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Feasible or not, it still puts you in the same place as the Guardian: When it triggers, your engine is already full of metal and is toast; you just paid more money to find out than the guy who waited until it stopped running..............

How big metal piece it needs to be to be detected and trigger the alarm?

My thinking of the bearing failure - it starts, initially, slowly. Small pieces of metals will be present.
Then, when the rings start coming of, or balls disintegrate - larger chunks will float.

At what point the cam deviation will be seen? So far I do not see it happening as long as all balls are in place (last leg of failure process).

I just wish there was a way to easily inspect the bearing... scope it somehow or so.

The Guardian saw ferrous metal only, and the size was rather small, as is usually the case with ferrous debris in these engines.

Cam deviation values can be seen at any time the engine is running if you have the right scan tool. Normal values are +/- 6 degrees. In the early stages of IMS failure, the deviation values swing wildly back and forth, and at higher values, indicating that the VarioCam system is losing control of the cam timing because the IMS shaft if moving, causing the long chains to go slack.

Quote:

Originally Posted by JFP in PA (Post 638503)

Actually, IMS failures remain "the silent death" right up to the moment that the engine jumps time and pistons start hitting valves. We have seen an absolute ton of metal in the oil of cars that were in for regular oil change service and still running just fine. When you pull the sump cover, there is metal everywhere, so the engine is done at that point, and then I usually had to make a difficult phone call to the owner, who was totally unsuspecting.

And the IMS bearing does not tear up the engine case, it is totally inside the IMS shaft.

Well my engine sounded like a running washing machine full of rocks with no water in it when it was shut down. It was rebuilt and the damaged parts that had to be replaced were a timing chain paddle, the actual IMS, the oil pump and a few bent valves. I suppose it was caught at the exact right time, there wasn't a lot of metal in the engine. The lifters and oil cooler were replaced too, to be certain there were no stray metal bits to wreck the rebuilt engine.