Phillip_C

Hey gents, so I finally got another XJ it’s a 1989. I have a slight knock that’s coming from what sounds like it’s coming from the bottom I just haven’t torn into it yet to check. I can find cheap 4.0 out of rigs getting parted out for like $100-$200. My question is would it be worth it to get one and tear it all the way down and clean everything and do all new gaskets then swap it in? The current one I’m looking at is from a 97 grand Cherokee. I’d like to stroke it but idk if I have the funds for that. So i was thinking just rebuild one then when I swap I could slowly gather the parts and stroke the other one?

How is hard is the rebuild? Cost to do it? What should I be looking for or ensuring I do when I do rebuild it?

Thanks for for all the help!

Mortgage Payer

I don't know why you would want to put the effort of tearing down an engine only to reassemble it as is.

The Jeep 4.0 is a simple straight forward engine that is a good choice for first time rebuilders.
There are a few books out there on rebuilding it. Start there.
The cost of the machine work can very greatly on who you use and whether you use Chinese or domestic parts makes a big difference too.

I bought a 1998 with a lower end knock that was otherwise in relatively pristine condition last fall.
It turned out the connecting rod bearings were shot and the mains scored from poor maintenance.
I'd exhaust every other possibility like flex plate bolts before assuming your engine's problem is what I had.

I paid my machine shop around $400 to boil the block, bore it .030 oversize, install new camshaft bearings, and grind the crank .010 under.
Around $750 bought me a parts kit from the top domestic names. I'm not new to this and did all the work myself over a few weekends.

Though I have not put many miles on it, I'm happy with the results.

Phillip_C

So you think just stroke this first one? I’m just unsure on what parts I need I guess? Or what it would cost.

DFlintstone

You might pull the inspection plate and make sure the torque converter bolts to the flex plate are tight. I hear they are known to loosen and cause a knock. Also one of my 90's has had a fairly throaty knock for the last 100K. I just got use to it. Was running fine AT 300K when I got rear-ended. Now it's a work truck "here on the farm", parked on the front lawn full of firewood at the moment.

I found my Utube on that >

sid06

m 95 has 380000miles on it and was gettin pretty noisy sounded like it was coming from the bottom end, I stuch a screw driver at the throtle body to hold the rpms at about 2000 rpm and slowly poured a couple quarts of water into the thotle body to clean the carbon out of the combustion chambers got rid of the knock may not work for you but doesnt cost anything to try

DFlintstone

Not a bad idea. I've never "de carboned" the one in that video. Forum, that really does work. Idk about "a couple of quarts", (never have done it), but a slow stream from maybe a detergent bottle will indeed remove carbon from the combustion cylinders, that could cause a knock.

sid06

I deliver mail so my Jeep runs 5 to 6 hours a day with a lot of that being idle time, I used about 20 oz of water the first time I did it and it quieted it down but still had a tick after warming up so I did it again a couple days later using more than twice the amount of water then took it out and run it hard for a couple of miles and that got rid of all the noise or ticking , I put a transmission in it about 50,000 miles ago and it started making a little noise as it got louder sounded like it was coming from the bottom end so i checked the converter bolts when that didnt make any difference and it seemed to be getting louder I was begening to think about a Reman engine.

dave1123

Just an observation from experience. Loose torque converter bolts will usually only rattle in neutral, but quiet in gear. Having said that, I bought a Chevy truck from a guy who had just replaced the engine and after about a week, it quit moving and rattled like a B****! He never fully tightened the bellhousing bolts and the flexplate center ripped out because of the misalignment.

Phillip_C

Well I checked the flex plate and everything looked good. Next stop is to ensure rockers are tight. Then I guess pulling pan and checking pistons and rings. Any other ideas?

sid06

I still say try decarbonizing its the easiest quickest and cheepest thing you can do and if it dosn't work you can still tear it apart, mine sounded like the one in the video

Phillip_C

Can you help me with how I decarbonize it? I poured sea foam in it while running them let it sit for 10 minutes then started it. I thought that was decarbonising it? I didn’t get any white smoke out the tail pip though. You way said to just pour water in the throttle body? Sounds dangerous lol sorry just give me a quick step by step and I’ll try it

sid06

I used a screwdriver to prop throttle open to around 2000 rpm then slowly poured water into the throttle body as the rpm's slowed I stopped pouring the water so not to drown the engine out and kill it let the engine catch up and continue untill I'd used about a quart of water , I did this with the engine at operating temp

Phillip_C

Is pouring water into the throttle body going to help more then when I poured seafoam into the throttle body? It seems like if that was the issue then the seafoam would have cleared it up? i will give it a shot but im just curious what the difference is. Thanks for the help!

PatHenry

Yes.

https://www.cherokeeforum.com/f2/cle...226313/index4/

https://www.cherokeeforum.com/f30/st...-4-0-a-226299/

Phillip_C

Well I ran about 30oz if water through the throttle body while at 2500rpm. No black smoke or any smoke at at all. Turned it off and put on the the air tube than ran it down the block. Cab smells a little but other than that i don’t notice anything different and I still have the darn tick/knock