manual camchain tensioner fitment guide

[PieEater]

I thought many bikes had done over 100,000 miles - I assume on the OE tensioner, some over 200,000 miles?

My guess is that failure will be age related rather than mileage related. The spring in the tensioner will be applying the same pressure regardless of whether the bike is being used or not. I just had the spring go on one of my passenger footpegs, and then read this thread and thought if I'd just had one spring go on the bike ..........

But why did Yamaha fit an auto tensioner?  Are there reasons why the tension needs to vary in day to day running?

As you know chains stretch from new, an auto tensioner will remove the necessity for a service item which may get overlooked on the first few services leading to warranty claims. Once a chain has done a few thousand miles it will stop stretching as much so adjustment becomes less of an issue, you're looking at thousands of miles not day to day.

Also how do we know exactly how much tension to apply to the manual unit?

I've just fitted mine, and this part wasn't that straightforward, I think I got it right but might ask a mechanic to double check. when you're tightening the tensioner you can feel when it starts applying pressure to the guide, with the engine running you then start to hear the rattles start to smooth out as you apply more pressure. You need to find the point where all the rattles have gone without applying any excess pressure on the guide, I found this part a little difficult especially with the fan running so I tried a few times and found where I thought the best setting was. Apparently if you overtighten you hear a whirring sound which I never got to hear so I assume all is good as the engine sounds as good as it did prior to replacing the tensioner.