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  • TJ: engine rebuild results

    132,000 miles on the 97 TJ 4.0. Low miles if it were highway miles but there are plenty of wheeling miles on it as well.
    Over the past couple of yrs (and only a few thousand miles in those yrs) I've developed a progressively stronger tick/rattle/knock..... Initially it was at a cold start up and I attributed it to piston slap which is pretty common. It got worse. I noticed that my hill climbs on the freeway turned my jeep into a uhaul truck in the slow lane and I could hear what I thought was a exhaust leak so I replaced the manifold with a JBA header. #5 exhaust was in fact cracked but not severely. Not to mention it didn't help the noise, or performance..
    Soon after the knock started to turn into an inconsistent sound which sounded more like a rod knock instead of piston slap or injectors. I figured I didn't want to throw any money at diagnostics/mechanics to do band aid repairs and since she's nearly 20 yrs old I decided to just get a rebuild.
    I thought about a stroker for some time now and did heavy research. Actually built a 4.6 a few yrs ago when the noise 1st developed but chickened out due to a lack of confidence being my 1st build and sold it for what I put into it minus time for sourcing parts, driving to the machine shop etc.. (PITA!)
    I've read that MANY strokers fail at less than 20,000 miles and I don't want to be a statistic to that fact. I'm not a desert KOH racer and I prefer to drive slow on the trail. I just wanted more highway zest remembering how she was when I first bought her. A rebuild is in the 1500.00 price range while a stroker is about 4000 aftermarket and around 2300 built yourself. With the extra money I'll throw an Atlas at it figuring gearing is equally as important if not more than hp/tq on the trail.
    Anyways, I opted for a rebuild. It's getting bored 0.030 over, new everything except the crank which is getting reconditioned for 1625 after taxes.. Drop off and picked up long block. I called the shop yesterday to see how it was coming along and what if anything did they find. The found a cracked piston skirt, with the cylinder wall scratched up and 2 worn cam lobes. I guess my OCD was legit. I'm glad I took it in when I did because I do a lot of desert gold prospecting and wouldn't want to be stranded somewhere with a thrown rod or busted piston...
    I googled "jeep cracked/broken piston skirt" and was rather amazed that it's a pretty common issue from 95-2000 4.0's. Why? No idea but if you start to develop an obvious rattle, knock, piston slap type sound at cold start up and it seems more than your "normal" characteristic you might wanna get it checked out. Just say'n.
    Last edited by brokenujoint; 02-25-15, 11:18 AM.
    1st batch TJ bought August of 96. Locked and Loaded!

  • #2
    There was a stroke change in 96 supposedly to improve harmonics. It effectively reduced the CID by 1 - from 242 to 241. It would be interesting to see if it affected the position and timing of the throws on the crank. Glad you caught it before it caught you.
    God forgives, rocks don't
    -sons of thunder

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    • #3
      picked it up from the shop today. Didn't have much time other than to unload it and get it on the engine stand and tuck it in the garage til this wknd.
      1st batch TJ bought August of 96. Locked and Loaded!

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      • #4
        I wonder if folks have put a mild cam in some of these motors, get a bit more power out of them? Seems like that might be safer on the life of the motor than a stroker crank would? Probably wouldn't make as much power though.
        [COLOR="#FF0000"]R[/COLOR]edneck [COLOR="#FF0000"]D[/COLOR]riveway [COLOR="#FF0000"]F[/COLOR]ab
        www.DanielBuck.net - www.DNSFAIL.com - www.FurnitureByBuck.com

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        • #5
          Originally posted by daniel_buck View Post
          I wonder if folks have put a mild cam in some of these motors, get a bit more power out of them? Seems like that might be safer on the life of the motor than a stroker crank would? Probably wouldn't make as much power though.
          I tried getting the shop to put in a mild performance cam instead of the oem. They wouldn't budge. Well, they said they would but that it wouldn't validate their warranty which for me, since I'm doing the long block install is 2 yr 24,000 mi. Rather priceless compared to the mild gains of a mild cam. I shaved about 300 lbs of weight from the jeep with Savvy stuff and general jeep dieting. That alone helps out a lot.
          1st batch TJ bought August of 96. Locked and Loaded!

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          • #6
            Adding the aw4 will rob you some power over the manual trans though.

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            • #7
              Yeah, I'm aware of the 30% parasitic draw that it takes but I also see how smooth and sweet it appears on the trail when guys use an auto over a stick.
              Side note: All done and just waiting for some free time to get it back in the jeep.
              1st batch TJ bought August of 96. Locked and Loaded!

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              • #8
                Update: Engine runs like a champ. Only issue is a a rear main seal leak. At first it was bad. Like 8 drops overnight bad, but now it's very minimal. It still bothers me though and will probably change it out at the next oil change. MJM machine in Escondido did a great job. Bone stock rebuild bored 0.030 over. Now instead of driving up the 15 from the 215 into San Diego I don't have to be in 4th gear in the slow lane limping at 55. I am in 5th in any lane I want and can go beyond 70 if I choose. Also my mpg has gone from 14 to almost 17.

                Other than pipe-dreaming that I went with a V8 I can't complain.
                1st batch TJ bought August of 96. Locked and Loaded!

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