22.25 Feed the rings into the bore with care

Installation

22. Install the pistons onto the connecting rods (see Section 23).

23. Clean the backs of the bearing shells and the bearing seats in the connecting rods and caps. If new shells are being fitted, ensure that all traces of protective grease are cleaned off using paraffin (kerosene). Wipe the shells and the bearing seats dry with a lint-free cloth. Make sure all the oil passages and holes are clear, and blow them through with compressed air if available.

24. Press the bearing shells into their seats, aligning the tab in the bearing with the groove in the rod or cap (see illustration 22.13). Ensure the shells are seated correctly and take care not to touch any shell's bearing surface with your fingers.

25. Lubricate the pistons, rings and cylinder bore with clean engine oil. Stagger the piston ring end gaps (see Section 23) and insert the piston/connecting rod assembly into the top of its bore (from the underside with the engine upside down on the work surface), taking care not to allow the connecting rod to mark the bore. Make sure the 'IN' mark on the piston crown and the oil hole in the big-end are on the inlet side of the bore, then carefully compress and feed each piston ring into the bore until the piston crown is flush with the top of the bore (see illustration). If available, a piston ring compressor makes installation a lot easier.

26. Ensure that the connecting rod bearing shell is still correctly installed. Liberally

22.27 Fit the cap and shell onto the corresponding rod, aligning the markings (arrowed)

lubricate the crankpin with a 50/50 mixture of molybdenum disulphide grease and clean engine oil. Fit the connecting rod onto the crankpin.

27. Fit the bearing cap with its shell onto the connecting rod (see illustration). Make sure the cap is fitted the correct way round so the connecting rod and bearing cap markings are aligned.

28. Lubricate the threads and seats of the cap nuts with clean engine oil (see illustration). Fit the nuts to the connecting rod bolts and tighten them evenly, in two or three stages, to the specified torque setting.

29. Check that the crankshaft is free to rotate easily. Check to make sure that all components have been returned to their original locations using the marks made on disassembly.

30. Check that the rods rotate smoothly on the crankpin. If there are any signs of roughness or tightness, remove the rods and re-check the bearing clearance. Sometimes tapping the bottom of the connecting rod cap will relieve tightness, but if in doubt, recheck the clearances.

31. Reassemble the crankcase halves (see Section 20).

23 Pistons - removal, inspection §^

and installation jjt

Note: To remove the pistons the engine must be removed from the frame.

22.28 Lubricate the cap nuts before fitting

Removal

1. Remove the engine from the frame (see Section 5). Remove the cylinder head (see Section 10), and separate the crankcase halves (see Section 20). Note: Once the cylinder head has been removed, rest the engine upside-down on a block of wood to avoid damaging the camchain and camchain guides, and to provide sufficient clearance for the pistons and connecting rods to be withdrawn from the cylinders.

2. Remove the piston/connecting rod assemblies (see Section 22).

3. Before removing the piston from the connecting rod, use a sharp scriber or felt marker pen to write the cylinder identity on the piston crown, or on the inside of the skirt if the piston is dirty and going to be cleaned. Each piston should also have an 'IN' mark on its crown with corresponding large valve cutaways which should face the inlet side of the engine (see illustration). If the 'IN' mark is not visible, mark the piston accordingly so that it can be installed the correct way round.

4. Carefully prise out the circlip on one side of the piston using needle-nose pliers or a small flat-bladed screwdriver inserted into the notch (see illustration). Push the piston pin out from the other side to free the piston from the connecting rod (see illustration). Remove the other circlip and discard them as new ones must be used. When the piston has been removed, install its pin back into its bore so that related parts do not get mixed up.

23.3 Note the IN mark which faces the inlet side of the cylinder

23.4a Prise out the circlip ...

23.4b ... then push out the pin and remove the piston

2«40 Engine, clutch and transmission

[■TTW53 If a piston pin is a tight fit in iltiLisi the piston bosses, soak a rag

HilUT

23.6a Using a ring removal and installation tool

in boiling water then wring it out and wrap it around the piston - this will expand the alloy piston sufficiently to release its grip on the pin. If the piston pin is particularly stubborn, extract it using a drawbolt tool, but be careful to protect the piston's working surfaces.

Inspection

5. Before the inspection process can be carried out, the pistons must be cleaned and the old piston rings removed.

6. Using your thumbs or a piston ring removal and installation tool, carefully remove the rings from the pistons (see illustration). Do not nick or gouge the pistons in the process. Note which way up each ring fits and in which groove. The top and second compression rings have different profiles and they must be installed in their original positions if being re­used. The upper surface of each ring is usually marked at one end. This information will also be required if you are fitting new rings (see illustration).

7. Scrape all traces of carbon from the tops of the pistons. A hand-held wire brush or a piece of fine emery cloth can be used once most of the deposits have been scraped away. Do not, under any circumstances, use a wire brush mounted in a drill motor to remove deposits from the pistons; the piston material