AMC 258 Engine Interchange question - JeepForum.com
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post #1 of 26 Old 06-30-2010, 02:04 PM Thread Starter
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AMC 258 Engine Interchange question

I am about to start my swap from a 1985 engine that has a knock, to a 1979 long block that reportedly runs perfect. Does anyone have any suggestions or knowledge about obstacles I may run into, or is the block & head completely interchangeable with the later model?

I was going to run the 1979 engine with a clifford intake, holley carb, etc but have decided to keep the computer controlled junk & carb until I can switch over to fuel injection.

Anyways, I believe the two engines are identical but have seen some bizarre part number cut offs around 1980 - maybe this is just for the passenger car engines?

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post #2 of 26 Old 06-30-2010, 06:16 PM
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Your 79 Head bolts wont fit you 85 head
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post #3 of 26 Old 06-30-2010, 06:22 PM
crzdmnky
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Originally Posted by 1986cj View Post
Your 79 Head bolts wont fit you 85 head
I agree with this. Plus I think they changed some other things in the newer 258 engines to give them more horsepower.
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post #4 of 26 Old 06-30-2010, 06:29 PM
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It also might be an issue for insurance if you are swapping in an older engine than that of the original Jeep. Regardless, with all the time and expense that goes into an engine swap, wouldn't it be better to get some better technology out of the deal (more horses couldn't hurt either right?).............?
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post #5 of 26 Old 06-30-2010, 07:19 PM Thread Starter
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Originally Posted by Ben_88Jeep View Post
It also might be an issue for insurance if you are swapping in an older engine than that of the original Jeep. Regardless, with all the time and expense that goes into an engine swap, wouldn't it be better to get some better technology out of the deal (more horses couldn't hurt either right?).............?
Yes you are so right you don't even know. I would be thrilled to do a vortec swap but the timing doesn't seem right. I have found engines for just $500 on craigslist, and I do have my sm420 swap ready to go ...

I also doubt I can sell the 1979 motor for what I got in it, maybe part it out?

As for the head bolts, this echoes what i`ve heard from someone else too.
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post #6 of 26 Old 06-30-2010, 07:20 PM Thread Starter
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I would like to add also, someone told me from experience that he had his head bolt holes reamed out on an 80's head, and it bumped his compression when put on his 70's shortblock.
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post #7 of 26 Old 06-30-2010, 07:22 PM Thread Starter
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Maybe I should diagnose and fix my knock until I can perform a v8 swap? lol
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post #8 of 26 Old 06-30-2010, 07:33 PM
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Quote:
Originally Posted by Ben_88Jeep View Post
It also might be an issue for insurance if you are swapping in an older engine than that of the original Jeep. Regardless, with all the time and expense that goes into an engine swap, wouldn't it be better to get some better technology out of the deal (more horses couldn't hurt either right?).............?
The time and expense involved in this particular swap is minimal....especially if the 79 engine is a complete long block as mentioned (Head bolts wouldn't be an issue then either). If its just to have a driveable Jeep go for it...all it'll cost you is time.

'84 CJ-7: Yota axles (spartan locked front, e-locked rear) 4" BDS, 1" Daystar & 3/8" shackle lifts, 35" X-Terrains on steelies, YJ Tub & family roll bar, heater blower upgrade, 4.2L w/MC2100 & Team Rush, Warn 8274. Rebuilt 4.2/4.0 hybrid, AX15 and twin sticks/clocking ring waiting to go in.

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post #9 of 26 Old 06-30-2010, 07:46 PM Thread Starter
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Originally Posted by jeepwhore View Post
The time and expense involved in this particular swap is minimal....especially if the 79 engine is a complete long block as mentioned (Head bolts wouldn't be an issue then either). If its just to have a driveable Jeep go for it...all it'll cost you is time.
Yes that is the goal - driveable til I collect parts for a "real" swap - time and etc is no problem, i`ve done these a few times on junk jeeps i`ve bought - my biggest question was about using my later model intake, etc to get it running.

I did go out there and visually compare the bolts between the two engines - size looks identical, i`m really not sure which direction to go!

lol thanks for all the info
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post #10 of 26 Old 06-30-2010, 08:58 PM
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Externally, the motor mounts are the same. Same with the bell housing pattern(as well as the AMC V8s.) I removed my 258 and I'm dropping a AMC 360 between the frame rails. Basically a bolt in V8 swap.
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post #11 of 26 Old 06-30-2010, 09:26 PM Thread Starter
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Externally, the motor mounts are the same. Same with the bell housing pattern(as well as the AMC V8s.) I removed my 258 and I'm dropping a AMC 360 between the frame rails. Basically a bolt in V8 swap.
That is a cool way to go, and plenty of those motors to be found around here.
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post #12 of 26 Old 07-01-2010, 08:18 PM Thread Starter
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So, this weekend i`m going to go the logical route and see if I can diagnose this knock - maybe i`ll get lucky and just have a broken spring or other valve train sort of issue.

If anyone has any further suggestions i`m all ears. I got the stethoscope, pull the plug wires to check for wrist pins and some very basics like that but i`m a total newb to this sort of engine diagnosis.
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post #13 of 26 Old 07-01-2010, 08:28 PM
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Knocks could be alot of problems, its no fun chasing them things down, especially when you find out its in the bottom end of the engine. Is it a bad knock? My old 83' engine knocked like a son of a gun, but still ran awesome and didnt use oil. It had low oil pressure, so it could of been the pump knocking or to much clearance between the crank and bearings.
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post #14 of 26 Old 07-01-2010, 09:39 PM
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I put an '86 head on my '74 block a yr. ago or so. The combustion chamber on the later head is smaller and the '86 pistons were concave with a compression ratio of 9.2 to 1. The older engine had flat top pistons at about 8 or 8.4 to 1. There was no problem with valve clearance but I did use '86 push rods.
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post #15 of 26 Old 07-01-2010, 10:15 PM Thread Starter
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Quote:
Originally Posted by crzdmnky View Post
Knocks could be alot of problems, its no fun chasing them things down, especially when you find out its in the bottom end of the engine. Is it a bad knock? My old 83' engine knocked like a son of a gun, but still ran awesome and didnt use oil. It had low oil pressure, so it could of been the pump knocking or to much clearance between the crank and bearings.
The previous owner told me he drove this thing for many miles with the knock and had no major problems - it also does not burn oil and everything looks really good. He also added an HEI distributor which was after the knock was discovered. As for how bad it is, seems more like a tap and really reminds me of an exhaust leak I had on a v8 before. I will pull the valve cover first and see if anything is obvious. Oil pressure seemed to be around 35 psi last time I started it - again more things I need to look closer at.


Quote:
Originally Posted by CJ258 View Post
I put an '86 head on my '74 block a yr. ago or so. The combustion chamber on the later head is smaller and the '86 pistons were concave with a compression ratio of 9.2 to 1. The older engine had flat top pistons at about 8 or 8.4 to 1. There was no problem with valve clearance but I did use '86 push rods.
Nice this is what I have heard before as well - and this could very well be the direction I take - i`m not clear if the carter garbage will work with the compression change but I am sure it would be fine.
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