Is the 4.0 SOHC an interference engine?

[North Idaho 5.oh]

I know this is going to be a “duh” type of question for most of you guys....
I have been reading a BUNCH of misleading/confusing info on wether or not the 4.0 SOHC is an interference engine or not.
Can someone/anyone give me a definitive answer wether it is or not ?
I lost all compression in the motor of my wife’s truck and I just need to know if I can do a timing kit, or if I have to get another engine... ? Let me know fellas!

 

[Uncle Gump]

It is most definitely an interference engine. Jump a tooth on the timing chain and it is all over. Best case is it bent the exhaust valves... worst case gets much much worse.

 

[North Idaho 5.oh]

It is most definitely an interference engine. Jump a tooth on the timing chain and it is all over. Best case is it bent the exhaust valves... worst case gets much much worse.

Ya that was my fear... the engine only has 140k miles and had no signs or symptoms of weakness. No “clatter” or anything of the such. Just decided to die one day and lost compression... had to get it towed and everything!
Was already planning on a 302 swap but not necessarily this soon.

 

[Dirtman]

If its a timing issue it should still have compression on one bank. It would be a really strange disaster to have BOTH timing chains fail.

 

[North Idaho 5.oh]

If its a timing issue it should still have compression on one bank. It would be a really strange disaster to have BOTH timing chains fail.

I will be doing further diagnosing when the snow clears out a bit. It turns over as if all the plugs have been removed... any other reason it would do that? Head gaskets are intact

 

[Dirtman]

Dunno, my experience with the 4.0 SOHC is limited. Just seems odd not having the famous rattle first, and then loosing both chains.

 

[19Walt93]

I'd do some more diag before you spend a bunch of money, it's unlikely the timing chains would fail suddenly without making noise first.

 

[Dirtman]

You sure the engine is actually spinning and you didn't just shear off the flex plate?

 

[North Idaho 5.oh]

I'd do some more diag before you spend a bunch of money, it's unlikely the timing chains would fail suddenly without making noise first.

That’s what has me confused... I actually own 4 trucks with the 4.0 SOHC ... 1 of which had the rattle and I was able to “save” it by doing a timing kit on it.
Haven’t had one completely fail like this one quite yet...

 

[North Idaho 5.oh]

You sure the engine is actually spinning and you didn't just shear off the flex plate?

Yes. As I was turning the key I saw the fan turning.

 

[RonD]

Good news is that 4.0l SOHC is barely an interference engine, it is one, for sure, but if the cams stop turning and the pistons don't its rare to get bent valves, and never damaged pistons, outside of a mark
The confusions comes the the 4.0l OHV being NOT an interference engines, and there were used in the same vehicles

Chances are the engine is OK but will need to come out to do the timing chains and "maybe" replace a few valves, IF they hit a piston

Picture here of piston strike in the 4.0l SOHC: https://www.explorerforum.com/forums/attachments/3dings-jpg.77924/

Valve were bent for sure, but pistons are OK, IMO
Once engine is out, you can do a leak down test on each cylinder to see if valves were damaged

 

[North Idaho 5.oh]

Good news is that 4.0l SOHC is barely an interference engine, it is one, for sure, but if the cams stop turning and the pistons don't its rare to get bent valves, and never damaged pistons, outside of a mark
The confusions comes the the 4.0l OHV being NOT an interference engines, and there were used in the same vehicles

Chances are the engine is OK but will need to come out to do the timing chains and "maybe" replace a few valves, IF they hit a piston

Picture here of piston strike in the 4.0l SOHC: https://www.explorerforum.com/forums/attachments/3dings-jpg.77924/

Valve were bent for sure, but pistons are OK, IMO
Once engine is out, you can do a leak down test on each cylinder to see if valves were damaged

See that’s the thing .... BARELY being an interference motor and throwing a bunch of parts on a 50/50 chance it will pan out kind of bothers me... I will definitely be tearing into it more as weather permits for sure. My wife is driving my 302 Frankenstein ranger to work right now so it’s all good! ..... for now lol

 

[RonD]

Yes, its all just guessing until you open the box at Xmas, lol

You can't "throw parts at it" until its out, and then you will know why it lost compression, so no guessing on whether its worth while to redo just timing chains

 

[North Idaho 5.oh]

True. I’m just going to be ready for anything.... I’ll be pulling it out in the next few days hopefully, and with pics!