I've not posted for a long time, but thought I'd provide an update on one of the two Teneres that we bought for a RTW trip in 2009.

My Tenere is fine, and still going strong at 50k miles - with just standard oil and filter changes, and valve check at about 35k miles .

My SWMBO's Tenere on the other hand has not.

At 45k miles we went on a tour of Scandinavia - upto NordKapp and back - a trip of 4.5k miles.
About 2k miles it started with an unhealthy rattle - much umming and erring, and listening to then engine with the clutch engaged and disengaged, and no one could work out if it was top-end, bottom-end, gearbox, or what.
At a campsite we pulled off the camchain cover - all ok. Removed the clutch - all ok. Removed the alternator cover - all ok.
With little option - we continued. It didn't burn any more oil, there was no loss of power. It just rattled so badly that children in the streets were running for cover ;-)
After another 1000 miles or so, we took it into a Yamaha dealer, who was also stumped - his only recomendation was to put it in a crate and send it home ! We carried on.

Back in Blighty, after 2500 very loud and rattly miles, we were in a position to have a more detailed look. I removed the engine ready for dismantling. Removed the clutch side and primary drive, and discovered the primary drive nut was loose (tab washer still in place). On removing this, the cause of the noise was discovered - a badly worn main bearing. The crankshaft can be rattled within the main bearing - it's so bad you can almost get a finger nail between the crank and the inner race of the main bearing !!!
A new crank is approx �300, and with labour (I don't fancy stripping the topend, and splitting the crankcases), and other parts, fear the bill will be �1000.

All credit to the Tenere for keeping running for all those miles with such severe damage !!

So, what options do I have available to me:
1) Shell out �1000 repair for a bike that is probably worth �2k
2) Break the bike and hope I can get �1000 for the various parts
3) Source a used XT660 engine - but these are fetching �700 odd at the moment.
I'm erring towards option 2.
Ebay here we come...