Continuing the discussion from Engine Timing off by 10 degrees:
I’ll move here and repost this in what I hope is an informative way. This is better-researched and documented than my last response, which I deleted as I thought it largely vestigial to the thread.
Loss of oil pressure does not equate to loss of timing chain tension, even with a “hydraulic” tensioner as seen in the Ford “modular” engines, of which the Lincoln Navigator 5.4 is one. It is true that they are fed engine oil from a pressurized source (i.e. an “oil galley”). It is true that this provides a portion of the mechanism by which timing chain slack is removed, i.e. tensioned*. However, the inverse is not true, which is to say that loss of oil pressure does NOT put the slack back in the timing chain. If this were true the chains would be at full slack each time the engine is started up, which would almost certainly be catastrophic in very short order.
Here is a lovely video a colleague found showing the ratcheting mechanism which prevents the tensioner from “detensioning” being manipulated to allow retraction during a chain change.
This ratchet prevents the loss of oil pressure from detensioning the chain, at least until wear limits are reached and/or something is broken.
* The remainder of the mechanism is made up of a spring and the mechanics of timing chain function.
I hope this helps clarify how these timing chain tensioners function, as the misconception appears to be quite widespread (and some nicely written, “official sounding” articles, such as that posted by hasbridge, make it seem so feasible).
EDIT: See below for Hasbridge’s corrections to the real world as-is instead of as-I-know-about-it. Turns out they DO use “purely hydraulic” tensioners, which are asserted to work similarly to hydraulic valve lash adjusters (and I have a whole new tangent here, too, which I shall spare you) with no ratcheting mechanism. They may or may not be in the 2003 Lincoln Navigator which I think has a DOHC 5.4 litre “modular” V8 from FoMoCo, though I could be wrong there, too. Either way, Mr. Falgout’s is broken, and the fact that Ford actually made a design which COULD be affected directly by oil pressure makes my assertions above less valid, and the notion that low oil pressure/volume due to overfilling and aeration more valid.
None of this fixes Mr. Falgout’s problem, but does increase my curiosity as to what actually happened. My BS meter is still off the zero mark, but less close to the FULL mark.
Also, just realized this should be a DOHC motor, so the timing components should look more like this
which I borrowed from this guy’s thread if you want to read about assembling a Cobra engine.
As far as I can tell, being SOHC or DOHC has no bearing on the plastic/cast iron tensioner situation.
