this being the engine that they replaced the mighty /6 with, the 3.9.

working on my 99 Dakota daily driver.
I had to pull the timing cover off, it sprung a leak and the cover is ate out/ corroded, roughly behind the alternator.
It has a tensioner on the timing chain, which is pretty much "tensioned out", the travel is about used up/ at the end of its range. chain is tight on the "pull side", but as much as has had to be taken up by the "slack side" I'm sure my cam timing is retarded. IDK why that V6 was charecteristically so hard on timing chains, especially when compared to the series of V8s that it was derived from. I have seen 3.9s both with, and without these tensioners. and have seen them added to ones that did not originally have them. I am not a fan of a steel chain rubbing on a plastic block. but that's 90% of todays engines. at least this one doesn't have multiple chains, too...… I have never seen a tensioner on a 318 or 360. and this 3.9 takes the same chain and gear setup.

I have a heavy duty double roller here that I was gonna put onto a 360 I am working on that will go onto this engine. Because I have it on hand. . I'll buy another one for that engine. I hope to have this truck a long time and don't want to ever have to revisit the timing chain or cover again because I simply hate redo's. I tend towards "overkill". especially when it's my own and it's no more work to do than to put it back like it "was".

Ive seen 3.9s with, and without, this tensioner for the chain. Being as how a good true roller, double roller chain is so much a better product than what they put on these engines from the factory if you were doing this job, would you put another tensioner on with the double roller? Would the double roller chain "tear up" the tensioner any more than another original style chain would?

I added the Tensioner and a New Chain to my 77 318. It has 120,000 Miles on it in december when I did this Job. The braintrust at Mopar action recommended it for their Performace LA Block Builds.
I got the Cloyes Set https://www.rockauto.com/en/moreinfo.ph ... 53&jsn=496
and added the tensionser and the Moly Fuel Pump eccentric to the truck.

Makes a world of difference. It was like a Total engine rebuild.

The Thing Fires right up and Idles super buttery smooth. Bottom Line I would recommend the tensioner for any A or LA Engine build. I probably will at least re-chain a few more of my LA engines in this manner.


I believe the Mopar LA Blocks have one of the longest center to Center Distance and it tends to kills the chains. I believe the tensioner is a good addition!


Throw your ideas on FABO or moparts and see what happens there too!
Greg

_________________
http://www.youtube.com/hyperpack

LA engines and their derivatives have the same cam-to-crank relationship as the early hemi. The camshaft is raised, and the lifters angled as they are, for hemi valve gear, rather than wedge-head valve gear. Engine machining equipment is expensive dontchaknow.

I think the 3.9 eats timing chains due to the uneven firing order and the resultant harmonic vibrations. If true a much better crank damper would help the timing chain. A belt drive would be better yet from a harmonics standpoint.

The roller chain might be a little rougher on the tensioner than the silent chain, but probably not enough to matter. There are plenty of OHC engines with roller chains and they don't eat tensioners.

_________________
Joshua

Are these tensioners just a spring, or do they tap into the oil line so there's more pressure when the engine is running?

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

just a spring, holding a piece of plastic against the constantly moving chain.

I wonder if the tensioner reduces some of thr harmonics through the chain?


Greg

_________________
http://www.youtube.com/hyperpack

When I tried to pry the tensioner away from the chain the plastic block on that side snapped like a twig, and the chain had over an inch of slop. Meaning that the chain had stretched and the cam timing was definitely retarded.
I started it after I was done, the engine idled slower and smoother than it has since I have had the truck, about 20 k miles.