'84 2.5 to 2.8 interchange?'s

I have been trying to run searches to find my answers... But after scanning through about 50 pages of posts without an exact answer I figured I'd just ask directly. I have an old '84 xj with 2.5 and TF904 tranny, it has over 215,000 miles and the motor just doesn't have anymore to give. I can't find anyone interested in rebuilding it... So I am looking at possibly swapping in a 2.8 since they are so easy to find and affordable. My question is this: If I find an S-10 motor (carbureted or TBI) will I need an adaptor from motor to tranny?

Also, did the jeep 2.8 use a chevy bolt pattern on the bellhousing or AMC?

Thanks for helping out a greenhorn...

Ethan Rogers

Been there, built that. Now to answer your questions,
1) The 2.8 will DIRECTLY to the 2.5 bell housing. If you go auto, you willl need the correct flexplate/convertor set. For manual (preferred-go check prices for the t/c for the 2.8 torquflite tranny) the 2.8 is direct fit, but you will have to use the clutch plate for the donor tranny, not the motor. You will use the 2.8 flywheel and clutch cover, but the plate will be for which ever tranny you end up using.
2) The 2.8, 3.1, 3.4 and the 3.8 all use the 60* bellhousing pattern, just like the AMC 2.5. The FWD Caddy Northstar/Shortstar motors do too, but that is a WHOLE 'nother can of worms. The "Chevy" pattern is a 90* bell.

Concur. Having said that, you'd be better off getting a 3.1 or 3.4 (Rear Wheel Drive - the FWD version puts the starter on the wrong side of the block,) since the 2.8 is little more than a leaky boat anchor. The best way to rebuild one of those engines usually involved some cement and a length of chain...

You can find donors in the S-10/S-15, Camaro, Firebird, and the like. It doesn't hurt to check some FWD cars - a lot of "service" blocks had starter mount pads on both sides, and you should be able to see a starter pad on the back side of the FED block if it was a "service" block. I don't have the casting numbers handy, but www.60degreev6.com (?) might...

5-90

Frankly, the 2.5L Jeep 4-cyl is a far superior engine to the GM 2.8L V6. Either rebuild your 4-cyl, or swap to a 3.4L GM engine. Don't even think about putting in a 2.8L.

The 2.8L is simply not much of an upgrade power or torque wise so why bother?
It seems to me that, as soon as you go .60 over on the old 2.5L to true up the cylinders you'll be near 2.7L and have a fresh motor to boot.

If doing a 60deg upgrade is your bag, then consider a new 3.4L from GM Performance PN 12363230 HT 3.4 160hp, 194ftlb tq
Not sure why it says for carbs only though.

I really appreciate the help guys. I knew the 2.8 had a bad reputation but they are so easy to find. With what ya'll have said in mind I went to the little garage behind were I work and talked with the guy I knew there for awhile and he will rebuild it and even let me come over and help/learn. Nobody else wants to rebuild these little engines, he really didn't either but he will.

Thanks again,

Ethan Rogers

That should tell you something...

The V6-60 was a decent concept - but it didn't really get reliable until they came out with the 3100. I've owned both - I was always working on the 2.8 (mainly top end leaks - the valve cover gasket seals against the valve cover, cylinder head, and intake manifold. That point is great for starting leaks!) and it was underpowered from the factory. I traded that 85 Cavalier in for a 92 Corsica with the 3.1 - and I was actually almost impressed (I'm a truck guy - being truly impressed by a car is rare for me - and no, I'm not impressed by European cars, either...) I didn't spend anywhere near as much time working on that 3.1 as I did working on the 2.8, felt like it had about half again as much power as the 2.8, and the only trouble I had with that car was a girlfriend that liked to drive with both feet (she didn't know how to drive a stick - just one on the brake and one on the gas. I must have changed four wheels' worth of brakes on that car every 6-8 months! Not the car's fault, nor the fault of the design.)

The 3.1 and 3.4 are both far superior engines to the 2.8. Failing that, I'd consider something like a 305 swap using the AA bolt-in mount bracket, which would allow you to use either the THM350, THM400 (both 3-speeds) or the THM-700R4 (four-speed, reverse valve body) and associated transfer case - check with the FS Blazer or FS trucks for donors. Don't bother with a THM700R4 from behind a V6 - those damn things drive me nuts. I've had to rebuild entirely too many of them! They'll probably last a week or so behind a SB Chevvy.)

Just putting other options out there...

5-90

I wrote a big paper catalogging the notes I had gathered on swapping from a 2.5 to a 3.4, but it's in a word document so I might need to email it to you. Send an email to [email protected] and I'll reply back with it.
Jeep on!
--Pete

Save yourself a ton of hassle and get a 4 cyl from a newer Jeep (essentially the same bottom end till 2001, but the head and accessories are different) I helped a guy put a '94 YJ 2.5 in his '84 XJ, fuel injection and all.

Stick with the 2.5. It is a good little motor. I can find them pretty easy. Last one I got was just over $200.00. Get rid of all the stupid vac lines and adjust the timing and you should be good to go. I plan on rebuilding the original engine and throwing in some goodies, like a good Weber carb. I plan on staying with the carb. Everything on this engine is so easy. Any questions let me know.

Kim.