Thread exclusively to discuss the best ways to build Jeep I6 Stroker motors

[Rescue Diver]

I decided to go straight to the horses mouth regarding the difference in the 4.0 and older AMC 258 i6 / 4.2l oil pumps, so I called Melling Tech Support. The pumps are swappable. The M-81A that's what the 1995 4.0 calls for has a 5 lb higher spring rate than the M-81 that my 1979 AMC 258 i6 / 4.2l has. I ordered a Melling high volume pump from Advance Auto for only $77, and since I ordered online, I got 15% off of that!

 

[Rescue Diver]

How many miles does I have on it?

I have no idea on the miles, but it's very clean looking, and as long as the block isn't cracked, I'm good to go since everything will get machined anyway.

That looks new, what did it set you back. details man details

I only paid $100 for it, and it came from a trusted member of the KC Jeep Club. He says it ran fine when he pulled it out of an old 95 Cherokee, but had a small tick. Probably a lifter needing adjusted, but even if it was a rod knocking, who cares? I'm not using the 4.0 crank or rods!

It also came with the 95 intake, throttle body, injectors, and fuel rail in case I ever decide to cross over to the dark side.

In the mean time, when that big EMP hits, I'll be thinking of all of you computer controlled guys that are stranded.

 

[coldair]

I've came across that site when I was trying to decide on building my AMC 258 i6 / 4.2l or building a 4.0 stroker. Some good info

 

[Rescue Diver]

I say go as low as you can when boring, in case you need to go higher later or keep the engine long term and need to do again.

What'll decide my over bore is piston availability. If I can get 60 over pistons for the same price as 30 or 20, I'll go that rout. I expect the engine to work fine for as long as I want it to, and if something ever did happen to damage a cylinder, I'll just scrounge up another block. I already know three or four guys that have 4.0 blocks just laying around.

 

[tarry99]

I read that the early heavy ones like mine are strong, but I haven't read anything about the newer ones breaking, so I don't think it makes a lot of difference.

Rescue

Here is a Stroker crank for you........tons of torque on this one and real heavy, might have to shorten it a bit.............LOL

 

[Cheepjeep85]

thats a hell of a deal on that motor

 

[Rescue Diver]

I tore it down this afternoon and everything looks good. The cylinders are glazed and don't have much cross hatching left. They have very little ring ridge and no scars, so they should clean up nicely.

 

[Rescue Diver]

I finished cleaning up the block this afternoon. The pistons that came in it say 50 on top. For a second it had me worried that the motor had already been bored, but I've never seen a 50 over piston? I got out the digital caliper and the bore is standard at 3.875" so no worries. The main bearings look brand new, but since I'm not re-using the 4.0 crank, that doesn't mean much. Lol

I also grinded out the holes that allow the oil to drain from the top of the motor to the pan. The casting has what's supposed to be inch long by 3/4 inch openings, but the factory casting process leaves the holes 2/3 blocked. They're now completely opened. With the high volume pump, I need to oil to drain back to the pan as fast as possible.

 

[Rescue Diver]

I decided to go with Sealed Power 60 over, dished cast pistons with coated skirts from Summit Racing.

They're a special order, so they won't ship for more than a week.

Manufacturer's Part Number Z677CP60
Summit Racing Part Number SLP-677CP60
Bore (in)3.935 in.Bore (mm)99.949mm
Piston Style Dish, with a D-shaped cup
Piston Material Cast aluminum
Compression Distance (in)1.585 in.
Wrist Pin Style Press-fit
Pin Diameter (in)0.931 in.
Piston Ring Thickness 5/64 in. x 5/64 in. x 3/16 in.
NotesDurOshield ® coated piston skirt. Recessed piston head is 0.116 inch deep.

 

[1986cj7]

Just one question. What is the price differance between rebuilding a 86 AMC 258 i6 / 4.2l , or building a stroker for my 86 CJ7 ?

 

[Rescue Diver]

Just one question. What is the price differance between rebuilding a 86 AMC 258 i6 / 4.2l , or building a stroker for my 86 CJ7 ?

If you already have a good AMC 258 i6 / 4.2l crank and rods from your old motor, and you planned a total rebuild anyway, the only difference is rounding up a serviceable 4.0 block, and switching to an electric fuel pump.

One other thought. You're still running the stock 86 AMC 258 i6 / 4.2l head instead of a 4.0 right?

If so, your head won't work on a 4.0 block unless you have it drilled out for 1/2" head bolts. But why would anyone in their right mind bebuild a stock AMC 258 i6 / 4.2l head when they could have a huge hp and mpg increase with a 4.0 head, and they're for sale everywhere. I have a spare 7120 head just sitting around doing nothing from the 1995 4.0 I bought for the block.

 

[Rescue Diver]

An update on my build. I'm re-using the stock 4.0 high output cam, but decided to buy new sealed power lifters from Advance. They have a 20% discount today only on web orders, so I grabbed the set for only $41 including tax. I have a line on some 10 under rod bearings from one of our fellow Jeep-CJ members, so the only parts left to buy are the 10 under main bearings. My local machine shop will install new cam bearings as part of the $180 they charge to bore and tank the block.

 

[1986cj7]

If you already have a good AMC 258 i6 / 4.2l crank and rods from your old motor, and you planned a total rebuild anyway, the only difference is rounding up a serviceable 4.0 block, and switching to an electric fuel pump.

One other thought. You're still running the stock 86 AMC 258 i6 / 4.2l head instead of a 4.0 right?

If so, your head won't work on a 4.0 block unless you have it drilled out for 1/2" head bolts. But why would anyone in their right mind bebuild a stock AMC 258 i6 / 4.2l head when they could have a huge hp and mpg increase with a 4.0 head, and they're for sale everywhere. I have a spare 7120 head just sitting around doing nothing from the 1995 4.0 I bought for the block.

If I would have know this do you think I would have asked the question? Wont be asking any more questions in your threads again.

 

[Rescue Diver]

If I would have know this do you think I would have asked the question? Wont be asking any more questions in your threads again.

OOPS! I guess I should have worded that differently.

What I should have said is once you know the big difference in horsepower and mpg you get with a 4.0 head over a stock AMC 258 i6 / 4.2l head, why spend the money getting the stock one rebuilt when you can switch?

 

[Rescue Diver]

I've almost run out of things to do on the new motor while I'm waiting on parts.

Today I took apart, cleaned and polished the 4.0's aluminum oil filter adapter. Then I ran by Ace Hardware and picked up new O-rings for it. I then went to Advance Auto to get a new filter. The 95 motor calls for a L14670 Purolator, but I found that a L30001 fits the adapter just fine and is way bigger, so I went with that one.

 

[Petescj]

Thanks. Keep on giving us the detail and part numbers.

I've almost run out of things to do on the new motor while I'm waiting on parts.

Today I took apart, cleaned and polished the 4.0's aluminum oil filter adapter. Then I ran by Ace Hardware and picked up new O-rings for it. I then went to Advance Auto to get a new filter. The 95 motor calls for a L14670 Purolator, but I found that a L30001 fits the adapter just fine and is way bigger, so I went with that one.

 

[Rescue Diver]

Thanks. Keep on giving us the detail and part numbers.

Here's the basic recipe for the one I'm building. I hope we might have others on here that have built their own versions so they can share their recipes and experience.

4.0 Block 1995
AMC 258 i6 / 4.2l 3.895" stroke crank
AMC 258 i6 / 4.2l 5.875" rods
Sealed Power 677CP +0.060 3.935" bore pistons
Stock 4.0 87-95 H.O. camshaft
Sealed Power HT-2011 Lifters
H.O. 1995 #7120 1.91"/1.50" cylinder head
0.043" head gasket
0.088" quench height
Melling M167HVS High Volume Oil Pump(Had to massage the oil pan for clearance)

It should be in the neighborhood of 9.25:1 compression.
Jeep4.0performance.4mg.com says I should expect the following numbers with this combo, but since I'm not running fuel injection, I'll probably be just under that.

248hp @ 4900rpm, 306lbft @ 3250rpm

 

[IOPort51]

248hp @ 4900rpm, 306lbft @ 3250rpm

I am wondering what the numbers are at realistic RPMs.

If you have to go all the way up to 4900rpms to see any advantage your going to spend a lot of time in 2nd gear. Has anyone seen any numbers for something in the range of 2-3000rpms?

 

[Petescj]

248hp @ 4900rpm, 306lbft @ 3250rpm
I am wondering what the numbers are at realistic RPMs.

Good point. Im thinking the low rpm torque would be what Id look at.

 

[Rescue Diver]

Here's the torque chart they have posted. It lists stock 4.0, modified 4.0, and Stroked 4.0. I wish it had the stock numbers for a AMC 258 i6 / 4.2l included.