I had my 89 XJ listed for sale and one person that stopped to see it decided to not buy it but, since he had retired as a mechanic for Phil Long Ford in Colorado Springs, CO, he suggested I pull the cam out and check it.
He said that over the last few years he had worked there had been several Jeep 4.0 engines came in with bad cams.
The cause?
The EPA's ban on engine oil with zinc additives.
Zinc works as an extreme high pressure lubricant for flat tappet style valve lifters (non-roller lifters) and prevents premature wear on the cam and lifter faces.
A new cam is on order thru Auto Zone but I'm going to start using a zinc additive or a so-called "high mileage" oil with Zinc from now on out.
Budd