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Old 10-28-2017, 02:54 PM
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AMC 4.2 TO GM 4.2 Swap Thread Information

On another Yj Tech thread, cobra30689 requested I post a bit of what I've been up to with regards to my Yj update project. This will not be a build thread, or a sales thread. Just a few pictures and I will offer to answer any technical related questions that I can. Please keep it technical. Don't bother to suggest that I should have just done a V8. I've done that before.

That said, my swap is really more of a restoration. My curiosity is seeing what drive line combo I could swap in that didn't require adapters. This doesn't include making any missing parts along the way that cannot be purchased. Far from being done. Nothing gets done fast around here and I don't have a time line.

My swap specifics.

1987 Jeep Yj Base
Original Dana 30 front with 3.54 and updated braking.
Rear typical matching Ford 8.8.
2.5 inch Rancho spring lift.
31 inch Toyo AT2's on TJ Ravine's.
2008 Vortec 4200 running MS3Pro
2010 Aisin AR5 5 speed combined with AX15
NP231J

A few engine related pictures.

Cornchip.

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Old 10-29-2017, 05:38 PM   #2
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Well slow moving me just found this and suddenly realized why Cobra and Cornchip kept going back and forth. For a while I was starting to think you two were the same person.

What are your plans for a radiator?
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Old 10-29-2017, 11:39 PM
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What are your plans for a radiator?
The 4200 can use a stock Wrangler YJ/TJ radiator. So I'm using a two core plastic/aluminum. What I can't use is a mechanical fan. The 4200 has offset the water pump slightly to the drivers side and makes it too difficult to center on the core. I'm going to try the proven Taurus 2 speed electric fan. There is enough room as this motor is nearly identical in length to a 4.0 litre. Should be fine controlled by MS3. I have also changed the alternator from the stock 2 pin ecm controlled unit to a good old fashioned GM CS144 to make sure I get the amps I'll need.
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Old 10-30-2017, 12:20 PM   #4
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Very cool. I like the outside the box approach. I have an 04 Trailblazer and that has been a great engine. I added a high flow cat when the original clogged up and that really woke it up too. There is a square body chevy with one of those swapped in over on 67-72chevytrucks.com
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Old 10-31-2017, 05:04 PM
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I have an 04 Trailblazer and that has been a great engine.
I also have a 07 Trailblazer as my daily driver. In many respects the TB is a far better vehicle than the YJ just about any way you want to compare it. But it will never be a Jeep.
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Old 11-06-2017, 05:05 PM   #6
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You may have mentioned this in my post where this started, but I don't remember.....are you running the GM PCM or going with Megasquirt?
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Old 11-06-2017, 05:06 PM   #7
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EDIT: I missed the MS3Pro in the first post lol
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Old 11-06-2017, 05:43 PM
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While the plan is MS3 Pro, I have the original PCM, harness and throttle body with gas pedal should things not go my way (2008 PCM can be programmed as most any LS for stand alone). Several guys have run the MS3 primarily for the ability for boost. That won't be me. I just don't want OBD2 and electronic throttle control. I ended up making an adapter to use the 68mm Jeep Grand Cherokee 4.7l throttle body. It has a throttle cable compatible with the YJ's firewall and existing pedal.
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Old 11-06-2017, 06:00 PM   #9
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What modifications do you need to do to get the AX15 to bolt up to the GM motor?
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Old 11-08-2017, 07:15 PM
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What modifications do you need to do to get the AX15 to bolt up to the GM motor?
I originally planned to use the AX15, but decided against that route as both the Ax15's I had on hand needed rebuilds. Since I had to buy a bell housing from a Canyon/Colorado....I then bought a complete low mile AR5 from a 2010 Canyon 4x4. The AR5 is more or less a newer AX15 with a few changes.

Gear ratios... AR5 1st - 3.75 Ax15 1st - 3.83
2nd - 2.26 2nd - 2.33
3rd - 1.37 3rd - 1.44
4th - 1.00 4th - 1.00
5th - .73 5th - 0.79
rev - 3.83 rev - 4.22

Other differences, the AR5 has a 26 spline input and 27 spline output. Also the extension housing has an upside down 5 bolt transfer case pattern that is 1.9" inches longer OAL.

So what I ended up doing is removing the AX15 extension housing and bolting to the rear of the AR5. A modification to the AX15's shift tower finger had to be made to match the AR5's and casehardened again. Then I had to deal with the longer output shaft by making a spacer. The 231J had to have an input gear change to 27 splines removed from a 241C. The transfer case shift linkage required lengthening and welding.

As far as the clutch goes, I had to make a flywheel as these 4200 never had a manual from factory. Also from GM, a clutch pressure plate and disc from a late 80's Camaro/Firebird. It's the same pressure plate as a similar vintage 4.2 with the exception of the 26 spline disc. A GM internal hydraulic slave will be used, not the plastic thingy the YJ's came with.

Pictures.
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Old 11-08-2017, 07:20 PM
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Old 11-08-2017, 07:26 PM
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Old 01-18-2020, 04:31 PM   #13
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I realize I'm a little late to the party, but how did you make the flyhweel? I'm seriously considering this swap, but the flywheel is a major issue that might force me in a different direction.
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Old 01-19-2020, 12:04 PM
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I realize I'm a little late to the party, but how did you make the flywheel? I'm seriously considering this swap, but the flywheel is a major issue that might force me in a different direction.

Never too late to a party. Yes...I had to make my own flywheel from measurements derived from the 6 cyl flex plate and a manual flywheel from a 2.9 4cyl. A Facebook group exists where they talk about making a batch of flywheels, but it is just that....talk. It's going to be an issue finding one.



Facebook LINK.




So I am still working away in my spare time and haven't given up. The restoration side of my build is very time consuming. More than I expected.


Last picture taken of the Jeep. Lots of under dash work to complete over the winter.



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Old 01-19-2020, 02:14 PM   #15
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This is a really neat project, I've always liked the 4200 atlas motors just didn't go this route for lack of documented support. Your stock ax15 output shaft would have gone into the AR5 and saved you a few inches on overall length though. I built an ax15 for someone with gears out of a G452 from a toyota dyna truck with ratios: 5.15 2.74 1.93 1.00 0.73 r5.04 which was pretty cool. Nice deep first and good overdrive compared to stock. Amazing how much interchangeability these transmissions have as long as you have the right countershaft to match the gears.
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Old 01-19-2020, 02:40 PM
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I also have little doubt the late model AX15 output shaft would have worked. My only issue there is disassembling a perfectly good transmission to make it happen. I made up the length difference with a Terraflex Extreme Short SYE. So no issues there.
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Old 01-19-2020, 02:45 PM   #17
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I understand, a gearbox disassembly can seem very daunting. But overall, very awesome project, I hope it gets updated soon with more pictures and possibly videos when it is running!
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Old 01-19-2020, 02:47 PM   #18
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That type of thing always takes forever.

So to be clear, you purchased a blank flywheel, drilled the holes and bored out the center based on the 4200 flexplate and 4cyl flywheel. OR did you modify the 4cyl flywheel using the 4200 flexplate by drilling out the center and redrilling the holes.
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Old 01-19-2020, 03:19 PM
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That type of thing always takes forever.

So to be clear, you purchased a blank flywheel, drilled the holes and bored out the center based on the 4200 flexplate and 4cyl flywheel. OR did you modify the 4cyl flywheel using the 4200 flexplate by drilling out the center and redrilling the holes.



Simple answer is I bought a C1045 blank and machined a new part rather than modify an old one. The more difficult answer, I decided to see if it were possible to modify and available 5 cylinder flywheel. Main difference between the 4/5 and 6 is the crank mounting flange is set .400" further back from the block to clear the counter balance shafts on 4/5 cylinder engines. So you'd face material off the backside of the wheel, which then you'd have to also relocate the ring gear diameter away the same amount. However...it is doable. The centre locating diameter is then bored to 2.0705" and drill a new bolt pattern 22.5 degrees out from the first at 3.346" BCD.


I tried this and just wasn't impressed with the look of it and made a centre hub from 4340 to beef it up some. I'll never run it as a single piece unit is far stronger. I like my feet and legs intact.


So....there is room to make an exceptionally heavy offroad worthy flywheel up to 1 5/16th's thick besting 30 lbs weight. My wheel is at 1 1/16ths (stock weight) and an aluminum spacer moves the slave back towards the stock Jeep 10.4" clutch.


My 5 cylinder LLR experiment below.










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Old 01-19-2020, 03:23 PM
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Old 01-20-2020, 09:53 AM   #21
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Good to see this thing still going. It has been so long since you updated that I forgot about it.
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Old 01-20-2020, 06:22 PM   #22
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Wow! It sounds like creating a flyhwheel is possible. I'll have to do a little more research on this. Thanks!!
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Old 01-20-2020, 11:53 PM
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Should have mentioned, use Ford M-6379-B Flywheel Bolt kit. Comes is a pack of 8 and are 26.5mm long. Clutch pilot bearing is a standard ACDelco CT1082.
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Old 01-25-2020, 08:06 AM   #24
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More Questions!

I'm still thinking about this. I joined the 4200 engine swap FB group. There's a conversation about using the Chevy 8 bolt flywheels that are used on the Gen V LT1 engines. I'm hoping that bears fruit because I doubt I'll be able to build a flywheel. I can cut steel and I'm a self taught welder ... not a machinist. For now, I'm planning on using an old 3.5.

I'm trying to figure out how easily this will fit and how I can make some motor mounts. I'm hoping to use the stock 2.5L frame side mounts (prefer not to cut the frame), and create some new engine side mounts. Do you think that's possible assuming a 4200?

I've found that the 4200 is about 4-5 in taller than the 4.0L ignoring the oil pans. Based on forum posts, the 4.0L is 18in from oil pan rail to valve cover. The 4200 is closer to 23in including oil thing on the front. Did that cause you a problem? Do you have a body lift?

Thanks!
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Old 01-25-2020, 12:34 PM
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The LS engines after 2009 called 'LSA' have 8 bolt cranks with an unknown bolt diameter and the 168 tooth ring gear. It won't likely be a plug ang play event by any means. Don't get your hopes up. FB has many dreamers and little tech.


Don't worry about it fitting in the engine bay. It's a big engine but has amazing side clearance over a LS while being no tighter to the rad than a 4.0 with accessories installed. an Efan is a necessity however. The engine is taller due the 4200 having a taller deck to support it's 4.010 stroke....but not by much. The height issue is more at the bottom because of the Dana 30's differential. Without a lift it would be very tight. I have a 2 1/2" lift and clearance is a non issue.


Motor mounts are best approached with a clean slate by removing any trace of the stock mounts. The 4200 has excellent adaptable mounts. You can use the factory brackets and mounts together and work out the rest. I did my setup with CAD to get everything right.


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Old 01-25-2020, 05:22 PM   #26
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They look amazingly similar. See the how the bolts line up 2 across, and the center even looks similar ( I realize that's how the 3.5 and 4.2 are).

I did an analyse of the flywheel picture using the outside diameter to generate in/pixel for the image. Using that crude method, I got 3.12in bcd and 2.08 in in diameter. That seems very close.
Even if the bolt holes and center boar are correct, the total FW diameter seems to large. I'm still hopeful.

https://www.gmperformancemotor.com/parts/12636325.html

I can appreciate a clean slate design, but its nice to keep the original mounts. After doing a little measuring, it looks like the original mounts are about 5 inches to far back to be used when swapping a 4200. The 3500 motor mounts are very different and do line up with the original jeep mounts. In addition the shorter length (about 5 inches) of the engine provide a bit more wiggle room.
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Old 01-26-2020, 09:56 AM
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They look amazingly similar. See the how the bolts line up 2 across, and the center even looks similar ( I realize that's how the 3.5 and 4.2 are).

I did analyze the flywheel picture using the outside diameter to generate in/pixel for the image. Using that crude method, I got 3.12in bcd and 2.08 in in diameter. That seems very close.
Even if the bolt holes and center boar are correct, the total FW diameter seems to large. I'm still hopeful.

Somebody on FB will have to buy one and get real measurements. No matter what, it will need to be reworked if there is material in the right places. And still it has to go on a lathe. Too much rework and it would have been smarter to make one from scratch. Who's going to go first?
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Old 01-26-2020, 11:34 AM   #28
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From Scratch

Maybe I could find a flexplate in the junkyard

Why would it need to be put on a lathe?

How do I make one from scratch? I realize that sounds easy to you, but I'm an electrical guy. I just don't have the skills.

Do you have a document or drawing that describes the flywheel's characteristics? I assume there's more to it than the center bore and bolt holes. Where would I get a blank flywheel. I did a google search without much luck(or maybe I just didn't understand what I found). I assume that's really just a solid ~13.5in x Xin round piece of hard steel. How much is a blank?

A machine shop would need to do the work for me. Do you think if I gave them a 4.2 flexplate they could make a flywheel? It sounds expensive if you can't do the work yourself.


Right now, I'm trying to crack the P12 PCM so I can change the VIN without having to give up my first born to EFIive or HPtuners.
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Old 01-29-2020, 09:51 PM   #29
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When the time comes I am either going to go this route or a 2.8 duramax out of a colorado. It will likely be 2 years since I dont have the space in my garage, or the time, to do it now.

I really wish they would have just skipped the 5 cylinder all together and put these in the gen 1 Colorado's. Hell I think a reworked and modern version of this engine would be better than the 3.6 that they put in the gen 2 colorados. With a little bit of rework could probably have a 350hp/350 tq motor. That would have also created the after market support for them too.
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Old 01-31-2020, 07:19 PM
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Maybe I could find a flexplate in the junkyard

Why would it need to be put on a lathe?

How do I make one from scratch? I realize that sounds easy to you, but I'm an electrical guy. I just don't have the skills.

Do you have a document or drawing that describes the flywheel's characteristics? I assume there's more to it than the center bore and bolt holes. Where would I get a blank flywheel. I did a google search without much luck(or maybe I just didn't understand what I found). I assume that's really just a solid ~13.5in x Xin round piece of hard steel. How much is a blank?

A machine shop would need to do the work for me. Do you think if I gave them a 4.2 flexplate they could make a flywheel? It sounds expensive if you can't do the work yourself.


Right now, I'm trying to crack the P12 PCM so I can change the VIN without having to give up my first born to EFIive or HPtuners.

Just reading the FB group today and read that one member is planning to combine a steel blank over a flex plate. Yuk. I had a similar setup in '95 from Advance Adapters on a SBC. I didn't last. I just can't stress how bad it was. The horror.



I really need to look into the true costs of making a batch. I just don't want to get get stuck with something I can't move. I wonder what the pent up demand really is?

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