4.0 mystery of the century!

[Dustbowl]

Gents!
Hope you all missed me! I've got a right proper dozie here!

I'll admit! I've lways been a die hard AMC man, but this one has got me stumped.

I picked up a $500 special, ZJ, touch more space, creature comforts! .. and I still have a beater XJ taken off the road as scrub basher, due to registration laws in the United Soviet States of Australia, the XJ can not be registered for road use.

So this $500 special, now being my daily driver wasn't firing on cylinder no 4. Cavalier as I am, didn't think for a moment, as no petty issue could hold back my 4.0 experience... oh how wring I was.

I decided to change the head over with a spare, the tappet cover thickly coated with black oily residue on the inside, probably due to the use of incorrect weighted oil, and too lomg between oil changes.

The push rod, had pierced clean through the rocker arm, good laugh, changed the head, replaced the lifter (which looked to be in good condition), reassembled the goods with the correct pushrod, when suddenly...

The new rod is sitting about an inch below the rocker face. Cranking will cause it to raise and lower, however never close enough to touch the rocker.

The cam face looked smooth, either totally fine, or had been machined smooth by the lifter.
However logic dictates everything else in the system would bend break or fail before the cam...

So! how the hell did this happen? And what is the issue? Manufacturing fault in the cam? Black goo stopped the oil from flowing to the lifter and it wore through?

Image taken with the pushrod at full height

[IMG]/http://www.ausjeepoffroad.com/forum/attachment.php?attachmentid=76139&stc=1&d=1502362718[IMG]

I'm at such a loss.

Cheers! Dan

[Dustbowl]

Friend's suggestion: "Did you actually put the new lifter in?"
Uuurmnn hur, I'll check that tommorow haha!
Can't imagine having not done that though...

[Classic Boy]

Flat tappet cams losing lobes is not that rare, usually due to insufficient lube, but exacerbated by the removal of ZDDP additive from most modern engine oils.

Put ZDDP in a search engine and you'll discover its history and the effect its removal is having on the classic car and bike engines, big users of flat tappet technology and alas the old 4.0 AMC engine is also likely a victim to due to its design heritage.