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 AMC 258 i6 / 4.2l . 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 AMC 258 i6 / 4.2l 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.