Having viewed several forum discussions of timing chains adjustment procedures and mechanical problems posed, I felt this thread should be started and facts and myths be explored for what they are...
The NHT has two main sub groups having both twin chain,then later single chain versions.
Both NHT configurations have 4 cam lobes and are the main four chain loading events contained within two crankshaft rotations. These two crankshaft rotation have an affect that will be expanded upon later
Each of these loading events cause a pulling forward then transitioning to a restraining of reverse rotation of the camshaft.
These dynamic rotational movement actions are affected by the chain freeplay which has a maintenance adjustment procedure.
These maintenance procedures and the running conditions and tolerances are affected by the hardware that is implemented. Specifically the early twin chain bare steel tensioner NMT2217.or later 06-1094 for single chain engines.
Later rubber layered tensioners, twin chain 06-4647 and single chain 06-7574 versions of the tensioner significantly change the dynamic of component wear and adjustment procedure between these two different material types.
The original steel tensioners wear mode is for the outboard coupler links and the inboard roller unit links to ride directly on the face of the steel tensioners. Wear originates on the riding edge of the side plates. The material has the ragged surface the typical result of a sheer punched process. This face eventually is burnished down to a smoother running surface.
The wear from this burnishing process is reflected in the four groove faces, two inner and two outer, on the steel tensioner.
The next significant change is to the rubber facing of the tensioners. The change of wear mode is now that the coupling side plates and roller side plates will saw into the rubber and "bottom out" and now support the chains movement action on the actual chain rollers on rubber. A down side is possibly a quicker and much larger bedding in process requiring a more frequent initial maintenance interval until the bedding in process is completed... .
