Yes, very few compared to the number they made WITH MDS, lol. Hence my use of the word "statistically" in the response. Think how many millions of MDS HEMI's were manufactured and out there, then, during the same timeframe, how many were made without MDS? it's very few in comparison.
Yeah, I suspect some folks with autism on here (of which I'm not one) won't be pleased with that comment, you might want to report it so the mods can delete it.
The issue seemed to really come to be around 09+, when they introduced VVT. I suspect this is when they changed lifter suppliers (and camshafts), as before this, with or without MDS, lifter failure didn't seem to be much of "a thing", if at all.
Let's use some made up numbers here to explain why it appears that way. '09+, we are looking at the 6.1, 6.2HC and the 6.4 with a stick, plus however many non-MDS 5.7'S were produced for HD applications before the switch to the MDS 6.4L. Not a huge number. Let's say total production was around 200,000 for the sake of this exercise.
We'll say MDS HEMI's for the same period, which appeared in the Charger, Challenger, 300, Durango, Grand Cherokee, RAM 1500/2500/3500, Aspen and Commander and includes both the 5.7L and 6.4L mill is 8,000,000 (RAM production is ~6 million since 2009).
Let's say the rate of failure is 0.2%, so for every 1,000 sold, 2 of them will have lifter failure.
- For non-MDS engines that means 400
- For MDS engines that means 16,000
So, in the above example, there were 40x as many MDS engines made during that period than non-MDS, so you are of course far more likely to hear of or know of lifter failure with an MDS example than with a non-MDS example even if the rate of failure is identical.
According to a very informed FCA tech on here,
@TeamZero, he has confirmed that it's a materials issue with the lifter roller and/or pin. The defective ones are improperly hardened and so the needles eventually start to wear a groove in the roller or the pin which stops them from rolling around with the roller and once the groove/ditch becomes deep enough, the needles pile-up, which stops the roller from rolling, at which point it wipes out the cam lobe.
There have been MANY revisions of the lifters at this time, supposedly the issue has now been fixed. The newer lifters have larger, fewer needles as one of the changes.