is the 4.0l sohc a non interferance motor?

[black_demon69]

can't seem to find a good answer to this question. some sites say yes and some say no

 

[adsm08]

You can't find a good answer because there isn't one. The valve lift/duration vs compression ratio means that if the valves are timed incorrectly they will hit the piston, which means it is technically interference. Also it has a few hundred dollars of special tools needed to set the cam timing, instead of just some marks on the gears, which is a sign of an interference engine.

The shape of the combustion chamber and a few oddities of that particular valve train mean that when the cam is in a neutraled position (so when the timing guide goes, or the rear jack shaft bolt breaks) the crank can spin 360 degrees but the valves are in far enough that they won't get hit, which is a hallmark of a non-interference engine. I have seen many 4.0 SOHCs that is timing drive failures while running with no bent valves.

This is where the confusion happens.

 

[RonD]

+1 ^^^

Yes, the pistons and valves DO occupy/share the same space in the cylinders, so 100% interference engine.
But timing chain failure on the 4.0l SOHC doesn't always cause bent valves

4.0l OHV(1990-2000) was a non-interference engine

 

[85_Ranger4x4]

4.0 timing chains get sloppy, being off enough to make noise and driveablity concerns is different than the utter chaos that ensues when a timing belt breaks in an interference engine. Pretty rare for a timing chain to flat out break.

I have heard it said Ford never put a belt on an interference engine, so if you have a chain your results may vary.

 

[adsm08]

I have heard it said Ford never put a belt on an interference engine, so if you have a chain your results may vary.

Bull sh!t they didn't. The 1.6L in the Fiesta and Escape is an interference engine with a timing belt. And the belt has to be removed to replace the water pump.

 

[black_demon69]

thanx for the replies

 

[55trucker]

sample photo of a fully assembled head...lobe design allows all valves to be closed when at rest, one would be better off if a chain were to completely break causing the valve springs to snap shut all of the valves rather than a severe *late* timing condition

http://www.ebay.com/itm/REBUILT-PAI...D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

 

[AllanD]

4.0 timing chains get sloppy, being off enough to make noise and driveablity concerns is different than the utter chaos that ensues when a timing belt breaks in an interference engine. Pretty rare for a timing chain to flat out break.

I have heard it said Ford never put a belt on an interference engine, so if you have a chain your results may vary.

Actually Ford DOES NOT DO SO NOW, but that is mostly because they learned their lesson with the original ESCORT CVH Engines which were made famous by their interference issues...

The Current "poster child" for an engine that can destroy itself is the Cosworth designed 3.4liter DOHC SHO V8 engine used from 1996-99 in the SHO Taurus
Some "bright bulb" decided to make the camshaft gears "permanently attached" to the camshafts by pressing a mandrel through the end of the steel camshaft tube and expand it into the ID of the gear and it didn't stay attached reliably....they weren't as permanent as intended....


As for how sloppy the chains can get on a 4.0SOHC I've seen several running engines that allowed their
chains to chew their way through the side of the cylinder head.

It makes what is best described as a godawful racket while this is happening...