Rebuilding a 4.0

    • Rebuilding a 4.0

      Maybe rebuilding isn’t the right word but I picked up a 4.0 out of a 95 yj. It will be replacing the 4.2 in my 88
      My 4.2 runs so I’m in no rush. My plan is to pull the head and see how it looks inside, reseal everything, clean it up and maybe paint it
      What I’m looking for is any recommendations on upgrades/improvements/preventive maintenance while I have the motor out and am in no rush. I’m looking online and I’m pretty much overwhelmed with the information and opinions that are available
      Any input will be much appreciated. Thanks
      Matt
    • my advice is to do nothing. Its basically an old tech forklift motor. It works great if u leave it alone. If u were gonna reman i would put a slight cam and mustang injectors in but thats because its fresh.
      '88 YJ with not much '88 left. :)
      Team Mall Crawler #609
      Werock Stock Class we-rock.cc
      Werock '06 - 2nd East Coast, 5th overall Werock '07 - 3rd East Coast Sponsored by: The Drive Shaft Shop driveshaftshop.com Delaware Jeep Assoc. delawareja.com
    • astape wrote:

      my advice is to do nothing. Its basically an old tech forklift motor. It works great if u leave it alone. If u were gonna reman i would put a slight cam and mustang injectors in but thats because its fresh.
      Do nothing? That sounds easy! I have no plans of going into the bottom end unless it’s necessary. So far the only thing I plan on doing is converting to an electric fan. That’s not necessarily a “the motors on a stand so take care of it now” type of thing though, I’ll probably do that during the engine swap
    • the header isnt a bad thing because the factory manifold is most likely cracked. Intake and tb spacer and exhaust just make noise, imho.

      Clean it and spray a few cans of mopar blue or on it and call it a day.

      Also be careful with electric fans. They dont pull near as much air as stock when daily driving. There are many different cfm rated fans that look the same . Generally the price reflects this.
      '88 YJ with not much '88 left. :)
      Team Mall Crawler #609
      Werock Stock Class we-rock.cc
      Werock '06 - 2nd East Coast, 5th overall Werock '07 - 3rd East Coast Sponsored by: The Drive Shaft Shop driveshaftshop.com Delaware Jeep Assoc. delawareja.com
    • Well, I’ve gone further than I wanted. When replacing rear main seal I noticed the bearing was worn to copper. So I pulled another cap and another and another. All main and rod bearings are worn to copper. Local Napa recently closed their machine shop and I don’t like the other place that’s around so I ordered a reman crank and bearings from rock auto for $212. Cleaned the head, lapped valves and replaced seals... same machine shop I don’t care for said it was gonna be at least $350 for them to do that!
      Not sure why the bearings were so worn though. I was told the motor only had ~65k miles or something like that. I’m inclined to believe them too because it’s a reman.. pistons .040 over, bearings .010 under and after cleaning the block some I can tell it’s been painted gray maybe as if it’s a jasper
      Hopefully everything else goes smooth
    • could be a lot if things. Sometimes it doesnt mater how many miles r on it, but how it was driven. Low oil or never changing it will kill a crank?
      '88 YJ with not much '88 left. :)
      Team Mall Crawler #609
      Werock Stock Class we-rock.cc
      Werock '06 - 2nd East Coast, 5th overall Werock '07 - 3rd East Coast Sponsored by: The Drive Shaft Shop driveshaftshop.com Delaware Jeep Assoc. delawareja.com
    • Do I have to hone cylinders if I replace piston rings?
      I was talking to my dad yesterday and he said “I can’t believe you’re that far into the motor and you’re not gonna pull the pistons.” So I said fine, I’ll pull em. What he didn’t know is I already installed the new crank. What I didn’t know (it’s my first time doing this) is that it’s strongly recommended to hone the cylinders when replacing rings.
      where I’m at now is
      A) pull the crank and bearings, hone cylinders and replace rings
      B) replace rings and hope for the best
      C) just put the pistons back in
      Regarding option C as far as I know it’s a reman motor with 64k miles. I know a reman doesn’t mean everything was replaced but it’s bored .040 over so rings we’re obviously replaced. Also I cleaned the head and lapped the valves and the valves didn’t have excessive carbon which correct me if I’m wrong but I’m pretty sure is a good sign the motor didn’t smoke? So that would mean the rings are probably fine?
      I know option A is the safest bet but I’m kinda leaning towards C
      Thoughts?
    • You can buy a ball hone for a drill. As long as there is no major cylinder wear you can run the hone through to get a good crosshatch pattern on the cylinder walls. That will allow the rings to seat properly. It’s cheap insurance while it’s apart.
      2000 Sahara, All custom...
      2000 Cherokee Police package, Beater....

      I may be slowest and the stupidest
    • In my opinion if you replace the rings you need at least a hone. If you marked the pistons and can get them back exactly as they were then you could clean them and lube them and should get about the same compression as before if you're lucky. If there's any doubt about the piston locations then you're screwed, and need to hone.