[thom4782]

The hysteria arises because 1) the timing of IMS bearing failures is extremely difficult to predict and the 2) cost of failures is unreasonably high given the market value of these cars.

Data suggests the following failure mechanism is the most likely. IMS bearing seals degrade and allow the internal lubricant to wash out. Unfortunately, the leakage is too small/slow to allow mist engine oil to replace the loss. When this happens, the resulting friction increase leads bearing spallation, which then leads bearing failure.

Timing is hard to predict because contaminants in the oil of low mileage cars that sit idle for long periods accelerate seal degradation. High mileage cars, typically daily drivers that get up to operating temperature frequently, slow seal degradation markedly. Hence, IMS failure occur in both low and high mileage cars. There is no magic number after which these cars are safe.

Single row bearings fail more frequently than dual row bearings because they are more highly loaded and they see the effects of poor lubrication more dramatically.

People can increase their odds of avoiding an IMS bearing failure when they replace the original by taking the following steps:
1) install a bearing that can withstand higher loads, e.g. ceramic over steel, dual over single, etc.
2) ensure that the bearing receives adequate lubrication, e.g. is unsealed so it receives mist oil or is oil fed

In my case, I installed the IMS solution because it was capable of bearing the highest loads, was oil fed, and if it did fail it was the one design that was most likely to keep the engine from jumping timing.