4.0 Head Conversion

I don't know what to tell you other than to say that they're full of crap. =8~> I've been running the head swap with my MPI for months now, and it works great, and has had no problems whatsoever. There are quite a few others who are running the same set-up and have experienced no problems. In fact, one of the benefits of using the 4.0L head with the MPI is that the 4.0L head eliminates the detonation problem that's common with the stock 4.2L-MPI combination. Check out Jaffer's page at http://www.monsterslayer.com/jeep for more info on the 4.0L -MPI combo.

Dean

I've been running my Jeep for over a year and a half. And I know people who ran the converison before I did it.

See my 4.0L Head Q&A on John Fontz's Web Page:

http://monsterslayer.com/jeep/40Head/40Head.htm

Tim Weaver
89-YJ 258MPI, 4.0L Head, Borla Header, Auto

I have the very same setup that I have been running close to three years now. It works great, I even use regular unleaded fuel without knocking. Contact HESCO, they were one of the pioneers for this conversion.

Enjoying Montana's Big Sky (& rocks & rivers & mountians etc, You get the picture.)

Oil

Ok I am in the prosess of doing a 4.0 head conversion to my gen#1 4.2
and noticed that if I fallow what seems to be everyones lead here I will end up with an oil free head!!!!! The 1974 258 is oiled through the rocker shaft ( it uses solid push rods. The 4.0 head is oiled through the push rods. So if one does not fabricate a spray bar how do the rockers get oiled? Am I missing something here?.....Boxcar...

Wow, old thread

The later 258's (mid to late 70's and later if I remember correctly) oiled through the push rods. I would think if you swaped to the later lifters and push rods with 4.0 or later 258 rocker arms you will be fine.

Welcome to the board!

You have an uncommon problem - there aren't many of those engines still around. Wilhelm is right. The easiest way around the problem is to replace the valve train. It's not a good idea to put new lifters on your old camshaft, though. There's a strong likelihood that new lifters will destroy an old camshaft, and vice versa. You should probably replace everything. Or build an external oiling system some way.