YJ frame under a CJ

PhattyX · #1 (**permalink**) 01-04-2008, 04:04 PM

Sadly, I've found a pretty decent size crack and rot in the frame by the motor mount. One of the options I'm considering is getting a new frame, adding a lift and replacing the axles, then putting my tub engine and trans/transfer case on it. The question is, can I use a YJ frame to replace my '84 CJ frame? I have a 360 in it, but I think that's negligible.

I know the front YJ springs were wider. Would the lift springs for a YJ be wider/better than lift springs for a CJ?

Also, the YJ frame I'm looking at says it will not work with a 4cyl, just the 6cyl. Does anyone know what the difference is or were they really the same?

Thanks, as always,

-X

Junkpile · #2 (**permalink**) 01-04-2008, 04:23 PM

You need the 6 cylinder version since you plan to put a V8 in it. The engine mounts are different between the 4 and 6, but an AMC V8 will drop in place of an AMC inline 6. So putting your 304 in a 6 cylinder YJ frame is easy.

The reason the wider spring is better is because it doesn't have to be as stiff to carry the same load. YJ front springs ride much better than the narrower CJ front springs.

PS89YJ · #3 (**permalink**) 01-04-2008, 07:52 PM

I'm new and no nothing of the frame construction of your 84 but wondering if it would not be possible to cut the bad section out and replace it with a donor? It would take someone with some real welding skills and some engineering so it had the same strength or better.

firemanharry · #4 (**permalink**) 01-05-2008, 11:00 AM

You won't have a problem with a YJ frame. It won't be a direct bolt-on, but with a little work you'll be happy with the advantages of the YJ frame.

It's probably not worth a patch job. We've found that when you start cleaning the frame to find a good spot to weld, the more rot your likely to find.

If it was the middle of the season I'd try to box up a quick patch, but since it's winter I'd tear it down and make a REAL project out of it.

dandoc · #5 (**permalink**) 01-05-2008, 06:28 PM

Like many others, the frame at the rear spring shackles was rusted through on my YJ. Since I don't know how to weld well at all, I took the frame to a professional welder. The more he worked on the frame, the more rust holes and damage he found. The result was excellent patchwork and I was very pleased with everything.

Perhaps you could patch the damaged area and not find more damage. Most likely you will find more rust and rot. Good luck with your project!

Junkpile · #6 (**permalink**) 01-05-2008, 11:18 PM

Repairing the original frame is an option, but it has to be done right. There are certain procedures and methods involved in repairing a frame that you need to make yourself aware of if you've never tackled a job like this.

That said, I'd go with the YJ frame. It's a better built and more rigid frame. You won't just be repairing(with more failures to probably follow) a stock frame, you will upgrading, and it gives you a chance to more easily address any other issues.

PhattyX · #7 (**permalink**) 01-06-2008, 12:46 PM

Thanks for the input, guys. Patching the current frame is an option I considered, but I know there's at least one other spot starting to rot. So, I might as well go with replacing the frame.

I'd like to protect the frame while I'm doing all this. Does anyone know about galvanizing? I've also heard about a special paint technique where they electrify the steel first which makes the paint adhere to it... or something like that.

Thanks again,

-X

currupt4130 · #8 (**permalink**) 01-06-2008, 12:51 PM

The YJ frames are pretty good about not rusting. POR-15 is a good option though if you want to rust proof it.

dandoc · #9 (**permalink**) 01-07-2008, 10:30 AM

After my YJ frame was repaired (patched), I used Eastwood Co.'s Rust Encapsulator on the areas of the frame that had lost the factory black finish coating and were rusting. After the rust treatment, I painted the entire frame and the transmission crossmember with Eastwood's Extreme Chassis Black Satin. When applied correctly, the Rust Encapsulator is supposed to be better than POR-15 at preventing a recurrance of rust. So far, I haven't had any problems. Just give any product you use plenty of time to dry in humid conditions.

As for that special paint technique where the steel is electrified first... I think you're talking about powdercoating. The positively-charged dry paint powder is attracted to the negatively-charged steel and a temporary bond is formed. The coated steel is then baked in an oven to melt the paint powder in place. The result is a very durable and attractive finish on the steel that lasts for years and can withstand a lot of abuse.

redrooster · #10 (**permalink**) 01-07-2008, 01:29 PM

I have a YJ frame under my CJ. It seems like 6 of the 8 mounts will line up. The two that didn't are the ones directly in front of the rear tires. I want to say that I had to modify the grill mount also. Also, the YJ frame is wider in the engine area. I don't remember if it is wider throughout the full length of the frame or not. You'll like the YJ frame under there. I have beat the snot out of my Jeep since putting the new frame under and haven't had any issues with cracks or bends like I did with the CJ frame.
PM me if you want me to measure anything.

currupt4130 · #11 (**permalink**) 01-08-2008, 12:17 AM

Quote:

Originally Posted by dandoc

As for that special paint technique where the steel is electrified first... I think you're talking about powdercoating. The positively-charged dry paint powder is attracted to the negatively-charged steel and a temporary bond is formed. The coated steel is then baked in an oven to melt the paint powder in place. The result is a very durable and attractive finish on the steel that lasts for years and can withstand a lot of abuse.

Anything on my rig that was powdercoated quickly wound up chipping and flaking. I've never been very impressed with it.