17. With the engine supported on the workbench I can now proceed to strip the top end. Firstly the cam cover unbolts and lifts clear, revealing the single overhead cam and two-valve-per-cylinder engine layout. The cam followers remain captive in the cover, at this stage I'll put the whole assembly aside for examination later. The outer four cylinder head nuts sit atop rubber washers, these need to be replaced on the same studs on re-assembly to prevent oil leaks.

18. According to my workshop manuals it is necessary to split the camchain at this stage, and rivet it up again during re-assembly. I have an aversion to riveting camchains, preferring to use an endless chain when possible, so I decided to see how far I could strip the engine without splitting the camchain. The camshaft is supported on two pairs of hefty roller bearings, one pair at each side, and with the camchain tensioner removed there's enough slack in the chain to slide the bearings off the ends of the camshaft. With the bearings clear the camchain easily unhooks from the cam drive sprocket, and the camshaft can be lifted free.

19. Now the remaining three small bolts holding the head to the barrels can be removed, and the cylinder head lifted clear. Note the big screwdriver I've slid into place to stop the camchain dropping into the crankcase as I lift the head clear.

20. Removing the barrels is simply a matter of sliding them upwards and off the pistons. Be careful as the pistons emerge as they can rattle against the crankcase mouth. Again the camchain will need something to stop it falling into the crankcase. I've tied a piece of electrical wire around it and hooked the wire around a casing screw while I lift the barrels clear.

21. Now I can remove the pistons. Delicate work with a set of small pliers gets the circlips out, and the gudgeon pins slide out to release the pistons from their respective small ends. I always discard old piston circlips to avoid the temptation of re-using them, and I've marked each piston by scribing "L" or "R" inside the skirt to make sure they go back on the same rods on re-assembly. If in doubt it's also worth scribing a mark to indicate the front of each piston, though on this engine I've already noticed Yamaha have cast direction arrows on top of the piston crowns.

22. The rear camchain slipper blade is fixed into the top of the crankcase mouth with four phillips head screws which can now be released. And here I finally discover why it's necessary to split the camchain to totally strip one of these engines; the camchain loops around a small tubular brace on the slipper blade mounting. However I have learned that it's possible to strip the engine's top end with splitting the camchain, which should save a few headaches if you just want to do a rebore or valve grinding job.

23. Turning the engine over now, I can remove the bolts which retain the sump and lift it clear. The sump filter is a gauze strainer which can be cleaned off in paraffin and dried off. A small magnetic plate is bonded along the gauze and will also need careful cleaning before re-fitting.

24. A quick check round to make sure I've removed all the ancillaries and it's time to split the cases. Like all Japanese engines, there are crankcase retaining bolts fitted from both the top and the bottom half, and it's important to find them all and remove them before tapping the cases apart with a rubber mallet. With the joint split, the lower casing just lifts away and leaves the crankshaft and gearbox shafts in the upper casing.

25. And finally the crank and gear shafts lift out. Just to prove a point I've left the camchain in place while I lift out the crankshaft. So it's even possible to remove the crank without splitting the camchain, should you so desire.

Next update I'll be taking a good look at the parts from the stripped engine to see what needs replacing for the rebuild.