17. The front slipper blade is mounted into the barrels and retained by two M6 screws. On this engine the rubber face has become separated from the alloy blade and will have to be replaced. Apparently this is not an uncommon problem on XS650s and is worth checking at every top end strip.

18. The oil pump follows conventional Japanese design and consists of two concentric rotors running in a carefully machined housing. Unusually the XS650 oil pump lives inside the clutch cover, and the tacho drive will have to be removed first to access it. Check carefully for score marks in the housing and rotor faces, but if any damage is evident the clutch case itself may have to be replaced.

19. While the tacho drive is apart check for this tiny oil seal which stops engine oil escaping and leaking out from the tacho cable. The threaded part of the cable mount screws out and the oil seal presses into the housing beneath it.

20. The gear cluster shouldn't usually give much trouble, but older XS650's can sometimes develop a fondness for jumping out of gear. Careful inspection of these dogs should reveal any problems, rounding or wear on the pins indicating a problem. I don't normally strip gears from their shafts unless strictly necessary, but if replacing a single gear cog support the gear shaft upright in a vice and carefully remove each gear, circlip and washer before replacing in the same sequence.

21. Any gear selector problems can usually be traced to the selector forks. Watch for excessive wear or signs of blueing due to excess heat on the fork tips here. Bent selector forks will fail to engage the gears correctly and should be replaced.

22. The kickstarter mechanism is a pretty sturdy affair and is unlikely to give problems, though this is a good time to replace the return spring if it has been showing signs of weakness. The drive gear shows signs of polishing on the teeth but this doesn't look excessive.

23. The starter bendix gear looks to have had a rather harder life, and is showing signs of wear on the edges of the teeth which engage with the crankshaft. However looks can be deceptive; the gear teeth are actually relieved as part of the manufacturing process to help the starter engage. Though some wear is evident I consider this gear still serviceable, and we'll be re-using it.

24. The old sump filter (right) proved to have a piece of gauze missing. Not only was this not filtering the oil as it should, it also makes me wonder what happened to the missing piece! However as no signs of foreign bodies were evident in the engine I'll simply replace it with a new one (left).

25. Final thing to check before the rebuild are these two carbon brushes which fit onto the alternator stator and bear against two copper tracks on the rotor. Excessive wear on these brushes is a common cause of charging problems on these bikes, and is easy to overlook. These are about half worn, and should be good for a lot more miles.

And that's all the bits sorted out. The engine has proven to be in better condition that we'd expected, and I'm wondering if Lorenzo's original problem was down to a carburation fault as evidenced by the excessive carbon deposits in the top end. Reconditioning the valves should help it to run better, and we've decided to replace the camchain as a precaution while it's being rebuilt. Next month I'll be clearing the workbench and bolting it all back together. Thanks to Paul Coward at Bikerworld (tel 01422 844681 or 07944 698793) for the bead blasting.