Engine 258 w/ cracked block... What Now?

[Bburkes419]

I have a 78 CJ5 AMC 258 i6 / 4.2l with a T-18 Transmission . I was getting ready to change out the exhaust manifold and discovered, under the manifold on the side of the engine block, a crack running from freeze plug to freeze plug. I have had this jeep for 4 years and put a ton into it. I couldn't figure out how I missed it. Well, it looks like it was covered with JB Weld, and it finally broke free. Under the shadow of the manifolds, the weld must have blended in with the block pretty well.

So, where to now? I have debated on trying to keep it as close to original as possible and getting a remanufactured 258. However, a buddy of mine has suggested finding an LS motor. Thoughts?

The LS would obviously have more power and could be quite fun. I am very much leaning in this direction. So, any advice, things to watch for, things to watch out for would be appreciated.

Thanks,
Brett

 

[Manic Mechanic]

Unless you can do the work yourself and you know the motor doesn't need rebuilt you can easily get 20k deep in this swap. You will definitely need a new Transmission , drive shafts and fuel system. Possibly axles as well.

Cheapest fastest way would be a replacement AMC 258 i6 / 4.2l even a used one that needs rebuilt would get back on the road faster and vastly more affordable than an LS swap

 

[Apple]

I would look into fixing the crack if it is the only one or find a replacement short block and rebuild the head and put it back together.

 

[hole]

OP, how do you intend to use your 5? Do you live where vehicle or emmissions are inspected/tested? Are any fluids leaking at the crack, or could it be a casting line? If its been there for 4 years and has not been a problem, you could keep driving it until it is one. The more information we get, the better advice you will likely get.

 

[TSB8C]

A replacement short block would be cheapest and quickest. If you were happy with performance and other factors with what you had, just stick with that. But if you've been dreaming of an upgrade for more power, better cold starts, and reliability, now you have the perfect excuse to pull the trigger. Your T-18 can be mated to a GM engine like a SBC or LS, and can also handle the power output if your engine choice isn't too wild. But like Manic said, be prepared to open your wallet. I swapped my AMC 258 i6 / 4.2l for a fuel injected SBC and wouldn't ever go back - and my 258 was running fine. I just wanted more power and reliability.


GM engine swap will require the engine, lots of wiring changes (if fuel injected), adaptor for Transmission , engine mounts (I made mine from scrap metal), potentially new drive shafts due to changes in lengths, and different radiator and hoses. Fuel injection will require electronic fuel pump, regulator, and new hoses. Different exhaust manifolds or headers. All the "fun" you can imagine.

I did my full swap for around $15K. That included a brand new Crate engine (not a rebuild) that included the wiring harness and ECM, headers, mufflers, and new dual exhaust, rebuilt 700R4 transmission (also swapped out the T-150 ), torque converter, Novak adaptor for the Transfer Case , homemade engine mounts, new radiator, new drive shafts, Lokar shifter, twin-stick kit, new tunnel cover and boots for the shifters, electric fuel pump, fuel pressure regulator, misc. hoses/connectors, and lots and lots of marrying the wiring into the CJ's harnesses. Did mine about 5 years ago during Covid shutdowns (lots of free time). Probably more expensive now.

 

[Belizean]

It all adds up fast. I went from AMC 150 to AMC 258 i6 / 4.2l during that time also.

 

[Ernie]

I just about to get my 1985 jeep CJ7 back from the mechanic. He has been working on it for 4 years now. I had it swapped onto a 1996 Toyota 4Runner. So now my whole drive train is Toyota. 3.4 automatic 4x4 e-locker
A/c heat all work from the 4runner. He just painted it and getting it all put back together. I even used the 4runner original gas tank I had to have it cut down 10-14 inches so I’m down to like 10 gallon tank.

 

[Manic Mechanic]

Skys the limit. Your budget and skill level as well as tools and place to work is the hold back

 

[letsgobrandon]

A stroker is 10k. Id do a crate AMC 258 i6 / 4.2l and be done with it. But first: go till it blows,you have nothing to lose here.

 

[cinaed]

The old tried and true AMC 258 i6 / 4.2l block is legendary, and despite that crack she is not done. I know because I was travelling at speed on the Georgia 400 North of Atlanta in my old Cherokee (SJ) powered by a 258, and she broke a connecting rod clean in half and the bottom half punched a fist sized hole in the side of the block. The vehicle puffed a large plume of smoke, but it was all good as the other driver's gave me some room, and I was, amazingly, able to remain under power for a few miles till I found my favorite Tire Center where I was able to recover from the excitement.

I should have kept the block and fixed it. It could certainly have been repaired, I could have welded in a patch and replaced the piston and connecting rod, but another engine became available so that was the route I chose. So if you must, and want to keep that engine, she's not done. Weld that crack if you are competent to do that yourself, or get someone who can do it in a competent and professional manner for the type of metal in that cast iron block.

 

[Manic Mechanic]

I broke my #1 piston in half and had a hole in the #2 piston and was still rolling up the highway at 65mph

 

[Jeep Soup]

Here is my Nickel.95......
All is Not Lost on a Cracked Block. With Modern Welding Techniques, it can be Welded at a Welding Shop! You will have to Remove the Engine and get a Working Area by the Crack for them
You already have the Manifold Off.
Call around. I have had Vintage Intake Manifolds, Blocks, and Heads repaired way less than A Whole new Short Block.

 

[TSB8C]

LS engine swap. Now you have an excuse.

 

[Jeep Soup]

LS engine swap. Now you have an excuse.

HA.....
Some People's Children !!
Low Speed Torque Is King in Mountian-ing.
That Torque Curve on a Inline Six is Perfect, and you don't have to Ride the Clutch. Pick your gear,
Wave as you Creep By all those
"High Dollar, High Rise" rigs looking for a Winch out......