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258 rebuild

What is the engine in? Sounds like a Jeep engine. If thats what it is, a Jeep manual from Haynes, Motors Manual, or Chiltons, will have the specs you need for an overhaul. Just get the manual covering your year of production.

What is the engine in? Sounds like a Jeep engine. If thats what it is, a Jeep manual from Haynes, Motors Manual, or Chiltons, will have the specs you need for an overhaul. Just get the manual covering your year of production. You may have to go to an AMC manual to get your information other wise.

I presume you are talking about the 258 cubic inch inline 6.
 

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A factory service manual might be useful, check E-bay or one of the Jeep specialty houses..... I paid about $100 for my reprint but on Ebay you might do better.

Chiltons or another aftermarket book would be cheaper but less complete, would probably do the job if you are experienced or have experienced friends to ask.
 

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engine manual

If you look at some of the Jeep enthusiast sites on the internet, you may find the manual and be able to down load it from the site as a freebie. I did this for my 79 XS1100 Yamaha Special.

I got the entire factory manual for 0$$. All 98 pages, and all it took was the time to down load it. Then I put it on a CD and printed it out.
 

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Note that the AMC/Jeep 258 was made from 71-89. 71 block and crank are different from later models due to a change in transmissions (71 is the only year that will use a Borg Warner automatic, in 72 AMC went to Chrysler sourced auto trannys). The crank snout changed in 87 to be 0.33" shorter, just like the 4.0L (which replaced it entirely by 1990). There are some differences in the heads over the years, but most interchange. The 4.0L head fits the 258 block and has smaller ports but much higher flow due to a better port shape. The 4.0L block has a bigger bore than the 258, but is identical to 75+ 258 blocks EXCEPT the 4.0L has no provision for a mechanical fuel pump. So you stick a 258 crank and rods in a 4.0L block and you get a 4.5L w/standard bore (4.6L 0.030" over). You also get a 9.5:1 compression ratio, which the EFI doesn't like, but would be great with a carb intake. Lots you can do with it! Clifford makes a wicked tripple Weber setup for it, one barrle per cylinder, but that's a bit expensive. Great power and throttle response once set up right though!!
 

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Most of the Jeep 258's had the two barrel Carter BBD. I think a few may have had a one barrel, and I think some also had a two barrel Motorcraft -- replacing the Carter with a Motorcraft or a Weber is a popular modification if you don't have short-arm inspections from the smog police...

Triple deuces is a lot of carb for that motor but it would look cool. A big two barrel (350 -500 CFM) seems to be simplest and most popular.

I have read quite a bit about putting 4.0L heads on them with the 4.0L EFI, but that's a lot of money and trouble for a simple stump pulling six that will do pretty good with a carb. I think a lot of the folks doing the EFI were frustrated with the finicky fussy hard to keep running good Carter BBD, and lived somewhere that insisted on the smog controls so that the simple carb wasn't an option.

I am still fussing with my BBD but it was running a lot better after a rebuild and clean-up -- unfortunately other problems are keeping me from finishing the tuning.
 

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500 cfm is the most you want for a 258. The EFI is well worth it and relatively easy though. Just pull the wiring harness and computer with everything attached and connect the ignition wire -- that's it. The 4.0L head takes just a little more work, but not much. What you have to be careful with is compression and cam specs with the 4.0L EFI system, especially the 1991+ system (87-90 is a little more tolerant, but you still have to be careful). Over 9.0:1 limits your cam choices (higher overlap to limit cylinder pressure). Put a 4.0L head on a 258 and compression goes to something like 9.5:1, so there is pinging problems with the EFI conversion. If I were rebuilding a 258, I'd throw the block and head out and buy a rebuilder 4.0L instead, use the 258 crank and rods with the 4.0L block and head. Use Silvolite 4.0L replacement pistons and machine the dish 1/16" deeper but the same shape. Badger pistons won't take that depth and still be reliable! The deeper dish brings compression back down to 8.8-9.0:1 range (stock is 8.7:1), which will work with the stock cam. You need 24# injectors also. That gives you a good 245-250 hp and 300-320 ft/lbs of torque. You might need an adjustable MAP sensor (easy to make -- adjusts the input voltage) to fine tune it, but it will generally run great on regular fuel. Without the additional dish compression is 9.5-9.7:1 and you'll need to run premium fuel. The adjustable MAP may be required as well. I could run midgrade before I dished the pistons, but got pinging under load -- had to be careful driving. The engine runs MUCH better now that the compression has been lowered, with no power loss. I'm using the 87-90 EFI system which has a knock sensor (91+ doesn't, main reason it's more sensitive to compression). Since the knock sensor was no longer retarding timing, so I might even have a little more power -- seat-of-the-pants "dyno" says it's the same or more though!

If interested go to Yahoo groups and look up "strokers". That's the name of the 4.0L/258 crank hybrid group. Of course I'm a member! I was the first to put such an engine in a car (check out my album), might be the only one! Most of the builders are Jeepers. I've got as much power and torque as a 74 AMC 360/4V, and it shows!
 

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I am in the process of gathering parts and building a 258 with a 96 head the intake from the 86 258 will work on the newer head you will have to alter the dowl hole on the intake to fit onto the newer head. Be careful not to grind into the waterjacket. Also there is a little grinding to be done on the intake to make the old exhaust manifold. But I belive I will be getting a 96 exhaust manifold so I don't know about the grinding on the intake to fit the exhaust.:)
 
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