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  #1  
Old 10-03-2018, 11:01 PM
mattmopar440's Avatar
mattmopar440 mattmopar440 is offline
AMC 4 OH! 1
 
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258 Years

So I got a new rig and the 258 is Very tired it an 1984 and has a serpentine belt does anyone know the years in the motor difference Im looking for a 77 as a replacement
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80's J10 258/T-5/208
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Originally Posted by Heavy_Metal_Thunder_81
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Old 10-03-2018, 11:50 PM
joe joe is offline
 
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Don't know about all the 258 changes but a big change came in 81 with smaller size head bolts along with the related head difference and the new stock plastic valve cover/mounting. In 83 the 258 in FSJ's went crazy with vac/elec smog switches. My 83 Chero eng bay was a hose/wiring bowl of spaghetti from hell. I have no idea when the serpentine belt thing started. My 83 FSJ didn't have it nor did an 84 258 I pulled from a bone stock 84 CJ. I'm sure there were other changes but the blocks eng mount location and AMC bolt pattern didn't change between 77 and the last year of the 258 in 87 so a 77 will at least drop/bolt into an 84. Doan know about the externals compatibility though?
Hopefully others can add to this.
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  #3  
Old 10-04-2018, 01:10 AM
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FSJunkie FSJunkie is offline
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The 258 can basically be split into three generations.

Generation 1: 1971 only

1/2" head bolts. 12 counterweight crankshaft. Cast iron intake and exhaust manifolds. 8.0:1 compression ratio. Carter YF 1bbl carburetor. 150 gross (roughly 110 net) horsepower. Bell housing to match to Borg Warner automatic transmissions.

Generation 2: 1972-1981

Bell housing changed to match the Chrysler Torque-Flite automatic transmissions. Minor changes to fuel and ignition systems. Blocks starting in 1980 added a mounting boss on the driver's side for the Eagle front drive axle. People are going to say I'm full of BS for this, but the 1bbl 258 remained around 150 gross / 110 net horsepower during this time despite emission control additions. An optional Carter BBD 2bbl carburetor was introduced around 1976 and produced around 160 gross / 115 net horsepower.


Generation 3: 1982-1991

Block lightened. Cylinder head casting altered. Head bolts reduced in size to 7/16". Crankshaft reduced to 4 counterweights. Aluminum intake manifold and tubular style exhaust header. Plastic valve cover. Compression ratio raised to 9.2:1. Computer engine control system. I'll get called a liar for this too: roughly 165 gross / 120 net horsepower.


The Generation 3 engines are not that bad to figure out. I rebuilt the 258 in my 1984 Eagle myself. It's only "spaghetti" if you don't know what everything does. Get a actual AMC factory service manual, read it, study the vacuum diagram, and figure out how it all works. The individual systems are not that complicated just there are a lot of systems. Doesn't take a rocket scientist to figure them out. People are just lazy and don't want to put in the effort to study and learn. It only becomes spaghetti if you are trying to figure it out on your own without a service manual or if somebody before you started mixing up hoses and unbundling things. If you just go through it all end to end and bundle the lines together in an organized fastion with zip ties it's not bad at all. The biggest problem is the vacuum lines dereriorate or people start plugging things. Then the computer freaks out and throws the fuel mixture way off.....then the owner nutter bypasses as a last resort. Keep it all working like it should and they run extremely well. That is the advice an actual retired AMC service technician gave me and it has treated me very well.
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  #4  
Old 10-04-2018, 06:13 AM
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tgreese tgreese is offline
 
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Quote:
Originally Posted by mattmopar440
So I got a new rig and the 258 is Very tired it an 1984 and has a serpentine belt does anyone know the years in the motor difference Im looking for a 77 as a replacement
I'm surprised that an '84 would get the serpentine belt. Looks like '83 was the first year for a serpentine belt but only in some models. 1977 was the first year for the 2 barrel iron intake manifold, used with a mechanical Carter BBD carb (no "computer controlled" stepper motor, as in 1984), but only in the FSJs; the CJs in 1977 still got the 1V YF and the 1V iron manifolds. A '77 uses all V-belts. All this stuff should be interchangeable between blocks as long as you take all of it from one year or the other.
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Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
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  #5  
Old 10-04-2018, 11:55 AM
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mwood65 mwood65 is offline
232 I6
 
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Crankshaft

It went from a 12 counterweight crank to a 4 counterweight?!?
That seems like quite a change.


So are the Gen 3 crankshafts less strong or reliable over the long haul or in a stock engine are they still fine?


I have the original engine in my 74' Cherokee so I guess that would be a Gen 2.
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  #6  
Old 10-04-2018, 12:07 PM
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mattmopar440 mattmopar440 is offline
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Quote:
Originally Posted by tgreese
I'm surprised that an '84 would get the serpentine belt. Looks like '83 was the first year for a serpentine belt but only in some models. 1977 was the first year for the 2 barrel iron intake manifold, used with a mechanical Carter BBD carb (no "computer controlled" stepper motor, as in 1984), but only in the FSJs; the CJs in 1977 still got the 1V YF and the 1V iron manifolds. A '77 uses all V-belts. All this stuff should be interchangeable between blocks as long as you take all of it from one year or the other.

its a Californian rig with AC so not sure what changes it had over the rest of america
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80's J10 258/T-5/208
89' Jeep GrandWagoneer
New Project
74' J10 Go Grabber Green Running
Quote:
Originally Posted by Heavy_Metal_Thunder_81
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  #7  
Old 10-04-2018, 01:12 PM
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FSJunkie FSJunkie is offline
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Quote:
Originally Posted by mwood65
It went from a 12 counterweight crank to a 4 counterweight?!?
That seems like quite a change.


So are the Gen 3 crankshafts less strong or reliable over the long haul or in a stock engine are they still fine?

The original 1964 SAE engineering development paper for the AMC 199 and 232 sixes talks a lot about crankshaft development. The first crank they designed for these engines was a 4-counterweight design that performed to all expectations except for smoothness. It could not match the smoothness of an 8 or 12 counterweight crank. So, production 199-232 engines got an 8-counterweight crank. The 258 came along later and received the 12-counterweight crank because of it's longer stroke and greater imbalance caused by it.

The higher counterweight crankshafts are not necessarily stronger. They are smoother and produce longer main bearing life. All the cranks are in perfect dynamic balance. An I6 crank actually achieves dynamic balance without any counterweights. The trouble is that as it spins faster, the mass of each crank pin starts to bend the crank, which throws it out of balance and loads the bearings. A few large counterweights (4) prevents most of this. Many small counterweights (8 or 12) eliminates it.


I don't like the idea of the long stroke 258 with only 4 counterweights, but it actually works pretty well. My 1984 258 has this crank and I rebuilt it for the first time at 170,000 miles. The crank and bearings were in such good shape that all I did to it was polish the crank and install new standard size bearings. There was virtually no wear on the crank, so standard size bearings fit to proper clearance. It actually had less wear on it's crank and bearings than my 1977 232 with the 8-counterweight crank had at 60,000 miles less. That being said, the 1984 258 is not quite as smooth and has a lower redline of 4500 RPM. The 4-counterweight 258 crank is the crank usually used when people build 4.6L strokers of over 300 horsepower, so you know it can handle some abuse. It just makes a little more vibration and may need slightly heavier duty bearings since it does load the bearings more.
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  #8  
Old 10-04-2018, 01:33 PM
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Cecil14 Cecil14 is offline
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Quote:
Originally Posted by FSJunkie
The 4-counterweight 258 crank is the crank usually used when people build 4.6L strokers of over 300 horsepower, so you know it can handle some abuse.

This is news to me, I've never seen anyone recommend the 4 counterweight crank in all of my stroker wanderings. No one generally claims it is bad either, but the recommendation I have always seen is the 12 counterweight crank.

That being said, I have never, that I can recall, seen an instance of a broken 258 crank. I've seen people claim stock cranks capable of 600+ hp numbers. For a long time there simply were no forged cranks available. I looked when I built my last motor about 10 years ago, and they just didn't exist. There are some out there now, though.


aa
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  #9  
Old 10-04-2018, 03:51 PM
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tgreese tgreese is offline
 
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Quote:
Originally Posted by mwood65
It went from a 12 counterweight crank to a 4 counterweight?!?
That seems like quite a change.
...
My understanding is that all the changes to the engine in '82 reduced the total engine weight by 85 lbs. (This is the number I have heard, don't know if it's correct.) Aluminum intake manifold, thinner, smoother exhaust manifold, thinner block casting (advances in casting tech), fewer crank counterweights, plastic valve cover - all saved weight. The 258 was not outrageously heavy already, said to be about 50 lbs lighter than contemporary AMC V8s.

It's true that builders would seek out the early crank for stroker motors. Last I read they are getting harder to source, and builders are reluctantly using the later cranks ... to no great difference it seems.
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Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
ECO Green: '15 FCA Jeep Cherokee KL Trailhawk
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  #10  
Old 10-04-2018, 05:02 PM
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Cecil14 Cecil14 is offline
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I've built strokers with both cranks, and honestly I didn't notice a bit of difference. I would guess the heavier crank would make a bit more low end torque, as well as revving a bit lower in general (think harder to stall). The lighter crank would, likewise, probably rev a bit better up top and push the powerband up a few hundred RPMs. Honestly, probably unnoticeable without a dyno.


aa
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