If your rings go bad, or you spin a main bearing, you have to dismantle the crankcase & remove the pistons, etc. Thats not routine, its not done on any kind of schecule, its a major repair. Often its an excuse to replace the engine.

 

Tensioner #9 pushes against chain guide #11. When tensioner runs out of travel, it leaves slack in the chain. Problem is, I dont know whether its spring-loaded or driven by oil pressure. Probably both. Probably have to remove lower timing cover. I havent done this yet...

 

Grab the chain where the #8 label is in the illustration, pull it away from the sprocket.

 

Theres probably a spec for that.

 

The sprocket teeth are so deep like a bicycle chain that it takes a tremendous amount of stretch before it can skip a tooth.

 

Little cover #2 allows you to see the tensioner.
Allowable extension = 13.5mm.