thejim42 Posted November 15, 2014 Share Posted November 15, 2014 Looking at my options for motors for my mj. I think my 4.0 is a bad rebuild and was wondering if a 4.2 from an 89 yj would swap in? My buddy has one that I can get fairly cheap. Any ideas what it would take? I know at least the intake to go to fuel injection from carbed Link to comment Share on other sites More sharing options...
FrankTheDog Posted November 15, 2014 Share Posted November 15, 2014 You can get good used 4.0's for a few hundred bucks a 4.2 is a big step back. I just drove home a 1992 with 74k on it for $300. Body is wrecked on one side, it was Tboned but still drove good. They are out there, you just have to let everybody know that your always looking. That's how I get them. Link to comment Share on other sites More sharing options...
dankicksass Posted November 15, 2014 Share Posted November 15, 2014 Take the crank and rods from the 4.2 and throw the rest away. Instant stroker kit. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted November 15, 2014 Share Posted November 15, 2014 Take the crank and rods from the 4.2 and throw the rest away. Instant stroker kit. Yaaaa boyy. But seriously, 4.0s are plentiful and most of the time cheap. I pulled mine straight from a JY ZJ with something like 130k. It's still going strong 20k later. Paid something like 250 for it. Link to comment Share on other sites More sharing options...
Eagle Posted November 15, 2014 Share Posted November 15, 2014 Looking at my options for motors for my mj. I think my 4.0 is a bad rebuild and was wondering if a 4.2 from an 89 yj would swap in? My buddy has one that I can get fairly cheap. Any ideas what it would take? I know at least the intake to go to fuel injection from carbed You "think" your 4.0L is a bad rebuild? Wouldn't it be wise to be certain before you go through the exercise of an engine swap? What makes you "think" your engine is a bad rebuild? Link to comment Share on other sites More sharing options...
thejim42 Posted November 15, 2014 Author Share Posted November 15, 2014 I have 80psi of oil pressure, when I step on the gas I hear a rattle. It misses at idle it has low compression and burns a rediculous amount of oil and when I changed my oil I had a metallic shimmer in it like there was metal in it. The only reason I'm asking about the 4.2 is because I can get from my buddy for nothing. I plan on pulling the motor anyway to do my 4x4 swap and paint Link to comment Share on other sites More sharing options...
FrankTheDog Posted November 15, 2014 Share Posted November 15, 2014 I guess that's one benefit of living in the rust belt. Drive trains are cheap. Link to comment Share on other sites More sharing options...
benjy_26 Posted November 22, 2014 Share Posted November 22, 2014 I've heard that using a HO head on a 4.2 is something the CJ guys do for a power boost. I wonder how a 4.2 with the 4.0HO head and FI system would work in one of our trucks... Link to comment Share on other sites More sharing options...
Eagle Posted November 22, 2014 Share Posted November 22, 2014 I've heard that using a HO head on a 4.2 is something the CJ guys do for a power boost. I wonder how a 4.2 with the 4.0HO head and FI system would work in one of our trucks... It does okay. In fact, Hesco sells (or used to sell, as did Jeep) a conversion kit for that exact purpose. A friend of mine installed one in/on a YJ several years ago for a customer. Overall, you get an improvement over the stock 4.2L but it still won't be a 4.0L. The 4.2L has a longer stroke but a smaller bore. Long-stroke engines are good for torque but they don't particularly like to rev. Link to comment Share on other sites More sharing options...
yxmj Posted November 22, 2014 Share Posted November 22, 2014 Take the crank and rods from the 4.2 and throw the rest away. Instant stroker kit. X3 :thumbsup: Link to comment Share on other sites More sharing options...
benjy_26 Posted November 22, 2014 Share Posted November 22, 2014 I've heard that using a HO head on a 4.2 is something the CJ guys do for a power boost. I wonder how a 4.2 with the 4.0HO head and FI system would work in one of our trucks... It does okay. In fact, Hesco sells (or used to sell, as did Jeep) a conversion kit for that exact purpose. A friend of mine installed one in/on a YJ several years ago for a customer. Overall, you get an improvement over the stock 4.2L but it still won't be a 4.0L. The 4.2L has a longer stroke but a smaller bore. Long-stroke engines are good for torque but they don't particularly like to rev. Damn. I thought I had found a sneaky way of making a REALLY low buck stroker! :) Link to comment Share on other sites More sharing options...
thejim42 Posted January 30, 2015 Author Share Posted January 30, 2015 its been a while but i ended up figuring out my issue is just valve seals. 650 mile trip at 75-80mph for 10 hours and didnt burn a drop of oil and it only burns when i first start the truck and its cold. Link to comment Share on other sites More sharing options...
Eagle Posted January 30, 2015 Share Posted January 30, 2015 It's always nice to know you don't have to swap out the engine ... Link to comment Share on other sites More sharing options...
cruiser54 Posted January 30, 2015 Share Posted January 30, 2015 its been a while but i ended up figuring out my issue is just valve seals. 650 mile trip at 75-80mph for 10 hours and didnt burn a drop of oil and it only burns when i first start the truck and its cold. What about the metal shavings? Oil pressure? Link to comment Share on other sites More sharing options...
thejim42 Posted February 12, 2015 Author Share Posted February 12, 2015 the shimmer turned out to be my zinc additive a when the motor was rebuilt a high volume pump was put in. it only hit 80 psi when it was less than 20 degrees outside but at normal operating temp it runs between 40 and 60 psi. Link to comment Share on other sites More sharing options...
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