hey ya'll i'm looking at mabey a cracked head or at lease a new head gasket the motor already has a rod knock so now im thinking just rebuild and modify a 4.0L i've heard that any year/model jeep 4.0L but the post 97 motors are the best is that true? if not what motor should i be looking for? im looking to put in a bigger cam do some port work and get a '99 intake for it i dont wanna do a stroker or anything like that just build a stout strong running BUDGET (lol) motor

p.s. im also looking at a 5 speed swap

 

97-99 were good years for motors. 2000 and up ChryCo switched to a different casting for the head (0331 Casting) and it is prone to cracking, so beware.

 

When I bought my XJ I thought it had a severe rod knock...turned out to be torque converter bolts were loose...but while I was thinking and studying on it, I decided the best route was a used motor from craigslist. There are always xj's being parted out. Grabbing a motor for a few hundred bucks was, in my thinking, the easiest path. My research on rebuilding was that it cost between $1400 (for a long block from a rebuilder) to $2000 for a do-it-yourself rebuild using local machine shop support and high-quality parts. For that kind of money, you can buy four or five used engines.

If you can find an engine that you can hear run, you can "leakdown" test it. That will tell you a TON about it's condition in a matter of thirty minutes. All you need is a leakdown tester ($50 tool from Aircraft Tool Supply in Lansing, MI) and a portable compressor or air tank. I know it sounds like a lot of fuss...but the cost of long blocks and the uncertainty of the quality of the rebuild work makes a leakdown test on a used engine seem sensible to me. If these were ordinary engines, I would not bother, but these 4.0 motors can run 300,000 miles if given reasonable care. I just spotted one in Detroit with 152k on it for $300...and it's in the car and running. Hard to beat that.

Just my two cents...

 

i've had people tell me that its the oil pump making that noise (a co-worker he is a truck driver not a mechanic btw) also the kid i bought it from said it was a lifter tap ill check out the torque converter bolts though...but im sure that its a rod knock i've had my fair share of them lol also the truck is backfiring through the intake i checked the code wrote down the number of times the light blinked now to research what the numbers mean i might be able to skate by for just a bit longer till i need it so i can build the new motor w/ the trans swap with more money

 

Really '91 up is good, since they are the HO. The 97+ motors have more webbing in the block making them stronger, but I've yet to hear of someone with a pre-97 block that failed who said, "Wow, if only I'd had more webbing in my block!". Usually blocks fail because they get a new window in them, I don't think webbing would make a difference there.

Avoid the 00-01 heads if you can.

 

A++ answer. I've always thought the same...never heard anyone say "geez, I wish I had more webbing". Great answer.

 

so i can use other heads besides a 91 head? this may be a dumb question i know on fords you can (302 to 302 ext.) but really know nothing about jeeps or efi im still going to be looking for a '99 motor for the intake and other parts that id need for that conversion, but if i could use that head as well that would be nice

 

91-01 head should fit on any 91-01 engine block, the engines are practically identical.

 

-Spiderman

 

What a random comment on such an old thread haha.

 

:-) I found this thread researching a 97 head into an 01. thought I would post something since its so old

 

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