The XS Yamaha's would adjust while the motor ran. A plunger would move in and out as chain slack moved it. When properly adjusted, the plunger mostly stayed flush with the housing. I like the spring idea-tension without locking, allowing some movement in chain slack without risking inadequate tension.
Not quite sure the plunger moves in and out as the chain slacken....
From the XS11 website...
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Adjusting the Cam Chain Tension
An out-of-adjustment cam chain can cause the bike to run poorly andvibrate. To adjust the tension, locate the tensioner on the front of the engine between cylinders 2 and 3 - it's that little do-hickey protruding from the cylinders with a bolt sticking out the left side. Remove the engine case cover over the timing plates and use a wrench to manually rotate (clockwise) the engine until the timing pointer aligns with the "C" on the timing plate. Then loosen the locknut on the cam chain tensioner, loosen the bolt, then retighten the bolt and then the locknut (specified torque is only about 5 ft/lbs so don't overtighten), and replace the case cover. That's it.
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So it appears to me that the plunger is spring loaded and once you have the timing point aligned with the "C" you loosened the locknut and let the plunger move in on it's own until it bottomed on the guide inside the motor.
Then retighen the locking nut...
The plunger can't move because of the locking nut.... and the tightness of the bolt on the plunger shaft.