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Old 12-02-2016, 03:36 PM
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CessPooL's Avatar
Join Date: Dec 2016
Posts: 73
Jeep Noob - 90 YJ w/4.2

Hello all.

I'm new to the jeep thing. I do own a 46 CJ but its some sort of a project I got from my grandfather when he passed years ago. I've never really been into jeeps too much, but with that said, I just bought a 90 YJ. 4.2 carbureted with AX15 trans. I have been looking on forums as of late and searched but don't seem to have any real luck with what i want. if its out there (and I'm sure it is) my apologies for the post, but i don't spend too much time in general online anyway...

My daughter has wanted a jeep for awhile now, her boyfriend has one and i've been beaten into submission finally... This will be a christmas gift for her. The frame and body is solid, but it does have its fair share of issues. One being the syncros are going out in the trans i'm told. I don't feel any issues with driving it, and ill have to look into it more once I can get it out of hiding. But for 3k and being this clean, I was more than happy.

As stated, it has the 4.2. He has a new carb and electronic choke and it has no issues starting in cold. I guess the 4.2 is less desirable than the 4.0 and if I have to pull the trans to rebuild it i'm going to overhaul the engine as well. Really, my biggest qualm with the entire jeep is how dirty the engine bay is. Id love to pull everything and clean it up. With it out id like to look into putting the jeep MPI kit on it (I know, pricey) and with that it says the engine should be relatively fresh I'm seeing. Well if I have to overhaul the engine, might as well bore & stoke it a bit eh?

Really, what I want is a nice procedure / guideline for tearing down one of these engine start to finish to read over. Not just "use these rods and that piston with the 4.0 head." etc etc with that said, what is the safest bore if you will? not for crazy power, but more for reliability over anything. can the 4.2 be stroked also? More torque would be nice for her (as i'm teaching her to drive a manual on this) and what would or would not work with the MPI kit? I don't care to put a 4.0 head on it and go to higher octane gas as long it doesn't compromise anything else or interfere with the MPI.

So is there a guide out there for a tear down / rebuild? And whats the right direction for a mild stroke & Bore with reliability on the forefront?

Also, are there roller cams made for the 4.2? I will build it up mildly i'm sure when the time comes.

I figure I will let her drive it around this summer and then make the rebuild a winter project. Id like to buy everything i need over the next several months and be ready when winter comes.

Thanks all!!

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Old 12-12-2016, 11:44 AM   #2
WhoIsTJ's Avatar
Join Date: Nov 2016
Location: Ontario, Canada
Posts: 12
Jeep looks like it's in really nice shape! She will enjoy it!

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Old 12-15-2016, 12:08 PM   #3
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Join Date: Apr 2005
Location: Smethport, PA
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In my opinion, it is not worth all that time and money to build the 4.2. For less money you could get a low mileage 5.3 V8 and stick it in there. The 5.3 swap is so common there are plenty of conversion parts and information available.

It looks like a real nice Jeep. I am sure it will make your daughter happy.
87 YJ, 5.7/TH350/NP241, Custom 4 link/ Radius Arms, ADS Nitrogen Shocks, 35" Cooper STT
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Old 12-15-2016, 05:45 PM   #4
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Join Date: Apr 2013
Location: Highland, California
Posts: 2,289
Look into building a 4.7l stroker instead of "building" a 4.2l. You basically put the 4.2l crankshaft into a 4.0l block and bango, instant horse power. Probably cheaper overall than doing an engine swap or such since it is bolt in.
Build Thread 1989 YJ, Chevy 355 TBI, 700r4, np231 sye/wide chain/6 pinion planetary, D30/8.8/4.56, 33" A/T's, bds 3.5" springs, 1" Boom Shackles, crossover heim steering
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