258 rebuild - best donor 258 vehicle - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-14-2004, 10:04 PM Thread Starter
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258 rebuild - best donor 258 vehicle

I want to prepare for the inevitable engine rebuild by buying a used 258 and rebuilding it for the future. I currently have an 86 258 auto with 77k and bad blowby (I think the seals are going to go within the next 10k). I can find a few AMC's in the area and would like to know if one year block is more desirable than another. What would be a decent price for an old motor? Any block changes from previous years? My 86 block is stamped with an 85 production date if it matters.
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post #2 of (permalink) Old 01-14-2004, 10:32 PM
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Re: 258 rebuild - best donor 258 vehicle

1. Roy, are you opposed to a 4.0L swap?
2. Costs are not much more,
3. And you get fuel injection.
4. There should be plenty of 'em,
5. In wrecking yards.
6. Otherwise...
7. Almost ANY AMC product (Gremlin...etc.) had 'em.
8. I'd try to get a mid 80's block,
9. If you're intent on a 4.2L.
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post #3 of (permalink) Old 01-14-2004, 11:10 PM
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Re: 258 rebuild - best donor 258 vehicle

My $.02 says get one like I did. Look for an AMC car like the 48k grandma concorde sw that I got. You know the miles were easy on it.
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post #4 of (permalink) Old 01-14-2004, 11:20 PM Thread Starter
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Re: 258 rebuild - best donor 258 vehicle

I am just checking all of my options. Ideally I would like to have an engine ready when mine gets untolerable. Around here ragged high mileage 4.0's are going for about $700 bare with no harness or computer. I think it might be easier and cheaper to find an old 258 rebuild it in my spare time and throw a 4.0 head on it and possibly mpi or megasquirt it in the distant(years) future. If I can get a good deal on a complete low mileage 4.0 I would jump on it but they are hard to come by. I'm just trying to figure out what I am going to do because an engine rebuild or swap is definitely in my future.
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post #5 of (permalink) Old 01-15-2004, 01:15 AM
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Re: 258 rebuild - best donor 258 vehicle

Didn't they change head bolt diameter sometime on 258's? Were early or late ones bigger? What was the cut off date?
As far as I know, that and intake manifold design were the only diff on 258's through the years.
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post #6 of (permalink) Old 01-15-2004, 04:35 AM
 
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Re: 258 rebuild - best donor 258 vehicle

81-87 4.2's have the 7/16" head bolts...not a real big deal unless you want to go with a 4.0 head on it - even then you could buy a centering kit through hesco or something.... (all other 4.2's used 1/2" holes)

-p
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post #7 of (permalink) Old 01-15-2004, 06:00 AM
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Re: 258 rebuild - best donor 258 vehicle

I heard that late 258's had a different deck which will cover the water jacket holes on the right side of a 4.0 head, making that swap easier.
post #8 of (permalink) Old 01-15-2004, 07:32 AM
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Re: 258 rebuild - best donor 258 vehicle

MY .02 I can understand why you are not into going with a 4.0. Swapping Fuel injection gets pretty spendy. I think your idea of getting an old 258 and putting a 4.0 head on it is a great idea. But what about.....
Getting a 360 rebuilding that in your spare time, and putting that in when the time comes. I know that around here 360'S are usally pretty cheap. Get one from an old Waggie, scrap the motorcraft "junk" carb (i dislike motorcraft carbs) put a good 600cfm on there and get ready to rip. Around here an old "running" 360 can be had for less than a 258 or 4.0 If you are going to do a motor swap, mise well upgrade a little.
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post #9 of (permalink) Old 01-15-2004, 07:53 AM
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Re: 258 rebuild - best donor 258 vehicle

There were also some differences in crank design. The earlier cranks were heavier. Good for torque and off road.
I have a long block if you are interested. (Help to get the wife off my back about selling the Jeep [img]images/graemlins/frown.gif[/img]) It is a '72, but has never been machined. You could go .030 over and be good.
PM me if you want more info.
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