If it is the same as on 1050s, then it is spring loaded. Spring pushes tensioner a notch tighter every time chain has stretched enough. If it is not tightening properly anymore, a new spring (not available from Triumph) or tensioner assy is needed. As a temporary fix one could try to manually push tensioner a notch further. But before doing so you should be pretty certain that the chain is indeed loose; overtightening might result in a hefty bill.
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