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Engine Selection: What To Do?

Discussion in 'Intermediate CJ-5/6/7/8' started by DHill78, Jan 13, 2017.

  1. Jan 13, 2017
    DHill78

    DHill78 Sponsor

    Central AR
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    A little history first. 72 CJ5. Came factory with 304, but PO, or actually the guy before PO, installed a 401. It wasn't running when I bought it, had been sitting in his garage for 17 years. I got it running and had good power but smoked like freight train.

    I didn't do a leak down, or compression test. Just decided I was going to rebuild it. Pulled the engine and tore it down over Christmas/New Years, and carried it to our local machine shop.

    Bad news...crank needs turned on mains, rod journals just need polished. Block has been bored .060" over already. They said there's not enough wall to bore anymore.

    So here's my question: Should I search for a 304? Or find a I6? Or a 360? I've found a good buildable 360 already. The others may be harder to find.

    I'm not looking to build a crawler, or hot rod, or anything special. Will mainly just be used to cruise around in, and very light trails. This is what makes me lean toward the I6, but I'm also afraid I'll miss the power.

    Thoughts?
     
  2. Jan 13, 2017
    DrDanteIII

    DrDanteIII Master Procrastinator

    Milford NJ 08848
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    The 401 might still be worth something the AMC hot-rod crowd. (No really, they exist) So maybe selling it can offset the cost of your next steps.

    Since you're already set up for a V8, the 360 would be the way to go. Plentiful on the second hand market, and lots of parts available. Just know that you will need your flywheel re-balanced between the 401 and 306 (and 304 for that matter).

    You could also put the 401 crank and rods into the 360 block and end up with a 385.

    And if you like building hot rod motors then you bore the 360 out for chevy 400 pistons and end up with 393ci.
     
  3. Jan 13, 2017
    rejeep

    rejeep Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Rochester, NY
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    agree...
    put the 401 in the hand of somebody who wants a 401...
     
  4. Jan 13, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    I don't see any advantage to a 304 over a 360 if you don't have one now. You can put the 401 crank in a 360 block and get a 385 engine. The steel crank is worth saving, but fixing a 60-over 401 block would probably cost a grand for sleeves. Last I heard, sleeves were about $100 per hole.

    If you want to go with an inline, the Jeep 4.0L either in the early Renix form or the later HO form (with its excellent Mopar MPI) would work well. This would not be as easy as the 304/360/401, which would be a drop-in change with the right flywheel. Changing to a six will need different frame towers, different driveshaft lengths, other stuff like a different radiator... not hard but more work than the AMC V8.

    A modern MPI Chevy would be another option, with either the original T-15, a truck 4-speed or even an automatic. Of course, this would be more work.
     
  5. Jan 13, 2017
    47v6

    47v6 junk wrecker! 2023 Sponsor 2022 Sponsor

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    These options sound pretty exciting to me. Keep us posted.
     
  6. Jan 13, 2017
    DHill78

    DHill78 Sponsor

    Central AR
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    I've been reading some on an amc forum also. I will probably try to sell the engine (part or whole) on that forum. The crank and rods are still worth something, and the block may be to the right person. Evidently, the earlier blocks (cast with CFD in the valley) are the earlier ones, which is what mine is.

    The 360 I have access to has a flywheel with it, so I will use it, (if I go that route) and will also stick with the 360 crank.
     
  7. Jan 13, 2017
    DHill78

    DHill78 Sponsor

    Central AR
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    I started a build thread a little over a year ago, but I haven't really done much to it besides drive it around until recently. I usually drove it at night so I couldn't see all the smoke! :rofl: But I finally decided if I didn't get started working on it, I wouldn't ever get it done. So I tore it apart when I had some time off work over the holidays. Time is my biggest hold up...of course finances run a close second.

    I will try to keep the build thread updated with photos.
     
  8. Jan 13, 2017
    DHill78

    DHill78 Sponsor

    Central AR
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    I really would like to hear some more thoughts on the I6. I want to keep it as stock as possible, so I'm not really even looking in to a later model engine. This may be a mistake, but I will probably stick with a carbureted engine for now.

    My dad had a 72cj when I was growing up. 258 I6, T18. With mine being a T15, is the 258 a good option? Or will I miss the low gear?
     
  9. Jan 13, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Regarding the good build-able 360, realize that there are a lot of these engines around, and many of them have high miles. The AMC V8s can have low hot idle oil pressure at high miles, typically due to a worn oil pump (in the aluminum timing cover) or delaminated camshaft bearings. A hammered rod bearing seems to be the most common catastrophic failure for these engines, likely resulting from normal bearing wear combined with the low hot idle oil pressure. Of course, poor maintenance will accelerate this process.

    Just be aware if you are searching for a runner.
     
    Last edited: Jan 14, 2017
  10. Jan 13, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    You'd be fine with a 258 and the T-15. My J10 has that combination and does fine ... even with more weight and taller gears than a CJ. A T-15 has a 3:1 first, and the close ratio T-18 supplied with a '72 CJ has a 3.09:1 second, which is the gear you'd start off in. The 258 has a long stroke for its displacement, meaning the torque peaks at a fairly low RPM (ca 2000). This means the engine is limited on power, since power is torque times RPM and the torque starts to fall off at a fairly low speed. But the AMC 6s are really great engines, especially the pre-1981 examples ... smooth, durable, reliable, no obvious mechanical faults. If you want more power for the highway, the 4.0L engines (242 ci) are a shorter stroke, bigger bore, higher compression, more powerful version of the '81-up 258. They can be carbureted if you must have a carburetor.
     
  11. Jan 13, 2017
    fhoehle

    fhoehle Sponsor

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    I have had great luck with 258s thru the years but if I had a 360, I would just give it a freshening up rebuild and stick that in.
     
  12. Jan 13, 2017
    Rich M.

    Rich M. Shoe salesman 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Gotta ask even at 60 over can it just be honed? Lots of reasons for smoke and if the cylinders aren't out of round it may be salvageable. Ime a 258 with mild cam Clifford intake and header can smoke a 304
     
  13. Jan 13, 2017
    DHill78

    DHill78 Sponsor

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    The machine shop did mention this as an option. Said there wasn't a ring groove, and he could probably hone it and it work out fine. I'm just not sure I would trust it.
     
  14. Jan 13, 2017
    47v6

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    I would do it if they offered this option. They know if a hone will work or not.
     
  15. Jan 13, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    The original cylinder wall thickness is really thin on a 401, and 60 over is too much for many (most?) 401 blocks. AMC specifies something like 30 over maximum, although some blocks can go 60 over, if the core shift is minimal. The core shift must be sonic tested prior to machining. 401s with significant core shift will overheat when bored 60 thou, since the thin spots in the cylinder walls conduct too much combustion heat to the coolant.

    The other engines mentioned (304, 360, 258, 4.0L) are all conventional gray iron blocks and can be bored twice, typically at 30 and 60 over. It is possible for these blocks to be bored beyond 60, if they are sonic checked and core shift is minimal.

    JMO - all 401 blocks should be sonic checked before any overbore, and I would sonic check a gray iron block before I went 60 over. Easy, inexpensive test.

    Your machinist should know about this.
     
    Last edited: Jan 14, 2017
  16. Jan 14, 2017
    4wealn

    4wealn Member

    Ontario, Canada
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    Don't be afraid to switch over to a fuel injected 4.0. My 74 originally had a 258 mated to a T-14 which I had swapped out for a T-15 and now swapping out for a T-18 lol and it is bolted to a 98 TJ 4.0. It is really a bolt in. All you will need is the motor mount brackets for the I6. The bellhousing from the T-15 will bolt right up, all the factory mounts work for the crossmember. I did not have to change or drill anything.
    The fuel injection is great for off road.
    There are two main items that will need to be addressed. First you will either have to get the bellhousing machined for the CPS (what I did), or buy the hesco kit that puts it on the balancer, and secondly you will have to lean out the wiring harness and keep only the wires you need to allow the motor to run. If you do not feel comfortable doing this than it can be sent to hot wire auto, I have heard numerous times they do a great job.

    Please don't hesitate to ask me any questions if you decide to go this way.
     
  17. Jan 25, 2017
    DHill78

    DHill78 Sponsor

    Central AR
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    I've made up my mind... This is the route I'm going. Mainly because it's what I already have, and the engine shop said it would work fine. He called today, and I went over there to look. He showed me the #5 piston was burned up and the rings were broke. Said it probably got very hot at some point. (But this makes since, as it smoked from the left exhaust).

    He honed it out, and was pleased with the results. So, in the near future, I will have it back and start putting this thing back together.
     
    73 cj5 likes this.
  18. Jan 25, 2017
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    :)

    H.
     
  19. Jan 26, 2017
    fhoehle

    fhoehle Sponsor

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    401s do run hot, but they do run strong. Get yourself a good aluminum radiator and a non clutch rigid mechanical fan with lots of blades and a good shroud. I bet you will be ok then.
     
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