weird engine problem

[If PigsCouldfly]

I have a 2000 ranger 3.0 flex. Sometimes engine is fine except for low power. Then out of nowhere valves ratlle so bad sounds like it is about to fall apart. Along with this smoke from the tailpipe sporatically. The smoke is not continuous.
Paid a guy to change my motor due to same problem but obviously he didn't change it. No motor id numbers so dont know how to prove it.
He did drop the oil pan, I can tell from the new blue rtv. Just checking to see if someone might know what this is. Hopefully get lucky. Thanks

 

[bucko]

The first thing I'd want to know is what type of engine (if any) was replaced into your truck. Was it supposed to be a remanufactured (rebuilt) engine? Was it just a swapped engine from a salvage yard? Any of these usually come with a warranty. Did you get that paperwork? If not, contact the place that did the engine replacement and ask.

How much did this cost you?