23.13 Measuring the piston diameter at the specified distance from the bottom of the skirt

23.14a Rock the piston pin back and forth to check for freeplay

23.14b Measuring the pin bore in the piston

Engine, clutch and transmission 2*41

24.3 Measuring installed ring end gap

specified, renew the components that are worn beyond their specified limits. Check the measurements between the pin and the connecting rod small-end (see Section 22).

Installation

15. Inspect and install the piston rings (see Section 24).

16. Lubricate the piston pin, the piston pin bore and the connecting rod small-end bore with a 50/50 mixture of molybdenum disulphide grease and clean engine oil.

17. When installing the pistons onto the connecting rods, make sure that the 'IN' mark Is on the same side as the oil hole in the connecting rod. Install a new circlip In one side of the piston (do not re-use old circlips). Line up the piston on its correct connecting rod, and insert the piston pin from the other side. Secure the pin with the other new circlip. When installing the circlips, compress them only just enough to fit them in the piston, and make sure they are properly seated in their grooves with the open end away from the removal notch (see illustration).

18. Install the piston/connecting rod assemblies (see Section 22). Reassemble the crankcase halves (see Section 20), install the cylinder head (see Section 10), then fit engine into the frame (see Section 5).

24 Piston rings -

inspection and installation

1. It Is good practice to renew the piston rings when an engine is being overhauled. Measure the pistons carefully to ensure you get new rings of the correct size.

2. Before installing the new piston rings, the ring end gaps must be checked with the rings installed in the cylinder. Lay out the pistons and the new ring sets so the rings will be matched with the same piston and cylinder during the end gap measurement procedure and engine assembly. Identify the top and

23.17 Ensure the circlips are correctly seated in their grooves

second compression rings (see illustration 24.13).

3. To measure the installed ring end gap, insert the top ring into the cylinder and square it up with the cylinder walls by pushing it in with the top of the piston. The ring should be about 20 mm from the bottom of the cylinder. To measure the end gap, slip a feeler gauge between the ends of the ring and compare the measurement to the specifications at the beginning of this Chapter (see illustration).

4. If the gap is larger or smaller than specified, double check to make sure that you have the correct rings before proceeding.

5. If the gap is too small, it must be enlarged or the ring ends may come in contact with each other during engine operation, which can cause serious damage. The end gap can be increased by filing the ring ends very carefully with a fine file. When performing this operation, file only from the outside in (see illustration).

6. Excess end gap is not critical unless it exceeds the service limit. Again, make sure you have the correct rings for your engine and check that the cylinder is not worn. Cylinder wear will be apparent by measuring the ring gap near the top of the bore and comparing it with the measurement from the bottom of the bore (see Section 31).

7. Repeat the procedure for each ring that will be Installed in the cylinder. Remember to keep the rings, pistons and cylinders matched up.

8. Once the ring end gaps have been