Jeep Strokers

1979 CJ 7

So the story goes like this....

AX15 swapped onto my 258, which is a common swap with people doing stroker motors that use the 258 crank. I called advanced adapters and ordered one of their specific pilot bushings. Ended up cracking the case on my AX15 and had to pull it down, except it wouldnt come out. We had to bend some wrenches and do some prying and unbolt the pressure plate from the fly wheel to get the trans down.





You can see where the pilot bearing was actually riding inside the crank instead of on the end of the transmission input shaft.

Advance Adapters comped me a new pilot bushing (same one). and I gave it another go, assuming that it was a QC issue. After I put it all back together, the motor had a hard time running. It wouldnt idle on its own, would bogg down and stall out after a minute or so, and in general just felt like it was dragging. When I tried to turn the motor over by hand, I COULD NOT do it with the trans installed. It took 57 ft-lb of force to turn the motor with not spark plugs and no transmission attached. This led me to get a hold of an orthescope and checked the cylinders. On the camera, it appeared that the #1 piston was cracked, so I pulled the head. As luck would have it the #1 piston was fine, the reflection of the LED light on some casting flashing on top of the piston made it look like a crack that wasn't there. Even with the head off, it still took 54 ft-lb of torque to turn the motor over. Keep in mind that this motor only has 25,000 miles since a professional shop rebuilt it with all new internals (crank, rods, 0.030 pistons, cam, ect). So the motor came out and the bottom end was inspected. The pilot bearing that I was told over the phone was supposed to be the correct part for my application (AX-15 to 258 crank) was obviously incorrect. This forced the crank forward, putting a great deal of thrust force on the main bearings. If I did not take the motor apart when I did to inspect it, the motor would have surely destroyed itself beyond reasonable repair in another couple of months time. Since I caught it in time it seems that the crank was not damaged and only the main bearings, rod bearings, rings, block dip, magniflux, and honing are needed to revive it and get it up and running asap.

I have been in contact with Advance Adapters throughout this process, and after some emails and a phone call yesterday they are willing to work with me on paying for the parts to fix the motor. They offered me an amount yesterday that would not cover all of the major parts and cleaning, so I made a counter offer, and I'm waiting to hear back from them today. I would be VERY shocked of they do not want to meet my request. I COULD be a real jerk in this situation and tell them that Im dropping the motor off at a shop and will be sending them a $1,400 bill... but instead Im willing to take my personal time and effort to fix the damn thing as long as they cover all of the parts, which I think is DAMN reasonable!


25k miles, and its in 1000 pieces again...
















SOOOO now that we are all on the same page, here is what I'm thinking... Keep in mind, I'm a complete noob to the fine details of building a stroker

Ive got a 4.2 crank and connecting rods that seems to be undamaged to the naked eye (needs checked). There's a 4.0 head (7120 casting) with 7k miles since I swapped it onto the 4.2. I need to buy main bearings, rod bearings, rings, and gaskets ANYWAY. Why not throw a little but more cash into it and have a stroker??? Im missing prime PA wheeln and cruiz'n so Im trying to get this back on the road ASAP and inexpensive. I would like to run pump gas (high test ok), use stock 4.0 cam, and convert the CJ to MPI at the same time.

What Ive Got:

4.2 crank (25k miles)
4.2 rods (25k miles)
4.0 head (7k miles) 7120 casting
99 4.0 intake and stock injectors

What I need:

4.0 block (lots to be had)
OBD1 computer and wiring harness
Pistons???? stock??? dished????


Now I've got one more idea to throw out there... don't laugh....

For the sake of getting this back on the road before summer is over, any thoughts on just running the stock Carter Carb (rebuilt a month ago) just so I'm back on the road ASAP with a good running motor, and then fool with figuring out how to splice the wiring harnesses later????

OR

I could just get the parts to put my 4.2 back together and continue running the 4.0 head and carb and focus on the MPI conversion with that.

with the obd1 system, it actually ends up being only like 4 wires to convert it, but if you poke around on some amc or jeep forums there will be more info there. i know the obd1 swap is very common, and theres alot of help available. i also know that a stroker will in fact run on a carb, theres a guy on an amc forum that is running a 4.5 stroker with a carb in an amc eagle and its been going fine for a while. im not sure if he has done anything other than a 4.2 crank and rods tho.

Ive been doing a lot of research the last few days on the stroker subject.

1) I had work done to the 4.0 head before I put it on the 4.2. I do not know if they decked the head or not. How do a measure to determine what has been done?

2) For determining quench and compression... do I need to have the block sent to the machine shop first to see if it needs to be decked before I decide on pistons??? Ideally I would like to use the 4.0 stock pistons and cam. Is this going to cause too many ping headaches once I get it all together?

I'm new to the whole engine building gig, and I just want to make sure that I've got my info/measurements straight before it costs me more money that it needs to.

easiest way to check for decking or not on your head would be to measure the CCs of the combustion chamber, and compare that number to stock. the stock number should be around here somewhere. with vaseline, a piece of plexi and some coloured water and a graduated cylinder or a big syringe would probly work too. use the vaseline to seal the plexi to the head, and the valves to the head. then using your liquid measuring device, fill the chamber and check how much fluid it took to fill it.

as for the block, i believe you actually need your pistons youre going to use before you know your deck hieght. however, id have the block to the machinist first so he can measure how big of pistons you need to be buying. you will need new ones, depending on your choice of rod. if you use the short rods which you already have, assuming they are good, as well as the crank (with your situation with the pilot bearing, id have the thrust surfaces checked on the crank), you can use stock style 4.0 pistons, perhaps overbored to take out any roughness in the cylinder as necessary. if you decide to use long rods from the 4.0, youll need to buy special pistons.

for the cam, if you decide to use a stock 4.0 cam, id grab the lifters and reuse them, in the same spots they are in the 4.0. that will save you cam break in, and the money for the cam.

ping and quench will depend on your pistons and rods, and the deck hieght of your block, and the dish of the piston, as well as the compression ratio that they all create. after you have your pistons, head and block all together, you can start figuring out that part. good luck!