I'm sure a video from Shawn will help, but how exactly does the friction fit become stronger over time?"The hpfp gear only is held on by bolt pressure and there is nothing else holding the hpfp gear to the exhaust cam gear other than just friction? There's no pins, keyways, dowels or nothing, so that bolt torque slightly changes, bam the cam timing gear slips and valves start smacking the tops of the pistons."
This isn't news nor a design fail. Every modern european diesel uses this type design. VWs, Jeeps, BMWs etc. They are all friction fit without keyways held in with one bolt. I've worked on motors with 600k plus on them with this setup, so it doesn't cause one bit of concern to me.
The question is why did the gear slip. Over time the friction fit will become stronger, not weaker. It is a one-time use bolt, however. Was this bolt every removed and reinstalled? That could cause this.
There aren't enough engines with 100k+ miles on them to make any conclusions about design flaws or patterns. That being said, for those who want the extra security, it might be a good idea to swap out that bolt every 100 or 120k miles....
And you really should change the title of this post to: "Exhaust Camshaft Slipped Time & Caused Damage." If the slip was small and you have tapping that means that the valve is still intact. It might be possible to remove the head, put in new valves, and be back on the road.
Moparecodiesel is relating his opinions, as are you. We are left to interpret each, not as an absolute, but as an angle, no matter the intensity of which they're expressed.I hate to be harsh, but the fervor you are flaming up here doesn't seem warranted. There isn't a catastrophic design issue, your motor didn't fail, and I don't think you needed to put in a whole new engine.