First of all: every manufacturer in automotive business has some bad and some good designs. All of them. Period. So there is no need to start any brand wars here.
Today we are talking about Ford’s design and it will be 5.4 V8 engine (aka Triton, although there is a whole bunch of engines in Triton family). By all means it is not a bad engine, you can’t call “bad” an engine with at least 300 bhp of power and 365 lb-ft of torque. But it has one tiny flaw in it that WILL cause expensive consequences.
Here are two timing chain tensioners from that engine, one is old and another one is new.
It operates by a spring backed up by the oil pressure, this is quite typical design on many different engines. The problem with Ford’s one is the seal around hydraulic chamber, where the tensioner is mounted against the cylinder head flange
The seal is white stripe on the new part and brown on the old one. Material of that sealing stripe is not good enough to withstand an environment inside the engine and it gets inevitably (!) deteriorated. Sealing stripe gets flattened out…
and oil under pressure starts finding a way to escape. Sometimes seal can burst in one spot, sometimes it develops small leaks all around the sealing surface as it happened on this one
When this happens we got a problem. As the oil escapes from the tensioner it is in short supply to all the parts that are sitting above it. Among them will be the camshafts and cam phasers. Now if you google for “cam phasers” fist thing that comes up says “5.4 cam phasers… what goes bad?” ;-). And this is when the absolute most of the people realize that they have some problem in the engine. Sometimes it will be just the noise (clapping, ticking, or even “sounding like a diesel”), sometimes it will be accompanied with engine light on or it might be an engine light on without the noise. If you try to ignore this problem for a long enough time you will get this:
Those are surfaces of the camshaft bearing and its cap in a cylinder head. Normally they supposed to be silky smooth, but once the oil flow gets insufficient to them due to loss of oil pressure on top the engine they start to wear down and gets damaged. Once you got them scratched like this, they are done. The only repair is to replace cylinder head with camshaft. In extreme cases metal shavings contaminate the whole lubrication system of the engine and then new engine is the only remedy.
There is lots of talk on the internet and around the garages about replacing the phasers, VCT solenoids, chains, guides and so on. There are also “phaser lock-out” kits available on the market (plenty of those, actually) that claims providing a cheap “fix” for the problem. The later one is the worst solution as it is not repairing anything but only removes the symptoms – noise and engine light. It is like if you swallow a lot of painkillers if you got a broken finger instead of going to the doctor, applying a cast and so on. Might seem attractive as a low cost “solution” but you just keep damaging your engine silently in this case (plus you get very noticeable loss of performance with disabled VCT system)
With the loss of oil pressure to the top of the engine cam phasers gets damaged next, that is true. Without oil pressure to dampen movement of internal parts in the phaser it is subjected to internal impact loads and eventually gets broken too. There is a relatively quick way to replace phasers only without stripping apart half of the engine but again this is not a proper repair (neither it is cheap anyway). New phasers will be still operating under lack of oil pressure and surely will be broken again sooner or later. If camshaft bearings are damaged they will also bleed oil pressure so even less will be left for the newly installed phasers to operate with.
The proper repair MUST include replacement of timing chain tensioners and check of the camshaft bearings condition. Also oil pressure check needs to be done although this is mostly to determine overall condition of the engine and oil pump.
It is worth to notice that while the loss of oil pressure happens on top of the engine oil pressure warning light or gauge will not indicate it as oil pressure for the switch or gauge is taken from the bottom of the engine. Also its worth to know that oil pressure “gauge” in the instrument cluster on F-150 is not actually a gauge. It does not MEASURE oil pressure as there is no pressure SENSOR on the engine but merely a single contact switch that is set to close and open contacts at certain pressure. Therefore “gauge” in the instrument cluster operates in the same way as oil pressure warning light and only has two positions, like “normal” and “low”.
While I mentioned “repairs” here all the time, the smart way is not to wait until you need a repair but rather replace both timing chain tensioners before they allow oil pressure to escape. There is no set interval when this happens but from what I have seen personally in most cases these issues happen between 100 000 and 200 000 km. It does not mean though that this will never happen before that or that none of those tensioners will go over 200 000 km without an issue. Surely $1000+ job to replace two small tensioners is quite a lot for preventive maintenance. Especially when it is not specified by manufacturer but instead the recommendation comes from some relatively unknown guy in Grande Prairie, Alberta (which is “from the middle of some freezing cold nowhere” for the most of the world ). In this case you are welcome to wait until you need new phasers ($3000+), new cylinder heads ($4000+) or a new engine ($8000+)
P.S. There is plenty of much cheaper parts then OEM Ford ones for this job if you check on Ebay, Amazon or Aliexpress. After you’ll have this job couple of times with these cheap copies of the real parts you will realize that OEM parts where in fact the cheapest option all this time ;-).