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Welcome.  If you’ve found your way here, then you probably already have a cracked 0331 head in your jeep or you are thinking about a preemptive replacement of your 0331 in favor of the more reliable 0630 or 7120 heads.

I’m sure you are looking for some quick answers about this adapter plate, so let’s get right to it.

What EXACTLY does the adapter plate do?  It interfaces the older style heads (0630 or 7120) of the 4.0L engine to the stock exhaust and intake manifolds of jeeps that originally had an 0331 head.  This exhaust has two cast exhaust manifolds, two pre-cats and 4 oxygen sensors.

Why is it needed? The exhaust ports from the older heads are so much larger than 0331’s that if you install the older head (while keeping the stock exhaust) you’ll have a huge exhaust leak.  This plate blocks the holes. This sketch illustrates the problem. The other solution is to replace your manifolds, pre-cats and O2’s along with the head.

Will it fit my jeep? If your jeep originally had an 0331 head, you plan to keep your stock exhaust manifolds, and your planning to install an 0630 or 7120, then yes.  If you installed aftermarket headers for your 0331 before it cracked, then I’ll say probably.  If you want to try it out and see if it fits, then I’ll ship normally and accept a return if it doesn’t work out.  You pay shipping on the return trip though.

What else do I need?  You’ll need two exhaust/intake gaskets. Your stock 0331 gasket will be installed between the your stock exhaust and the adapter plate.  The second needs to be the gasket that would be installed with the 0630 or 7120 head your about to install and it seals the head to the plate.  Here’s the stack-up of the installed parts is. You’ll also need to find a way to support the ignition rail when using the older heads.  Because the older heads came from jeeps with spark plug wires, they lack the bosses to support the rail.  I made my own ignition rail brackets by bending up some 1″ wide x .090″ thick aluminum strips and drilling a couple holes to support the rail from the valve cover bolts.

Will it pass emissions inspections?  Mine passed no problem.  Because I have no idea of the possible other issues going on with anyone’s jeep but my own, I make no guarantees about this.  To date, no-one else has ever had a problem either though.

How do I buy one?  Go to the Purchasing Page.

For more info you, can read my full story here.  The long and short of it is this:  I designed this plate for myself so that I could swap my cracked 0331 head for an 0630 without replacing any of my stock exhaust components because I was concerned with passing emissions inspections.  I made some extras at the same time I made my own and put a post up on NAXJA (original post – 0331 to 0630 Swap Kit) so others could use it to fix their XJs (Cherokees).  People are now using it in any and all jeeps that have the 4.0L and are also using it with both the 0630 and the 7120 heads.

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