Ok so I've got a rattle on cold startup, started around the time that I changed my oil. I had a significant leak due to the oil not being threaded on properly and I had to change it again to make sure everything was all good(The threads for the filter are a little bit damaged but it still holds when you're particular about it). I heard the rattle when I started and got the leak and I immediately shut it off and rechanged. Now it has the rattle on startup. I assume this is a timing chain issue, can someone provide some info on what to do? What happens if I just leave it? How big of a pain is it to fix?

 

You can try installing the two long chain tensioners, ASAP, use new Motorcraft units, yes they cost more but worth it in this case, make sure to PRIME THEM before installing, dip in oil and pump them, they will get rock hard

If you still have the rattle then chain's guide is broken and it will get worse over time, if its the rear passenger side guide then engine will need to be pulled out, front guides can be changed in vehicle.
You would have had to buy new tensioners when replacing guides so not a waste of money to do it now.

If you leave it guides will break, and rattle will start to happen at most RPMs, long term it just gets worse and worse, and chain could break, and the 4.0l SOHC is an interference engine, so valve and pistons can hit which means bent valves, usually pistons are OK, usually

 

I've got a small rattle at acceleration as well, I didn't think it was related but maybe it is. Disappears when cruising, even at high rpms. Sounds like a playing card in spoke of a bike wheel, doesn't sound that bad. I will try replacing the tensioners as soon as possible, is there a specific tensioner that I need? Thanks for the help. The sound is only for about a second on cold start, it isn't prolonged. Its not the same sound as the accelerating sound

 

You need these: https://www.ebay.ca/itm/Ford-4-0L-Ri...-/191450881556

For now use Clear Flooded Engine for start up

Turn key on
Press gas pedal down to the floor, and hold it down all the way
Crank engine and count to 5 while it cranks, then release gas pedal, and engine should start with no rattle, hopefully


Clear flooded engine is in all fuel injection computers, it allows you to crank engine with Fuel Injectors OFF, but spark is on, which is handy for several tests, lol, but also to clear gasoline out of a flooded engine

With key on, computer is on
When you press gas pedal down to the floor the computer gets 4.5 to 5volts from the TPS(throttle sensor)
When computer "sees" WOT(wide open throttle), at 0 RPMs it enters Clear Flooded Engine routine and shuts off injectors
So you can crank the engine without it starting, as long as you want really, lol
But as soon as you release gas pedal injectors will start

You are doing it to build up oil pressure in the tensioners BEFORE engine starts, I do it for the same reason but on my High Mile(400k) 4.0l OHV, to get bearings oiled before start up, so I use it every morning
I do it for 5 second, you can do it longer or shorter, up to you


The difference in price for Motorcraft and 3rd party is BIG, but I really think for something like this you should go with Motorcraft(Ford)