Re: 4.0 Head on 4.2 Block?
I did this and had problems with it leaking, but what I later found out was that I should have done it my self instead of letting a mechanic friend of my dad's do it for me, which ruined the head I bought and I'm hoping that it didn't ruin the block because of the overheating that it caused. I was in college and didn't have the time to spend on modifying the head, etc... so the mechanic ended up half-way filling up the head with a block selant compound, even after I provided him with some liteature about how to pack a styrofoam peanut in there to keep it from happening and asked him to use quick steel. The guy didn't do either and ruined the head.
I ended up saving up and ordering a hesco head that had already had the waterports plugged up that needed to be plugged up. Then slowly I began to put it back together as time allowed. I got it in and the power was outstanding, but it still leaked near the back of the engine. After honing down the block to flatten the deck a little, I have gotten the head back on, this time using the spray copper to help the gasket stick. All I have to do is find time to put it in. I'm not in college anymore, but I got married last summer and haven't had much time after re-arranging my priorities.
I had a bad experience initially, but by my fault for not doing it my slef. I did all of the research and knew how it had to be done, but I let someone else do it and ended up with a problem.
Was the conversion, with the MPI worth it? I think so. For the brief time when I was able to drive it with the new head on it the power gain over the original 258 setup was amazing. And having the YJ sitting in the driveway for 2 years now has got me itching to get it done.... It shouldn't be more than a month before I get it all in and "driveable" again..
My only advice is to do more research than you could ever possibly need so you know what route you want to go. The mpi is good, but others have had success with a carb or the howell system on their jeeps.
Good luck with your conversion
4.2 w/<font color=blue>(4.0 head & MPI)</font color=blue>
After over 2yrs of driveway jeep'n, She's almost put back together.