring is installed next, followed by the top compression ring - ensure their marks are uppermost, and be careful not to confuse them. DonТt expand either ring any more than necessary to slide it over the top of the piston.

10 With all the rings in position, space the ring gaps (including the elements of the oil control ring) uniformly around the piston at 120∞ intervals. Repeat the procedure for the remaining pistons and rings.


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