I'm looking at a dirt cheap Explorer 4.0, has been sitting for 2 years. Runs nice, with a double "knock" noise but quieter than a rod knock. Idles smooth at 600 rpm, "knock" is consistent, but increases as engine increases speed. Has 2 year old oil, and 2 year old gas. Would a tune up help it, and revitalize it, or is the engine almost dead. Still drives, didn't push it to hard. Interior is 9/10, exterior is 10/10. I have him down to 600. 4x4 works, and feels good. What do you think? Thanks in advance.

 

Is it a higher pitch sound? Timing chain tensioners about to go? They are not cheap or easy to replace as the engine has to come out. It's priced right if its as clean as you say and you plan on an engine soon.

 

Timing chain has come up in conversation a few times as the most likely issue, how long would I be able to drive it for with that issue?

 

Anywhere from 0 to 100,000 more miles. I would guess on the lower end of that scale. One way to see if your tensioners are toasted is to take off the lower stamped oil pan and see if any plastic chunks are there or sucked up into the oil pickup. Some of these get ruined by oil starvation from the tensioner pieces instead of the chains actually failing. Good thing is that any 4.0 SOHC will bolt in as a long block regardless of what the interchanges say. You want one from at least 2002 or newer. Newer the better.

 

I have found a replacement engine already, but I don't know if I want to buy it knowing it needs an engine, unless the price is in the range of 300.

 

These engines are in demand and sell high. I plan to pull the heads off the one I'm pulling and fix it. A 129k engine with heads just done is worth holding on to since I have two with this engine now. If you don't need it to drive right away, just pull the engine and do the chains yourself. It's parts plus a 200 dollar tool to set up the cams.

 

I was reading up on this earlier today in response to another thread. The issues with the tensioners appear to be:

All years: The springs for the tensioners don't age well. Loose chains follow, and disaster is not far behind.

Up to 2003: Tensioner plastic falls apart, adding to the noise, loose chains and eventual disaster.

Oddly, some on here report 300k on those motors, even old ones.

YMMV.

IMO for the OP, even $600 wouldn't be bad, but beware the trans and chains can make it a $5000 vehicle. That said, if the rest of the motor is sound and you "fix" the chains and you do a new trans (which you probably won't have to right now) you will have a pretty solid runner for another 100k or better.