• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Tips on Replacing My Engine

Hamzahng

NAXJA Forum User
Location
Dubai, UAE
Hello all,

I have a 98 XJ and the engine head was destroyed last weekend. I want to replace the engine with another one from the scrap yard.

I want to know what should I look for in the new engine, what should I expect and inspect, etc...

also, What do you guys recommend on what should I do when I get the new engine. for example flushing the engine, cleaning, etc... I have poor knowledge in this, so all your feedback will be appreciated.

-H
 
That is a big question! I'm sure there are lots of folks who think about it lots of different ways. Pulling an engine from a yard can be an undertaking. The 4.0 is pretty heavy!

First, are you sure you need an engine? Can you just get a head? Less risky (and cheaper and easier) if you know your bottom end is good.

Obviously, it is best if you can grab an engine that you know works. Otherwise, look for something with low miles (well, for an XJ!) that has been wrecked. If it was wrecked, that is probably why it is in the scrap yard. If it isn't wrecked, it is more likely to have mechanical problems.

I assume that your scrap yard won't have fluids in the engine. Otherwise, you'd look at them. If you have fluids and a battery, you can always check compression. But then you should be able to start it up too!

If it is dry, I'd pop the valve cover and oil pan. Look for no sludge up top, no metal in the oil pan. I suppose if you were picky you could also take some plastigauge and measure the clearance on a bearing or two.

My biggest recommendation is to do the freeze plugs on any engine you have out. They are cheap and easy. When the rear one goes, you need to pull either the engine or tranny to get to it. Get good brass ones.

Oil pan and valve cover gaskets, for sure. I'd change the rear main seal and put in a new oil pump, but only a good OEM quality piece (like a Melling--sticking with a high mileage stock pump might be a better bet than getting a cheapie). I bet your exhaust manifold is cracked. I'm having really good luck with the ATP stainless, for the money. I like the Spectra radiators for a mere $70. If you've got the original radiator, you are taking it out anyway.

Finally, take your time and read a lot. There are also many potential pit falls. For example, if you goof up torquing the rear main cap, you could destroy your new engine. If you aren't careful with a 500lb engine high up on a hoist, you could hurt yourself or a friend really badly. But, read up, have fun, and you'll learn a lot!

Paul
 
Whatever you do, don't flush the new motor. Best way to kill it if there is gunk in it. Just run synthetic oil or oil with detergent (like shell rotella) to slowly clean out any build up.

Personally before buying I'd look under the valve cover to see how gunked up or in what kind of shape the engine is in. (Oil pan too is you can)
These 4.0 are tough to kill so just about any motor as long as it was running will be ok, at least for short term.
If you've got the room to do it, a garage or work space, then a engine stand and replacing bearings and a few other things isn't a bad idea, sort of a refresh instead a rebuild . If not I'd probably pull the oil pan to clean it out and inspect it, depending on the miles which will probably be high, I'd replace the oil pump and of course refresh the seals and gaskets .

Pulling the engine get a good hoist and level work space. I alway work on cement, unfortunately my driveway has a slight incline and I've have had to work to slid the engine hoist with motor around to get it lined up or out of the way.
Now what I do is but a furniture moving dolly. Just a rectangle frame with four wheels that can take 1000 lbs, harbor freight has the for reasonable prices, then I bolt it to a wooden pallet to roll the new motor into place informer of the hoist and roll the old motor away.

Depending what room you have you can roll the jeep away then back in when you're ready, use a ratching strap to hold the transmission up where it should be if the crossmember is removed or pull engine and transmission at the same time .

Remember this is going to be damn heavy and unwieldy, 400 lbs easy then there's maneuvering the hoist, a friend to help isn't a bad idea but not a necessity. Still be good to have a extra pair of hands

You can use just about any XJ 4.0 ho motor from 91-99, ZJ and YJ up to I think 98. There will be slight differences but the motor is essentially the same.









Sent from my iPhone using Tapatalk
 
Look at the oil on the dipstick and under the valve cover cap. The oil should be clean and smell like oil. If its milky or watery, run away. If its black you need to look further, probably need to pull the valve cover to look for sludge, walk away if you find any.

Pull a spark plug and see if they are fouled. If they will let you put a compression gauge on it and crank the engine by hand, anything over 100 psi while cold and dry is good.

Assuming its clean, use some diesel oil with high ZDDP and some Marvel Mystery Oil for 500 miles then again for 3k, after that run whatever you want. Can get some GM Engine Oil Supplement (from a dealer) to bump the original break-in if you want.
 
Last edited:
buy from a junkyard that warranties replace anything broken if engine was pulled already transfer over your known good accessories (a lot of junkyards pull accessories) do a tune-up fresh fluids, valve ocver/ oil pan/ rear main/ oil filter adapter seals...and if you have never done this sort of thing definitely find some experienced help 4.0s are long and heavy and could end your life without experience


honestly probably something best left to a professional
 
I'd watch craigslist for awhile too -- I managed to find a motor in a 98 grand cherokee, still running , with 27,000 miles on it -- Little old lady owned, wrecked

It was at a shop and they pulled it once I bought it -- $350

Was my 1st swap -- I did it all myself, no issues just go slow

I did reseal everything but the head gasket -- Rear main seal was easy when the engine is on a stand -- also did new upgraded alternator, again fitting was easy out of the jeep -- New water pump, radiator and all freeze out plugs -- even with 27,000 miles I had on plug under the exhaust manifold that had a hole -- 2 others where really close

I did hose out the water jacket and clean any sludge -- there was very little -- I even did the threaded drain plugs

Just think it thru and take your time -- there is plenty of help right here on the forum if you have questions
 
Take the time to document your work as you pull the motor..lots of pictures. Will.help when putting evwrything back togather. Stay organized with the items removed. The lost bolts will be the one that will have to be chased down with a trip to hardware or parts store, or maybe junkyard.

Take the time to do the front transmission seal while everything is apart, along with verifying motormounts, CPS and anything else that is difficult to do with the engine in place.

Cleaning the engine bay and paint if so desired. Clean all grounds and electrical contacts of needed as you reassemble .

Above all have fun. If things are not going well, step back and enjoy a cold beverage of choice, or work on it later. The thrill of hearing the new (ish) engine fire up will be worth it
 
If you end up having to decide between a 98 ZJ block and another block know that there is no need for the oil filter adapter on the 98.
The 98 has the proper motor mount locations but has the newer YJ and WJ oil filter location.

Also note that the head on an 01 and 2000.5 have different sized exhaust ports. It will not work with your stock manifold. It also has a machining defect I dont feel like discussing now. Just avoid it... Casting is 0331.

When it comes to drivetrain hunting in U-pull-it yards, I look for the wrecked ones.
I think of it like this; they had to get to the accident somehow ;) Of course it's no guarantee. Just a best guess is all you can do other than what was mentioned above.

FWIW, I also recommend Craigslist unless you already plan on doing a full rebuild.
Normally you can hear it running or at least get the history on the engine.
And you can inspect it the same way you would at a yard.
 
Use paper bags for bolts -- write on the bag what is in them and the size wrench needed

I bought a package of 50 paper lunch bags -- maybe used 35 or 40 of them -- made it really easy to re-assemble knowing exactly what bolts where for what

Electric fan mount bolts -- 8mm
Alternator mount bolts -- 13mm
Air conditioner pump to mount bolts -- 15mm
Air conditioner bracket to block bolts -- 9/16

Anyway -- you get the picture -- all in separate bags -- And I was just guessing at sizes above
 
Back
Top