4.0 Rebuild Tricks

Hello, I'm 17 years old and have been four-wheeling with my Dad for almost all my life. I am competent in engine building as we drag race in the mud and on the strip. But most of my knowledge of engines is for big block Fords and Olds etc. And now it has come time to rebuild the motor in my '97 XJ. I was wondering what are some tips or tricks to building this motor for making more power. Here is what I was planning on: Lightweight and balanced rotating assembly, ported and polished heads, (done by myself), block bored .030 over (too much wear), shave down the heads, align hone the block, and a higher volume oil pump. I was wondering if there is anything else I should do while I have it tore down for durability and power, such as any oiling problems, casting lines that need to be shaved down, etc. This engine will see high RPM's occasionally and lots of high speed highway driving. Any help would be appreciated.

stroke it. Thats what i want to do, when i go to rebuild mine. A search under Dr. Dyno will yeild some good info.

I would like to but I don't really have the cash for that right now. Most of the stuff I listed is stuff that I can do or can get a great discount from some connections to have it done.

If you are already doing all of that, the difference in price for a stroker is a couple hundred bucks. You would simply swap the crank and rods($100). If you are boring, you need new pistons anyway. Normally in a rebuild you replace the cam, so upgrade the cam a touch and you are ready to fly.

So where would I get a crank and set of connecting rods for the same price of turning down and balancing a crank? Like I said I am getting a really good deal on all my machine work. So I need to get the cheapest prices I can. Considering I am still in high school.

you can get horses without increasing the stress on the engine, and your'e on the right track by thinking light.
I wouldnt shave the head or change the compression unless you want to be pumping premium fuel into her. Many high performance engines arent streetable, or daily drivers because they were too extreme. Stock blocks arent made to withstand 400 hp, though I think your 97 has the buttressed block.

Mild porting and polishing is safe for motor longevity, and may even up your mileage. But you need to be a robot to grind the exact amount off each port, or imbalanced flow can occur. If you go for the combustion chambers, you must shield the valve seats, or you could ruin them with one slip. Actually getting the CC's fully polished by hand is very laborious, no wonder ExtrudeHone has a business.

Generally, grinding away casting flash and radiusing sharp corners makes any part stronger, but again, you ought not grind on the rods or crank without some expertise. You would need to weigh and balance the rods if you took material away, and thats no garage job!

Headers rock! But they crack too. I'm still trying to figure which header is best, since ive seen cracking complaints from every manufacturer, and the el cheapo chinese manifolds give me the creeps. Im looking at an Omix-Ada 304 stainless header, it runs about $280.

Lightening up your valve train is safe, and aluminum rockers are affordable. There have to be better quality lifters available, stock lifters seem to be prone to bleeding down and getting noisy. If you change the lifters, youre starting a chain of replacement you should continue throughout the entire valve train, right down to the cam bearings. As a good rule, old parts should not mix with new, unless you can replace their bearings.

Adding a double-roller timing chain and new timing gears is wise, as is testing all your valve springs with a valve spring tester. If want to wind a 4.0 up to redline, you need tight timing.

My greatest suggestion is fasteners. They dont make an engine any faster, but they are great insurance for your motor. Invest in some quality high-strength headbolts, and in a digital torque wrench. Accurate torque is essential to completing your build.
Also make sure every bolt hole is clean and thread chased, and that will assure accurate torque readings.

Installing higher flow injectors is not great idea unless your increasing the amount of air the engine is intaking. Its a must for strokers, and waste for stock displacement.

Yea. You are right about upping the compression. I don't want to have to run premium (with gas the way it is) but i dont think that just shaving the heads down a little bit or just decking the block is gonna make that much of a change in compression. Also I am pretty experienced at porting heads. I know it is more of a science then anything but with the right tools and a good non-dgital caliper it can be done. I also know about the injectors and it isnt worth spending the dough unless you are seriously increasing compression.

You're right about shaving the head. Its safe to remove only enough to resurface it , and assure its dead flat.

A head as long as the 4.0 changes shape more when hot than a shorter eight-cylinder head, and it has cooling issues around cyl 3 and 4 because of the greater mass insulating it. A really shaved head warps more at operating temperature, creating sealing issues.

I worked on CAT diesel gensets, and they have 1 single head per cylinder. The block is one solid iron casting, with 12 sleeved cylinders. Just the crank weighs 1200 lbs! Even an engine this thickly built has peculiarites that arise when it reaches operating temperature. But its head bolts are arranged radially, and evenly around the cylinder, so the forces are equal. An auto engine would benefit from a design like this, but it wouldnt be cheap!

But the rule acrosss all engine sizes, it will seal better if its thick, even when hot.

An iron head, iron block jeep will last a lifetime if it never overheats.

The cost of stroking your motor just depends on how cheap you can get a crank and rods from a 4.2L Jeep motor. Something I noticed is on the front of the engine on top of the cam location theres a small opening that allows oil to leak down onto the timing chain. Theres a lot of casting edges around that opening that can be removed to help oil reach the timing chain. Also look between the lifter bored where the oil from the head drains back to the pan. A lot of thoes holes can be opened up so the oil can drain back down to the pan. Cleaning up the head will help out mileage greatly and even a home job makes a difference in power. There is nobody that makes a set of aftermarket head bolts for the 4.0L. The factory head bolts are 1/2" which is strong enough since you are not running super high compression. My stroker compression is around 9.6:1 and I have no problems with head gaskets or any other issues. I do run premium fuel, have bigger injectors, and an Apexi SAFC to control the injectors and fine tune the A/F ratio. A better radiator and 180° T-stat also help keep everything from overheating as well. Long as you keep it cool, it will be really hard do blow up.

AARON

http://jpmagazine.com/techarticles/engine/154_0508_insa/

This is a nice stroker build! They say its all it the heads, and its true!

The JP stroker got me interested. I was very much unimpressed that for over 3 grand Golen Machine couldn't have shortened the crank snout so it would work with serpentine belts. Crappy attention to detail in an otherwise great looking build.
Speedomotive gets $850 for their kit. Still a bit much to me. Gotta pay another 50 to have the crank shortened a bit for our application. Another $150 for balancing.
The path I plan to follow, should save a bit is this:

The crank, after the core charge is around $300, ready to go from Advance or Autozone, best of all you can order for a late application and get the 2.06 snout already on the crank. Comes with bearings.

The Speedpro hypereutectic pistons are about $22 apiece from Summit Racing. I can't find a reference to a price for the rings, can't be that bad and you have to buy the same ones either way.

If you can find a donor 258, especially the right year, you are way ahead I think, especially since you likely have a good relationship with a machinist if you are building drag motors. The machine shop I dealt with when I lived in Texas would give me killer prices on parts if he was doing the machine work. Yours might be able to score the parts cheaper, never hurts to ask.

Static balancing, if you own an accurate scale, isn't that hard to do at home. You might find something about it online, or I think the HP Books engine blueprinting book talks about it. Dynamic balancing (rotating) is a machine shop operation.

I am glad you are getting good responses. I recently asked about machine shops here in MI and got nothing. Apparently nobody in southern Michigan has ever rebuilt a 4.0 Jeep engine.

Incidentally if you do a search (read the sticky about searching) you will be overwhelmed with more info on the stroker buildup than you can shake a stick at. Us newbies gotta remember to use that. Then you can focus your questions to a narrower topic (such as reputable machine shops) that no one has read 25 times before and may or may not get an answer

Good Luck,
Randy

Randy_66 said:

I am glad you are getting good responses. I recently asked about machine shops here in MI and got nothing. Apparently nobody in southern Michigan has ever rebuilt a 4.0 Jeep engine.

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No, there are alot of poeple that rebuild 4.0's here, I think it's just that they all work at JTE (jeep truck engineering) and do it inhouse!

MrShoeBoy said:

The cost of stroking your motor just depends on how cheap you can get a crank and rods from a 4.2L Jeep motor. Something I noticed is on the front of the engine on top of the cam location theres a small opening that allows oil to leak down onto the timing chain. Theres a lot of casting edges around that opening that can be removed to help oil reach the timing chain. Also look between the lifter bored where the oil from the head drains back to the pan. A lot of thoes holes can be opened up so the oil can drain back down to the pan. Cleaning up the head will help out mileage greatly and even a home job makes a difference in power. There is nobody that makes a set of aftermarket head bolts for the 4.0L. The factory head bolts are 1/2" which is strong enough since you are not running super high compression. My stroker compression is around 9.6:1 and I have no problems with head gaskets or any other issues. I do run premium fuel, have bigger injectors, and an Apexi SAFC to control the injectors and fine tune the A/F ratio. A better radiator and 180° T-stat also help keep everything from overheating as well. Long as you keep it cool, it will be really hard do blow up.

AARON

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amc eagles also came with 4.2's and las time i saw one of them the entire car went for 50 bux.

warwagon98xj said:

amc eagles also came with 4.2's and las time i saw one of them the entire car went for 50 bux.

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Yup, I said Jeep just because its easier to relate to but any AMC 4.2L would work since Jeep was owned by AMC.

AARON

Hesco sells ARP head stud kits and main bearing cap stud kits.

Ok. Thanks for all the help guys but heres another question. Could I just get a new or reman. crank and set of rods for a 4.2 from a dealer (<---ripoffers?) or someplce like advanced or autozone. I know about using other engine parts from working with Ford's 351M/400. So all I would need is the crank and rods? Can use the original pistons? Also how do yall feel about roller rockers and cams for these engines? Is it worth it for sustained high RPM's? Appreciate everything. Now I've got to study Spanish. (Damn)

Hope I am not Hijacking this thread but if i am tell me to post another post.

I have a good 110,000 4.0 but would like to build a nice engine and having it readyt to swap in. I have two 4.2 258's Could I use that block to build a stroker 4.0 for my XJ?

258 block? Probably not - the walls won't handle being bored out to accommodate the 4.0 slugs.

The 258 has a factory bore of 3.750" (3-3/4",) while the 4.0/242 has a bore of 3.875" (3-7/8".) It's unlikely that the 258 block will have enough wall material to effectively survive the .125" overbore to bring it to the 242's bore (although it's possible, with ultrasonic checking. I've run across a couple 242 blocks that have enough material to take out to 4.000" and still have walls .100" thick!)

I suppose it would be possible to sleeve the 258 block - but it would probably end up being wet sleeves (coolant running directly against sleeves. "Dry" sleeves are pressed into an iron or aluminum bore without coolant contact.) However, sleeving the 258 block might be more trouble than its worth - see if you can find a 242/4.0 block and start with that. Use the 258 crank and rods to fit the 242 slugs with the longer stroke (or count counterweights - maybe I can use one...)

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