Motor swap ?

I have a 88 Comanche that has a beat, oil leaking, high milage(191K) stock 4.0 L. The rear main seal is shot(25miles per quart) and I think the head gasket is going out(no power). I was thinking that I should just wait til it dies and replace/rebuild the motor. On a scale of 1-10 how hard is it to remove and rebuild a 4.0L. I'm no mechanical genius but I have somewhat of an idea what im doing.(im only 17) Also how much does it cost for a decent rebuild kit.

I've never rebuilt an engine and I've been told that the 4.0 is a great one to learn on.

I'm 20 and I'm currently building a stroker. Until now the biggest thing i had done was bleed brakes and bolt in an intake. The tear down is SUPER easy, and if you are rebuilding it should not be to bad at all. putting it all back together... I'll let you know when i start.

All i can say is go for it, but realize that it will take you some time to learn. Its a good experiance and its a "cheap" engine to fix.

As for cost ummm... that i dont really know. If you need any internals let me know all my extra stroker stuff is for sale.

good luck
-Spaze

I much do you *think* the stroker is gonna cost you?

A 4.0 would be a good learner. The design hasn't really changed since the '60s. Get yourself a good repair manual and you shouldn't have too much trouble. I would STRONGLY suggest you build a stroker while you're at it, it will cost about the same and give you much better performance.

SO what makes you say the head gasket is blown. Do you have coolant in the oil?, blowing white smoke? If you want the rear main fixed so you can drive it without using so much oil you can do that without pulling the engine, as well as new rod and main bearings all while its in the truck. Just a thought if you can't/don't want to do a full rebuild just yet.

I thought that if you had a loss of power it could be the head gasket. I have had nothing but problems with this motor since i bought the truck 6 months ago.(replaced fuel pump, filter and gone through alot of oil. Also I want to rebuild it because it runs really bad(sputters stalls backfires and anything else that a motor can do wrong. I dont want to be driving down the road and have it break down on me. It would be nice to have a fresh motor w/ get a little more power. I knew that the rear main can be done in the truck bt i figured if im going to rebuild it i might as well just do it all when its out of the truck. I also have a month and a half til i can drive it on the road since i lost my license.(damn cops)

jeeppowermj said:

I thought that if you had a loss of power it could be the head gasket. Also I would like to rebuild it because it runs really bad. I dont want to be driving down the road and have it break down on me. It would be nice to have a fresh motor w/ get a little more power. I knew that the rear main can be done in the truck bt i figured if im going to rebuild it i might as well just do it all when its out of the truck. I also have a month and a half til i can drive it on the road since i lost my license.(damn cops)

Click to expand...

Perhaps you did something illegal?? It is not a hard engine to work on and everything is pretty straight foreward. Go for it, if you have problems we are here.

so far with a free engine $500 for the usual (crank, rods, bearings... even oil pump) $70 for new rocker arms and pivots (they were junked on the engine) $200 for new pistons and the cost for all the work (bore, balance, hone) is ~$600. Now, as for the head work, i dont know what I'm going to do there so maybe another $100 or so on that (porting and what not). I also need new injectors ($180) and I'm looking for another intake manifold, but the manifold can wait.

Putting it back together will take some time and other than getting it tuned back home so i pass emisions.

So far thats
500+70+200+600+100+180 an extra oh shit 300=

~$1950 for a 4.6L Then I'm going to try and sell the old 4.0 for $400-600

And that is a steal! I think it will be worth it. I'm learning a lot too.

good luck
-Spaze

Rebuilding a "stock" 4.0L is a piece of cake. Go get yourself the Jeep Factory Service Manual and read it, read it again, and then read it again one more time. Then go rebuild the motor as you are reading out of the FSM. I did the first rebuild on my 4.0L and it was easy. There is nothing major to screw up so long as you follow the directions. The only thing different I did was get a bigger "RV" cam that really helped out with the torque down low. I think it took me a 4 day weekend to build the motor and get it insalled and running.

The second 4.0L motor I built was a 4.6L stroker. The assymbly went the same as if I where building a stock motor. I had the motor built and running in less than 3 days over Thanksgiving weekend this past year. As for cost, do you have any preformance mods on the current motor like an intake, tbody, or header and exhaust? If you dont have any preformance mods like that, budget about $2,000 to build your stroker. Parts and machine work will cost around $1000 to $1200 and then another $800 for a header, intake, and injectors.

If you are in trouble with the cops and they revoked your license you WILL get in trouble again with the stroker motor :viking: My XJ on 32s will hold off a stock 5.0L mustang all the way through the 1/4mile and will surprise the sh*t out of anything up to 50mph or so because of the massive torque available off idle.

AARON

No I dont have any mods on it. How much did the first rebuild cost you, was it worth it, and where did you get your FSM.

Rebuilding the 4.0 is as easy as pie as long as you have a decent workshop manual to guide you (Haynes, Chilton's). I'd never built an engine in my life until I built my stroker last year. It was surprisingly easy for me because it's a mechanically simple engine that has fewer moving parts than any other configuration. Preparing the parts for assembly is the most time-consuming process but the assembly itself is quick.
__________________________________
Dino's "Mean Green Machine"
1992 XJ Laredo 4-dr - 4.6L I6 HO Stroker - 181k miles - AX15, NP231, D35c, D30

263hp@4900/321lbft@3300-3800, 1/4 mile = [email protected], 0-60 = 5.8secs
Websites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks

Whoa there now, let's not go crazy with all these thoughts of rebuilding. Leaking oil and poor performance (and even having 191k miles) do NOT necessarily mean a rebuild is needed, and a rebuild will NOT automatically give you a great running engine. "New engine" never automatically equals "reliable". My dad's brand new car left him stranded at work about a month after he got it because of a simple faulty sensor.
All sort of problems can cause the performance to fall off; clogged cat, failing trans (clutch or clutches depending on what type of tranny), poor spark, lack of fuel, a bad sensor, etc. There are TON of them that have *nothing* to do with the condition of the block. And if the actual problem isn't addressed, then that brand spanking new engine will suck just as bad and you'll be out a LOT of money in the process.
And I would never wait until an engine truly "dies" to get it rebuilt. In my experience, when an block ceases to turn, it generally means something VERY-VERY BAD just happened and that could greatly increase the rebuilding costs or completely negate using that block altogether.
I would start with getting a good shop manual ('89 Jeep factory manual preferably) and a multimeter and hit one item at a time to see if the parameters are within spec. A compression test is another good place to begin. And fix that rear main seal too. It's easy enough that you shouldn't wait because you "might" be removing the engine at a future date.
Rebuilding an engine can easily become a HUGE and EXPENSIVE pain in the butt (it's a 10 on my scale, I mean, how many of the normal repair tasks could be higher?), and more so if the problem all along was something stupid like a clogged cat. At the very least, invest in a junkyard block to work on so that the truck isn't stuck dissassembled and stationary if the project becomes overwhelming or you get distracted (life has a way of changing our priorities in a hurry).
Jeep on!
--Pete
ComancheClub.com

Pete, what would you recomend to replace before I tear out the motor. I know the normal stuff like sparkplugs, O2 sensor, spark plug wires, and air filter. I know its not a clogged cat because there isn't anything inside of it. Any other suggestions on things to replace would be great.

I'm certainly no mechanic (though I am the *only* person who touches my truck), I'm just saying that rebuilding should be the LAST option in my opinion. If your compression is good and the oil pressure is good and nothing is broken inside the engine, I can't see why it needs 1500+ dollars of work. My 190k+ 4.0L may be tired, but she still pulls my now-much-heavier-than-stock truck around with a surprising amount of authority considering what all she's been through.
I'd recommend starting a new thread stating that the engine is sluggish and see where that goes. Many of the others here can be of more help with where to start. But be as specific as you can with the description of the problems. "Da Jeep don't run right" probably won't garner much in the way of quality responses. :laugh3: Don't laugh, that happens fairly often. And don't forget that there's a ton of info in the archives. It might take a few trys to find the right combo of search words, but I'm sure you'll find tons of info.
Personally, I'd start with a compression test and see what that shows. It could provide a clue to what's wrong. Lots of the big auto parts stores will loan out tools like that for free. And get yourself a repair manual.
Jeep on!
--Pete
ComancheClub.com

P.S. have you changed the fuel filter? And what size tires do you have? Auto or manual tranny?

I changed the fuel filter and pump about 6 months ago. Im currently running 31" tires with an auto tranny. I want to put a 3-6" lift on it in the future and run 33" tires but that wont be for a while seeing as how im still in highschool.

Do you realize that taller tires will make the Jeep feel more sluggish? I put 30s on my manual tranny truck (back when it was 2wd) and it felt like an absolute slug all the time. Do you know of a couple of smaller tires on 5on4.5 rims that you could throw on the back and drive around the block a couple times? Do you know when the fluid was last changed in the tranny?
Jeep on!
--Pete

I bought the truck like 8 months ago so i dont know when the tranny fluid was changed last. Would that help? Also it just started to do this not too long ago and its had 31s on it the whole time i had it. Also i have a 2wd with 205/65 and damn is that thing quick, but it also has like an inch of ground clearance.lol

The automatic 4.0l XJ/MJs came with 3.55:1 so those 31" will add to the slug-factor.

Like Pete advised, I'd do some diagnostics and minor PM (IE compression, fuel pressure, sensor values) before I swapped or OH the motor.

If I found the engine tight... and it wasn't knocking, I'd fix that rear main leak, I'd also pop for a new-style 1pc rubber gasket and a new oil pump while I had the pan out of the way. If the motor mounts were toast, this would be time for new filter housing 0-rings too...

Swapping in a replacement motor is about a 4-5 on the PIA scale, depending on your conditions/facilities and how many extra hands you have. Some 10 minute steps can burn impossible hours trying to improv a second or third pair of hands.