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Discussion Starter · #1 ·
Hey all,
I know there has been a lot, and I read a lot of the info out here on the forum on a 4.2 to 4.0 engine swap. It get confusing and overwhelming at times. just looking for some quick and clean answers.
I can't seem to find any decent 4.2's in my area to swap in my area but I have available two 4.0's , one is a 4.0 from 01 XJ that has been recently rebuilt and the other is a 4.0 for a 96 Grand Cherokee. Both have less then 60k on them. This is for my sons YJ and he is on leave and want to get it back running for him to take. Want to keep carb but also know most 4.0's do not have provisions for mechanical fuel pump. I know I will have to use 4.2 intake. Not sure about accessories.
I guess first question is will one the two engines work? and by work I mean changing engines in a few days or weekend.
In short, I want to use most of the parts off the 4.2 to get the 4.0 up and running... or do I need to look for a different year motor. Here is my baseline as simple swap.. as kids in we would take our 70's Nova's and Camaros and pull the 6 cylinder's on a Friday night and be out burning the tires off on Saturday night with 350's or 396's....

Thanks
Mark
 

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Discussion Starter · #5 ·
Thanks all and I agree about the EFI would be a superior to anything else. If I had the the vehicle’s that these engines came from And more then 12 days, I would probably install it. This is more of a time constraint to get running with the parts available, so from the conversation so far I’m going to assume that the 2 engines and not backwards compatible and I’ll have to look for some older ones.
thanks
 

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Discussion Starter · #11 ·
Thanks all for your input, I have checked into reman from Autozone here.. 4-6 weeks out and home delivery only.
The local machine shop about the same. So I'm focusing back on getting the 4.2 running that in it. It does have over 200k on it but was still running good. I was hoping you guys can give a little advice where to look. here is what its doing so far.. Son went to leave and it fired up , went to pull out , it coughed and shut off. Turns over but will not start.
Things I tried and checked.. Sparkplugs have spark, used starting fluid to try to start..it didn't even attempt to start.
Now here is the oddest thing.. I put my hand over carb to try to choke it and it has almost no suction and I mean very very little when turning over. This is my 2 best guesses it jumped timing or intake gasket. I pulled the distributor cap and rotated the engine with a wrench and went to 0 on the timing mark, now I rotated it once to 0 and then one more around to 0 and checked the closed the rotor pointed to was #3 cyl. What do you guys think?
Thanks
 

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Discussion Starter · #16 ·
Thanks.. Now it wasn’t quiet as a church mouse but not bad for 245k miles. I got a timing chain and gasket set. I’m going to pull it off today. I am going to do a quick compression test too before. I think if the intake gasket went it would still try to start. It turns over good just doesn’t fire up. Again it does have fuel and spark.
 

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Discussion Starter · #19 ·
If it is out of time due to the timing chain being off, it will not have normal compression readings. They usually have low readings across the board but there can be a cylinder or two that has unusually high or normal readings. This is because things are not moving in the proper sequence. (pistons and valves)
 

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Discussion Starter · #20 ·
Boojo35, thanks. I pulled the cover yesterday afternoon and it did jump. The sprockets/gears were worn down enough to let the chain jump. I appreciate the straight forward answers and help
I have a new gear set and cover ( funny Autozone had that). I did find a guy close to me that has a 258 for sale with 145k on it. I might pick that up and get that rebuilt in meantime I’ll let you know how it went after I get it back together. Little slow at getting it done since it been about 6 deg out. Thanks again
 
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