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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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Nice thing about the old school chevy vehicles is that the engine mounting holes were basically already in the frames. Then swapping from one carb vehicle to another carb vehicle is pretty much making it fit. Then you just hook up the starter, distributor, fuel lines, and bam it's ready to fire since the entire exhaust would typically swap over without modification as well. Unfortunately, things aren't that simple these days. It's a bit more complicated than that with fuel pumps and wiring but in the end, it's a much better product. There are literally youtube video explaining, outlining, and completing the majority of the steps of 4.2 to 4.0 so you can physically see what has to happen. Unlike V8 swaps, the old 4.2 to 4.0 is a lot more straight forward....you just have to follow the procedure.
 

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I will point out that both of the motors you have located are OBD II which creates even more differences in what they have on them compared to what you have. OBD II began in 1996.

Dons suggestion of doing the full XJ swap is not a bad idea but IIRC the gauges on the OBD II XJ went to can bus comms to the cluster from the ECM. I am positive that the TJ in 97 was that way and have no reason to believe the XJ was any different.

There is no clear cut answer IMO and things little things like a cable or some wiring can create some serious roadblocks for some people. The actual swap may not be that bad, but the details may kick your butt.

There is no way for us to know your mechanical aptitude, what tools and shop equipment that you have, etc. Because you asked the question though it comes across as it may not be as easy for you as it is for others. There are a lot of variables. Yes. Swapping a SBC for another sized SBC or even going SBC to BBC was simple. It really is not a simple and straight forward as that in todays world.

There is no way for us to know how long it will take you. I can do things in an hour or two that take others a weekend, a week, even a month or a year because I do it everyday and have scads of tools and equipment and other resources at my disposal. You can put 10 experienced guys in one shop with the exact same resources and the speed that they will accomplish the same thing can vary greatly.

I am not by any means trying to discourage you but the fact that you posed the question along with the fact that you say it is confusing would make me think that you are going to go through a lot more 12 packs than you anticipate to get it done.
 

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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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Order a long block and , water pump, radiator, all hoses and gasket set. Also look into one of those minimum wiring efi kits and dump that carb. Your son will really like the idea of getting in jeep when its 100 or -20 and it crank right up. Or go with the 4.0 and deal with the couple days worth of wiring and have things you can get at any parts store.
Its not that hard and we can walk you thru it. Gauges are easy as swapping in a new better set as the ones in the jeep in there now are 34 years old. Also that trans maybe a crap one that is in it now. Look for a junked out 91 newer XJ with manual and you have a good set up
 

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When my kid's 88 was tired, I ordered a longblock 4.2 from... Autozone!
Go ahead and laugh but 4 years later it still runs perfect. And he was a 16 year old with a heavy foot. Autozone does not overhaul them, they sell them. And better yet, no shipping charge. Pick up and return to the store. They come in a nice heavy plastic clamshell.
It has good oil pressure. They used name brand parts. Autozone has a good warranty.
They load and unload. I had it in a few days from ordering. 5 year 50,000 mile warranty.
once broken in for grins I did a compression test. Everything was within spec. At the same time I got a new water pump and radiator and really flushed the heater core. I think I remember upgrading to a serpentine belt???
I had the trans (auto) rebuilt at the same time. I figured it should be good for 20 years.
Holley has a made for Jeep 258 easy install Sniper EFI kit too. That would be a great time to switch to FI. We put a Howell FI on his Jeep too. It's made from a Chevy 4.3. One of the best things you can do.. You'll love it.
 

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When my kid's 88 was tired, I ordered a longblock 4.2 from... Autozone!
Go ahead and laugh but 4 years later it still runs perfect. ...
I have an 89, some years back at 250K miles I replaced the engine with a Jasper rebuilt as well as Howell EFI. Definitely worth it. I'm over 370K right now
 
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Everybody who has suggested a 4.2 long block is really suggesting the easiet way to success. I will even add having a local reputable machine shop do a rebuild for you if you can verify from a good source that the machine shop is good, or you or somebody you know is knowledgeable enough to know if the machine work they did is up to par and do the rebuild yourself. I personally have not run into all these terrible machine shops that are supposedly out there in the world but have the blessing of dealing with many through work and get to see their work and its quality before I ever send them something of mine. LOL.

The Holley Sniper does have a BBD replacement system. It looks great on paper, I would love to lay hands on one. I believe that it most likely works well. The Howell system is proven. Many forum members swear by it. This has all been said but just re-emphasizing some good info.

Another place you can look at for EFI is affordable EFI. Some of their stuff is similar to the Howell because it is based off of the GM TBI systems.

Nothing wrong with sticking with the carb and it would be easy if you stick with the 4.2. Just pointing out that there are other options which may be easier than a 4.0 swap and a big reason people like that swap is they gain fuel injection.
 

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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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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
presumably a gasket would affect a single cylinder. So maybe cam timing. Recommend compression check.
 
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That's a drag (4 to 6 weeks) When we ordered the reman, I remember it taking from about Wednesday to the next Tuesday. I guess the supply chain is so screwed up.
Do a compression test. A little shot of starting fluid might be interesting. Put #1 TDC and make sure it's the compression stroke. Then check the timing marks.

Our local machine shops are awful so here that is out of the question. They are little mom & pop places than can not (or will not) absorb warranty claims. The money for claims literally comes out of their pocket. They'd rather lose a customer. They ruined a couple cylinders I dropped off (Yamaha Banshee) and screwed up a friends 454

It would be nice if you could somehow get by until you can get a reman. It's really peace of mind to know you've got essentially a new engine, broken in and maintained properly.
Our YJ's are permanent members of the family so I don't mind spending a bit extra.
 

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Our local machine shops are awful so here that is out of the question. They are little mom & pop places than can not (or will not) absorb warranty claims. The money for claims literally comes out of their pocket. They'd rather lose a customer. They ruined a couple cylinders I dropped off (Yamaha Banshee) and screwed up a friends 454
Years ago there were a lot of good local shops. They're largely gone as the old guys retired--rebuilding engines is not the business it once was. Of course there are some good shops, but they're rare and making good money building hot rods and racers.

I'd stick with the factory remans unless you KNOW someone local is really good.
 

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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
You are on the correct path. The firing order is 1-5-3-6-2-4 on the 4.2. So at TDC with your timing mark lined up to zero your rotor should point to #1 or to #6. There are two crank revolutions to one cam and distributor revolution so it will be at #1 on one revolution and #6 on the next revolution or vice versa.

The causes of what you have are a bad timing chain or gears which can include broken keyways or dowels that locate them to the component. The other is an apple cored cam and distributor gear or a broken distributor roll pin.

If it ran good and was quiet, you probably have an engine that is very repairable.
 

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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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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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You are on the correct path. The firing order is 1-5-3-6-2-4 on the 4.2. So at TDC with your timing mark lined up to zero your rotor should point to #1 or to #6. There are two crank revolutions to one cam and distributor revolution so it will be at #1 on one revolution and #6 on the next revolution or vice versa.

The causes of what you have are a bad timing chain or gears which can include broken keyways or dowels that locate them to the component. The other is an apple cored cam and distributor gear or a broken distributor roll pin.

If it ran good and was quiet, you probably have an engine that is very repairable.
Distributor gear roll pin. Yeah, I should have thought of that considering it happened to my Mustang. Drove me nuts for the day until I found it. Ford used a tiny roll pin. I drilled it out and used a much thicker Chevy roll pin. That tiny roll pin had to drive the distributor and the oil pump. I'm lucky I didn't loose the gear in the motor it was so loose.
 

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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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