My son recently purchased a 2006 mustang v6 with 4.0, on his way home engine started making a plastic slapping sound in the front of the engine. Everything I have seen says timing belt.

question 1 if we have the timing belt replaced will that be a permanent fix or is this going to be a cycle every few years?

question 2 if we swap engine is there another v6 that will perform better without braking the bank?

 

You have a chain, not a belt. A chain will usually last the life of the engine (150k-200k miles) provided that something like a chain tension or chain guide doesn't fail first.

Before anything, I'd have the engine bay thoroughly inspected to make sure the sound isn't coming from somewhere else. Remove the serpentine belt and start the engine. Don't rev it! If the sound is gone then the chain is probably fine and you need to look at something else related to the serpentine belt. If the sound is still there, confirm it's coming from the front of the engine, not the top or the rear. If it's the front, then a tensioner / chain guide is most likely the culprit.

Now, if the sound is coming from the back of the motor....that sucks. These engines have a timing chain the the rear of the motor as well and in order to get to it, you have to drop the motor...

Should you get a different motor and swap it? If it's a rear chain, it may be a good idea to save you down time but, make certain you go through the motor thoroughly and even may replace the guides and tensioners on the front and rear of the motor before installing it. You can then repair your old motor and sell it to get most if of your investment back from the swap motor purchase.

 

"Plastic slapping sound" suggests that the chain guides are broken; they are a plastic type material. It happens on the 4.0