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Unread 05-28-2012, 08:52 PM   #1
my91jeepyj
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1991 YJ Wrangler 
 
Join Date: Nov 2009
Location: st joseph mo
Posts: 41
YJ 4.0 Straight Six rebuild

I bought my 91' Jeep Sahara about 4 years ago and, unfortunately, the previous owners didn't take very good care of it. I had to rebuild the transmission in 09, followed by replacing the transfer case (which I got off of an XJ) and I knew it was only a matter of time before I had to rebuild the engine. This is a log of my engine rebuild effort.

To begin I had to remove the Transmission. I know most people say you don't have to, but it will make installing the engine a hell of a lot easier.
1.jpg


It's clear this engine has seen better days. I was getting a knocking sound coming from the rear of the engine. On top of that I was getting a lot of drive line vibrations, even after replacing the U-joints. I suspected the motor mounts.
2.jpg

I took the fan and radiator out and unhooked everything from the chassis. The only thing you really need to mark is the injector connections near the back of the engine. Everything can only go back into one place. It is a good idea to take a picture of all of the wire connections and all of the intake manifold connections before you take them apart!
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next pull it out
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Sure enough, as i suspected, a busted motor mount!
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After taking pictures, I took everything off of the engine. It was leaking oil from just about everywhere. Look at the build up of gunk all over. SMH
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I then took off the valve cover and oil pan. It's unbelievable how gunked up the head was.
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After taking the head off, I took out all the pistons and the crankshaft. It was a task knocking out a couple of those pistons. My cylinder walls were so worn down, it made a lip towards the top of the cylinder.
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The head and pistons. My goodness they are in bad shape.
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I took the block to the shop. Gary Didell helped me with the machine work. He bored it and honed it for me. Notice the ring around the top of the cylinders. The piston rings had worn deep groove into the walls. We had to bore it .060 over, and even had to sleeve the first cylinder.
10.jpg


Last edited by my91jeepyj; 05-28-2012 at 09:57 PM..
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Unread 05-28-2012, 09:39 PM   #2
my91jeepyj
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1991 YJ Wrangler 
 
Join Date: Nov 2009
Location: st joseph mo
Posts: 41
After boring it out, the cylinder walls were honed
11.jpg


New journal bearings are a must
12.jpg


After getting the crank turned to .010 over, it was time to lube it up and put it on.
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New pistons came with the kit. When attaching them to the connecting rods be sure the hole on the rod faces the cam side of the motor. That hole on the connecting rod squirts oil on the cam lubing it!
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It looks so clean
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Next the oil pump goes on and the gasket for the oil pan. A little aviation sealant along with silicon on the caps should ensure a good leak free pan.
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After a little paint, the head is put on. The valve job was also done by Gary Didell. I simply cleaned up the rocker arms and springs, no need to buy new ones. Be sure to mark which cylinder they go to before you take them off! Also make sure your push rods are clean inside and out.
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While torquing down the head one of the bolts broke. I had to go and buy a new set. Something you should keep in mind if you rebuild yours.
18.jpg


Now it's time to start putting everything back on.
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Unread 05-28-2012, 09:53 PM   #3
my91jeepyj
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1991 YJ Wrangler 
 
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Location: st joseph mo
Posts: 41
I replaced my pcv valve with an En-Valve . My old pcv must have given out some years back because I had oil all in my throttle body and air filter. The pcv fitting near the rear had clogged up causing the pressure to go through my front fitting which was used as a fresh air intake, instead it became a vacuum as the air going into my engine was pulling it in.
21.jpg

We had some problems starting it. First we had to prime the fuel rail by turning the key over just before engaging the starter, and then turning it off, waiting a few seconds and then repeating. When you turn your key over, just before starting it, it builds up pressure in your fuel rail for your injectors. After getting enough pressure it still wouldn't start. We then proceeded to check the timing. There is no adjustment for the distributor once you have it in, because the bolt holding it in place keeps you from advancing or retarding it. We took the bolt out and held it in by hand and turned the distributor until it started. Come to find out it was 1 tooth off. After putting it in the right place and bolting it down, it started up just fine and sounded great. Unfortunately for me I had to buy a new radiator because that one started leaking.
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Unread 05-29-2012, 08:52 PM   #4
blitz134
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1990 YJ Wrangler 
 
Join Date: Jul 2011
Location: Orange, CA
Posts: 219
Nice post!

What all parts did you end up replacing?

Any idea of the total price to do all of this?

I almost decided to pull and rebuild my 4.2 a couple of months back but decided it would be more than I wanted to pay at the time (although I ended up replacing most everything else, haha). But my bottom end still had good compression, even at 180k miles. So I decided to leave it.
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Unread 05-29-2012, 09:49 PM   #5
my91jeepyj
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I replaced almost all my sensors. The engine rebuild kit was around $430. The machine work cost me around $700. He cleaned it out, bored it, sleeved it, honed it, and machined the crank along with doing a valve job on the head and getting the gap right in it.

I spent a few hundred dollars on tools. Like a tranny jack and some jack stands, and a good torque wrench. The new sensors only cost me a little over $100. New crank sensor, temp sensors, map sensor. I bought new sensors for my throttle body, but I'm having a hard time unscrewing them from the body. I found a new radiator for it on ebay; all aluminum with two rows for only $165. A new oil pressure sender, new thermostat and housing, new hoses. I saved money by cleaning up the injectors instead of replacing them.
All together, having done the work myself, after cleaning material (shop towels and cleaners) and paint, I would say I spent close to $1900. (around $300 went for tools alone)

I decided against going with a new cold air intake system. I understand that it would need to be programmed if I changed the air flow. I tried to keep it stock. People are having too many problems when they stroke it, or put a bigger cam in it and such.

Overall, the straight six is a damn good engine. Even in as bad of shape as mine was in, it was still running. With 180k on yours, I would say it is due for a rebuild... rebuilding it yourself is much better than buying a stock rebuilt engine. I don't trust them, especially after opening mine up. It seems mine was "rebuilt" some time before I got it. I saw where they took short cuts, and rigged it up to save money. Half *** job means short engine life. Besides, nothing compares to the joy of fixing the damn thing yourself. For then, you know it's done right.

I took a look at your rebuild progress. You do good work man. Your head didn't look nearly as bad as mine did. I guess it all depends on how well you take care of it. I see you went with the Raptor bedliner; it came out clean. I was going to get that for my jeep, but I went ahead and got the Monstaliner. I plan on putting it in this weekend. You must have deep pockets with all the money your putting in that jeep man.

Last edited by my91jeepyj; 05-29-2012 at 10:03 PM..
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Unread 06-02-2012, 08:22 PM   #6
my91jeepyj
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Location: st joseph mo
Posts: 41
Well, I had coolant problems even with a new radiator. I finally figured it out though. See here http://www.jeepforum.com/forum/f12/9.../#post13662751
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Unread 06-02-2012, 11:15 PM   #7
blitz134
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1990 YJ Wrangler 
 
Join Date: Jul 2011
Location: Orange, CA
Posts: 219
Thanks for the compliments...I obviously try to do the best work I can and I want to do it right the first time. I think a lot of ppl have ongoing probs bc of shortcuts. I dont have too deep of pockets but i do admit that costs are adding up pretty quick. After my wheels and tires come in the costs should settle a bit since I wont feel I have any glaring reliability or safety issues.

The rebuild costs seem reasonable really. I considered getting a low mileage swap but its impossible to find for a 4.2 ( Im in CA so I didnt want to deal with a 4.0 swap just yet.)

Keep up the good work!
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