Pile of Parts - What Would You Do?

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Eagle_Fly_Free
Posts: 2
Joined: April 8th, 2023, 3:05 pm
Vehicle Year: 1988
Vehicle Make: AMC
Vehicle Model: Eagle

Pile of Parts - What Would You Do?

Post by Eagle_Fly_Free »

Hey Everyone! I'm working on a 1988 AMC Eagle with the 4.2 and automatic. I am wondering what ya'll would do with the following available to you (with the caveat that I've already spent thousands on the following parts/components+ and would like to spend as little more money and time as possible):

1. 1988 AMC Eagle 4.2 complete engine/car. The block is cracked in 2 places and head is slightly warped. My machinist thinks the crank could use a slight grind but looks good otherwise. No spun bearings and the engine ran so I think the connecting rods are ok. I've purchased everything for a cooling system rebuild and the radiator has been re-cored.

2. 1998 Wrangler 4.0 complete engine with mpfi/harness/ecu. "Ran well" when pulled. Low compression on cylinder #1, no change with oil in cylinder. So likely a blown head gasket and/or (hopefully not) a cracked head. Removing the head for inspection tomorrow.

3. Comp Cams mild/torque cam (232-4) 800-4800 rpm, Comp lifters, pushrods, std valve springs, rockers, Comp timing set. Purchased for the 4.2 but seemingly all compatible with the 4.0.

4. Aces brand "Deuces Wild" throttle body EFI with spark-controlled distributor, fuel pump/regulator/lines (350hp capable with dual 100lb/hr injectors).I bought this for the 4.2 before I knew it had a cracked block.

Originally I just wanted to get the Eagle running and use as a daily driver... well sadly, cans of worms were opened. But I find myself having most of the parts for a stroker build for potentially little more money.

A. My machinist is months behind on work. Is it at all reasonable for me to think I might be able to avoid all machining with a 4.5 build? i.e. drill hone cylinders, new std-size crank bearings, fine sandpaper on 4.2 crank (there are no gouges), new std-size rod bearings, reuse the 4.2 rods, swap to 4.0 std pistons without a special press (?), change to aftermarket cam without changing the cam bearings (or leave the 4.0 cam in place?), new piston rings, rear and front oil seals? I think most of you will tell me to just have the machine work done to avoid having to do it all again in 20k miles!

B. In the likely event that I do have all the appropriate machine work done, seems like a 4.6 build would be better and less stressful on the engine & starter (lower compression) as well as my wallet (87-89 octane). Except those custom $700 pistons! Anyone have a source for cheaper pistons that would work with the 4.2 crank, 4.0 rods combo?

C. Is the factory Jeep mpfi/ignition system going to be a lot better than the aftermarket TBI I bought (whether stroker/cammed or unmodified 4.0)? I really am not looking forward to the prospect of adapting the 4.0 mpfi harness to the Eagle's electrical system and am more interested in simplicity and reliability than tons of power. My old Chevy 350 with TBI was one of the most reliable engines I've owned...

I apologize for the length and thank you for your insights.
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Cheromaniac
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Re: Pile of Parts - What Would You Do?

Post by Cheromaniac »

I'd have a machine shop check the cylinders in your '98 4.0 block for roundness and taper. If they're still within factory tolerances (doubtful), you could use standard size 4.0 pistons together with your 4.2 rods. However I think it's more likely you'll end up going to a +0.020" or +0.030" overbore.
The same machine shop can also check the main and rod journals of your 4.2 crank, determine if they need to be reground 0.010" undersize, and polish them.
I built my stroker short block nearly 20 years ago with a +0.020" overbored '00 block, 4.2 crank, 4.2 rods, and Silvolite 677AP pistons. After polishing the piston dishes, the dish volume came in at 17.7cc. The static compression ratio was 9.25:1 with no decking of the block surface and 57cc combustion chambers (measured). I could run it on a mix of 87 octane during the cooler months without any pinging but I mostly ran it on 91 octane.
1992 XJ 4.6 I6 - 5MT - Stroker build-up, Stroker "recipes" Sold
1995 Mustang GT - 4AT - Modded Sold
2006 Mustang GT - 5MT - Modded Midlife Crisis Car :mrgreen:
Randy Bobandi
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Re: Pile of Parts - What Would You Do?

Post by Randy Bobandi »

Eagle_Fly_Free wrote: April 8th, 2023, 6:30 pm


A. My machinist is months behind on work. Is it at all reasonable for me to think I might be able to avoid all machining with a 4.5 build? i.e. drill hone cylinders, new std-size crank bearings, fine sandpaper on 4.2 crank (there are no gouges), new std-size rod bearings, reuse the 4.2 rods, swap to 4.0 std pistons without a special press (?), change to aftermarket cam without changing the cam bearings (or leave the 4.0 cam in place?), new piston rings, rear and front oil seals? I think most of you will tell me to just have the machine work done to avoid having to do it all again in 20k miles!

B. In the likely event that I do have all the appropriate machine work done, seems like a 4.6 build would be better and less stressful on the engine & starter (lower compression) as well as my wallet (87-89 octane). Except those custom $700 pistons! Anyone have a source for cheaper pistons that would work with the 4.2 crank, 4.0 rods combo?

C. Is the factory Jeep mpfi/ignition system going to be a lot better than the aftermarket TBI I bought (whether stroker/cammed or unmodified 4.0)? I really am not looking forward to the prospect of adapting the 4.0 mpfi harness to the Eagle's electrical system

I apologize for the length

Forget the machine shop. Dingleberry rebuild the 4.6L. Run a hone through the cylinders, run tube brushes through the lifter bores and oil galley, flat block/sandpaper the deck surfaces, sandpaper polish the 4.2 crank, leave the stock cam bearings in it, use the cam that you have, get rods and pistons from Russ, get a Cometic head gasket, wire brush the valves, cartridge roll the ports and port match the intake ports to the intake manifold, run a tube brush through the valve guides and lap the valves/seats.

Forget 87 octane and the Stock Jeep ECU. Run 10:1 compression on 93 or E85 with the TBI kit that you have and get an adjustable timing set. Super simple, clean, and more power potential. Are you running Aces' High Roller Pro Ignition as well? That would be a sweet setup in the Eagle. The stock Jeep computer with the tiny injectors will result in stock power output, regardless of the slight increase in displacement in the form of stroke. Stock computer stuff and HP Tuners is a thing of the past due to EPA overreach. FuelTech, Carburetor, TBI are the options. I would love to have a TBI Stroker Eagle with 220 Wheel HP just to do burnouts in.
Eagle_Fly_Free
Posts: 2
Joined: April 8th, 2023, 3:05 pm
Vehicle Year: 1988
Vehicle Make: AMC
Vehicle Model: Eagle

Re: Pile of Parts - What Would You Do?

Post by Eagle_Fly_Free »

Well, I stripped down the 4.0 today. It does look like the head gasket was possibly leaking around cylinder 1 but I can't tell for sure. Cam and lifters show wear and the cross-hatching from an apparently somewhat recent honing are very clear on the cylinders. Looks like it was drill-honed, not bored. I'm going to take the head to the machine shop to check for cracks; have it decked and valve lapped. So I might as well take the block and 4.2 crank.

Thanks to you guys and other posts in this forum, I've sort of narrowed down the build. Most likely a lower compression 4.6 with the aftermarket EFI/Ignition system and the 232-4 comp cam I bought for the 4.2. I found the Keith Black stroker pistons on summit for a lot less than I was initially thinking the pistons would cost but will probably reach out to Russ Pottinger about his connecting rod/piston options.

I dry fitted the 4.2 intake to the head and see what people have told me about the intake ports and dowels not lining up. Does anyone know specifically what carb/throttle body adapter would mate a Holley 2300 carb flange to the 4.0 MPFI intake? Thanks.
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