The '97 5.9L magnum V8 didnt have one when i tore it down but it seems like there is too much slack in the new timing chain (maybe about 1/8 inch). Should I go ahead and get a tensioner? If so, what exactly will it do for longevity and/or performance? Thanks.

 

The tensioner was a fix for the timing chain noise. If you have it apart I would change everything. I did a new chain sprokets and tensioner. The noise went away and runs great.

 

The timing chain noise/slap was a problem and jumping a tooth on the gears from a loose chain was definitely a problem indeed with the 3.9 V-6 `s -- not so much with the V-8`s -- and your right , the tensioner was the fix for it as it kept pressure on the chain to keep it tight as it wore with the mileage . Also replacing the timeing chain with a double roller one from the V-8 was a fix too , i put both on my 3.9 V-6 , probably overkill but i know i wont be worrying again about it anytime soon ! I had no slop/play in the new chain & gears when i put them on the engine , it was almost difficult to get them on together ,, the tensioner is held out of the way untill you pull the pin for it after you get the gears and chain on ,, so if you have slop with a new chain and gears -- something is wrong somewhere -- and a tensioner will be just a band-aide for the problem , just my !