4.6 rattle from front of engine?
 

Just out of the blue I started to get a rattle sound from the front of the engine. At first it was only intermittant at idle. Now it is pretty consistant at idle but you do not hear it at road speed. There is almost a kind of squeal or screech when you first hit the key, kinda of like a slipping belt but you do not hear that after immediate startup.

The engine runs smooth. There is approx 86k on the motor. It carries a heavy load but gets driven very gingerly. It is definitely a noise of something going around and contacting something. Almost like a fan blade hitting something.

I've checked the fan and clutch, they are smooth and tight. I thought it might be an idler pulley or the belt tensioner but I depressed the tensioner and spun it's pulley as well as the idler pulley and they seem smooth and tight.

I am beginning to fear that the motor has lost a timing chain guide and that I am hearing the timing chain knocking around.

Could this be likely? ...and if so, how big a deal is it to get to it/them with the engine in the van. Kinda looks like I would have to pull the radiator at minimum.

I think your diagnosis is correct and you have a good bit of work ahead of you. If you can get the pan off you could do a more certain evaluation. If you find a lot of plastic in the bottom you will have your answer to the noise. You should be able to replace the guides and tensioners from the front. It's a lot of work but less than pulling the engine.

I found a good youtube video on changing out the chain tensioners (motor in) I can post the link if anyone is interested.

HOWEVER....

Today I did a little more investigation. Even though the noise sounded like it was coming from the front of the engine, it was coming from the back. Turns out, my flywheel is broken. We pulled the inspection plate, grabbed the torque converter flywheel and it wiggled back and forth.

I took it to a transmission shop and they confirmed it. It is being worked on now. I think it is a 6 bolt Romeo.

Thanks.