Wow it was worse than I thought. I've just drained the oil as per the manual instructions and got just 2.4 litres out. Bearing in mind that 2.3 litres of this was the quantity I put in it seems the bike has been running on the residual half litre or so that stays in the engine. Bearing this in mind is there any thing else I should check, apart from the bits very helpfully mentioned above, while the oil is out and the crankcase cover is off? Sorry for all the questions but this is a new adventure for me and I would like to get it right.

Did you remember to drain the pipe in the frame?

This is how you learn, keep asking.

I think so xtrock. I opened both the crankcase plug and the one in the front tube of the frame and removed the oil filter so I don't think there can be much oil left in there.

Ok, if bike have been running on the smell off oil i dont know about the engine condition. How many km are we talking about?

Unfortunately I have no way of knowing how far it has travelled with so little oil. The speedo cable is missing, the crankcase oil plug was badly sealed with a bit of plumber's tape and half of the crank case cover gasket was missing. But I took it on as a fixer and it sounds great and rides great so I'm sure I can overcome whatever damage might have been caused. The heart is there - for me it's just a case of knowing what damage I should be looking for, finding out how to fix it and then getting it back on the road.

Compression test, adjust valves first. When you doing the valves check the cam for wear and colour, what mileage you have on this bike?

Thank you for the advice Bobmech. I've opened up the crank case cover and it all seems tight with no play in the cogs - there is a flap of metal bent over one face of the counterbalance nut which seems to have locked it all in place. Given my lack of experience in bike mechanics would you advise me to leave well alone and not investigate further? Or is it imperative to check the keyways as you suggest?

I would strongly suggest removing the crankshaft and balance shaft nuts and check the condition of the 2 keyways and retorquing the nuts preferably after cleaning and applying loctite to the threads.
To undo and retighten the 2 nuts, the shafts can be locked with a copper coin(being soft) between the teeth of the 2 gears.

Also, to remove and refit the clutch basket, it needs to be held when undoing and tightening the centre nut(if you're not using a rattle gun). Beware- the clutch basket can crack/break if not held with a suitable tool or strap.

If this is above your experience level it might be better to get someone else to do it for you.

Bob

Ok thank you. I'm going to go for it. I've got a torque wrench on order and will open it up, hope for the best and just learn as I go along. At least when I close it all up again I will know there is nothing unknown going on in there. Thanks again for all your advice.

I'm very carefully working my way through this. So far so good. The only looseness I have found so far is in the plastic (nylon?) gear driving the oil pump which appears to have about 2-3 mm play in it. Is that normal? The oil pumps out fine when I hand turn the engine so the pump itself seems to be working. Should I be thinking about replacing the oil pump gear wheel while I've got the thing open?

Sorry to keep hammering on in this thread but I've hit another issue I can't explain while putting the new oil into the bike. I drained the old oil, did all the checks and put a new oil filter in. Then tried to refill with the specified 2.8 litres of oil and found the tank was overflowing at 2.5 litres. I've had the bleed screw on top of the oil filter open but wondered if there could be an air block somewhere else or if the oil strainer (which I gave up on removing) could be totally blocked. I left it for an hour to see if it will drain down but the level hasn't changed much.

Normal. You've filled the frame with oil. Start the bike to get it to go to the bottom, then top op the last amount.

Cool. Thanks Jens. That worked great.