I just posted this in the Motor Oil Choice. I am adding it here with additional information that pertains to the oil pump drive assembly. I have also trimmed out pieces of the original post.
I'm seeing more and more of earlier Jeeps with the same problem. I'm really starting to agree with the guys at Hesco that this is being caused by reformulated motor oil.
After reading the recent responses I contacted Hesco and spoke with Bennie. Hesco is the designer and provider of many Mopar products and I trust their advice. After a very informative education lesson on engine oil, camshaft gears and flat tappet cams I am switching today to non-synthetic(dino) oil with a ACEA A3 and more ZDDP additives.
There seems to still be an outstanding issue with a lack of proper lubrication to the bushing at the top of the oil pump drive assembly.
I would love to see a response from owners who have experienced the premature cam shaft gear wear with the below.
1. Year of the vehicle and model(Wrangler or Wrangler Unlimited)
2. Length of ownership(Did you buy it new or used? If used how many miles were on it when purchased?)
3. Current millage
4. Frequency of oil change and all oils used
Because our 4.0 straight 6 uses flat tappet cam we need to pay extra attention to the engine oil we use. This also applies to the cam shaft gear on the oil pump drive assembly. According to Bennie this is not new issue and they started seeing the same failures 5 years ago on older wranglers as well as newer ones up to 2006.
The sliding frictional forces are much higher on flat tappet cams compared to roller tappet cams. To combat this we need to ensure we use an engine oil that matches the specifications of the oil it was designed, tested and proven to work with. Remember, we are running an engine that was first introduced in 1987 and has only been refined since it was retired at the end of 2006. ZDDP is an anti-wear additive and high levels of it were in place when the engine was designed and we need to make sure the engine oil we run has sufficient numbers of ZDDP.
In recent years many additives have been removed due to regulations from the EPA; specifically ZDDP(The EPA "claims" the additives increase the breakdown of catalytic converters. This is due to small amount of oil leaking past rings and seals.). In synthetic oils, especially the ones from Mobile 1 it is an even bigger issue. Synthetic oils are more "slippery" than conventional oils and may cause increased levels of wear on flat tapped cams.
This is a consumer education issue and an issue with the oil companies evolving their formula without properly indicating to consumers the oil may cause damage to their older engines. Mobile 1, along with the majority of major oil manufactures have modified their oil formulas to produce the best efficiency in modern engines(Which the majority are now roller tappet cams).