Secondly - I've got the 900 one to work. There's a HUGE difference in the spring tension of the plunger between the 850 and 900 - the 850 is a ratchet type with a strong spring and the 900 a worm and nut type with a very weak spring (well mine was)
I don't have a diagram of pic so it's best to PM me and I'll give you my phone number to talk through it but the 900 has a "Slinky" type of coil spring, if that makes sense, the kind of action you'd get in a clockwork toy. I basically dismantled the tensioner assembly and rebuilt it with a couple of more turns of tension, much like winding a clockwork toy up just that bit more (I realise some of the yoof on here won't have a fuckin' clue what I'm on about talking about clockwork
)This gives the plunger some more pressure on the chain tensioner blade and so far (fingers crossed) and 50 miles later there isn't a noise from it
Seems to me that this is a Yamaha production assembly fault even though Yamaha UK have only replace two TDM900 tensioners under warranty 
To determine TDC firing on the left cylinder - and without having to take the camcover off (again
) you can remove the cylinder identification sensor out on the top left of the cam cover (this picks up a signal to tell the ECU the left cylinder is firing) and put your little finger down onto the camshaft. Turning the crankshaft in the anticlock (forward) direction you will feel a raised part on the exhaust cam as TDC is approaching - then turn the crank 1 FULL TURN from there and that's the left cylinder firing. I also removed the right spark plug to feel compression to back up this theory/practice but the cam sensor method works 
