if its never had the update kit or cam chian kit then I bet your tensioner is out a good 20+mm and has lost some tension on the chain. You need to measure the drop in the tensioner plunger to see how far in it is. 16mm and you are suppose toadd a plug to bring back the spring tension. Depending on what style of guide it has you might just be ready for the spacer. If its not the aluminum guide then You really need a new guide which uses more of the circumference of the chain thus making the plunger stay in the tensioner more then it is. You can check the measurement without loosing tension.
1 most important do not start the bike or attempt to turn it over while performing this check.
2 remove center nut from tensioner (just the big center nut leave the two 8 mm hex bolts holding the casting to the engine alone)
Blow is a picture with the tensioner plunger out some as it would be in a bike.
your going to measure from the face of the casting (where your center nut seated the copper washer against) down to the firs tsurface of the plunger.
below is a picture with the plunger in and the ink pen pointing at the surface your measureing down to.
If this measurement is 16 mm or more you need to add a spacer in the plunger. this can be either bought from Triumph or made from a good bolt shank.
the plug for the tensioner is .390" diameter by .355" long. Alternatively, you can stretch the spring out some to take up the difference and increase spring tension.
If your drop is extreme say 20 +MM its time to chn=ange the guide and look at the crank gears for safety. They had a bad batch of them in the early years.
Hope this helps
If I confused anything just ask away.
OH and again whilt the center nut is out of the tensioner do not try to start the bike or turn it over unless you want to buy some new valves and possibly some pistons.
Or worse
