Well, I know I'm reviving an old thread, but all the rest I've found were either for a complete 4.0l swap or had very few posts. I'm having a hell of a time getting my 4.0l head to seal on my 4.2l block after a rebuild. I bought the Jeep (in my sig) with the work already done so I can't tell you any more than what's in there. In Aug 2012 I blew the engine, and it sat through the winter. I had the block bored 0.030" over, crank ground, and a complete head job including new valve seats. I'm on the 3rd head gasket (1 that came with the 4.2l engine kit, and 2 Fel-Pro 4.0l) and can't get it to seal without leaking. The 4.2l gasket was obvious, but both 4.0l gaskets let small trickles run down the driver side of the block. I checked the block & head with a straightedge and can't fit the smallest blade (0.05mm) in at any point with any orientation of the straightedge. I found out about the Hesco kit here and have a few questions for anyone who can answer them.
1) On the Hesco website it looks like only the very outermost coolant jacket ports are filled in. Is this because they're outboard of the head bolts and more susceptible to leak? We have several really good welding shops here that I could have do the welding for me, then bring it to my machine shop to be planed.
2) After reading about the intake ports I dry-fit the intake to the head and noticed the poor clamping with the stock cupped washers. It seems like guaranteed vacuum leaks to me, which would definitely explain why my engine ran so erratically. What does Hesco do to modify the head for use with 4.2l intakes? Will a Clifford intake fit and seal tightly without the modifications? How about other brands, like Offy? Will any year of 4.2l intake fit correctly? I'm running a Weber 32/36, I wasn't impressed with it and was considering going with a Motorcraft but after reading this thread and discovering things about my engine I'm sure the carb was never the issue.
3) How about a cam swap to take advantage of the 4.0l head's better flow characteristics? I'm running stock cast pistons and can't tell you how much was removed from the head & deck, but the machinist said it'll still run on 87 octane. I've been told swapping to a. 4.0l head is a bolt-on 40hp and that with the right cam & jetting I'll see a nice increase in torque off idle as well, I might as well take advantage of it! If I can't get this thing right on the next try it's coming out and I'm swapping a diesel in like I should have done in the first place!