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  1. #1
    Join Date
    Jan 2005
    Location
    Arkansas
    Posts
    17

    Default AMX engine components

    Hi all, another noob here. I am restoring my 69 AMX that I have had for about 20 years. I have been working on it on and off for the past few years and am ready to start on the engine. I want to use the later model dogleg port heads on the 69 390 block and would like to know what machine work is involved in doing this. I have a set of heads, but don't know the specs on them or what engine they came from. I dry fitted them this afternoon just to see how close everything lined up and they seem to look OK except that the front and rear seal gap btwn the intake manifold and block looks a little wide. The locating bushings are a different size too, apparently for the later model 1/2" head bolts but that is manageable. I was told once that the deck height was different on 70 and up engines but don't have any real data to go on. What needs to be done to the heads or block if anything?

    Barron

  2. #2

    Default

    Hi Barron and welcome!

    The 1969 and prior V-8 head bolts are 7/16", 1970 and later are 1/2".

    What you'll need to install the dogleg heads on your '69 390 is four "step-dowels". You can buy these from American Performance Products in Florida (do a Google, I don't have their # handy or try your favorite AMC vendor). Then you'll want to buy a new set of head gaskets for the 1970-up AMC 401 V-8. Copper Coat one side and drop the heads onto your 1969 390 block and torque them to 105 lbs/feet. There is no machining needed to do this, it is a simple drop-on. The deck height differences between the earlier and later V-8 blocks are in the block, not the heads.

    Be certain to use a 1970 and later intake manifold - whether it's an aftermarket or stock. There is a slightly different bolt pattern (center holes only) between the intake holes on a 1969 and prior head and intake and the 1970 and later. Don't hog out the holes on the 1969 and prior intakes.

    Use Permatex/Aviation Form-A-Gasket #2 non-hardening to seal the ends of the intake manifold, especially around the water jacket areas. DON'T USE SILICONE, black or blue or any other color.

    Use stainless steel valves in place of the earlier valves. Use for both the intake and exhaust valves. Because AMC used a high nickel content in the block and heads (which makes the heads and blocks hard enough to start with) hardened seats are redundant and are a waste of money on any AMC V-8.

    If you're planning on using stock exhaust manifolds you'll want to get a pair of the 70 and later Free-Flow manifolds, preferably without the tubes.

    One other thing; The 68/69 390s had a 10.2:1 compression ratio. The larger chambers on the later 58cc heads will drop your compression ratio to approximately 9.6:1. Not a bad thing on today's gas, though you'll still want to use octane boost.





  3. #3
    Join Date
    Jan 2005
    Location
    Arkansas
    Posts
    17

    Default

    Thanks for the info. This is a great resource.
    How can I tell what kind of heads I have? Are there some that are not worth putting on the 390. These heads could have come from a 304 for all I know. I want to be sure they are better than the older head
    I am also putting a 727 behind it so I will have to have the Crankshaft machined out as well. Do you know where I can find the right sleeve/bushing where the torque convereter fits?

    Barron

  4. #4

    Cool Heads and all sort of things

    The heads from a 304 has smaller valves on them. I am not sure of the inch diameter, but I know the valves themselves are smaller. This info could be found in any pre 75 shop manual (ie. Chiltons, Peterson's etc.). The other place is in the AMC shop manual if you are lucky to have one. On the 390's I believe the intake valve size is like 2.02" and the exhaust is 1.75" although I am not real sure on that number since my shop manual is at work and not here, I try to remember to look it up and get back to you tomorrow on it. Otherwise have fun and will write later

    Note: Do not attempt to install 304 heads on your 390 engine. I do not beleive they will fit anyway. Just an after thought. Besides with smaller valves, you would be much better off finding any set of heads 360 CI or bigger. The 360,390, and 401 heads are basically the same with the 304 and 290 being different in the aspect ofthe valves
    Last edited by donsjave; 01-11-2005 at 06:13 PM. Reason: 304 heads not worth the bother

  5. #5
    Join Date
    Jan 2005
    Location
    Arkansas
    Posts
    17

    Default Head stuff

    I had a look a them last nght. The valves are, Intake approx 2.03 and Exhaust approx 1.67. The valves are still installed and that was as close as I could get. Not much room to expand. Sounds like they may be 390 heads. I have the AMC part of a very old Chiltons manual but the valve diameters are not given, just everything else.
    The 2 center holes on the intake manifold aren't even close. I wouldn't consider opening them up. I'll look for a 70 model. Probably go with an aftermarket.
    Looks like I'm ready for the machine shop.

    Barron

  6. #6

    Default

    Just an FYI: Ye old AMC Service Spec books show the '70 360 and 390 valves to be:
    Intake = 2.025"
    Exhaust = 1.625"

    The '70 304 valves are:
    Intake = 1.787"
    Exhaust = 1.406"





  7. #7

    Default Heads

    Quote Originally Posted by Barron
    Hi all, another noob here. I am restoring my 69 AMX that I have had for about 20 years. I have been working on it on and off for the past few years and am ready to start on the engine. I want to use the later model dogleg port heads on the 69 390 block and would like to know what machine work is involved in doing this. I have a set of heads, but don't know the specs on them or what engine they came from. I dry fitted them this afternoon just to see how close everything lined up and they seem to look OK except that the front and rear seal gap btwn the intake manifold and block looks a little wide. The locating bushings are a different size too, apparently for the later model 1/2" head bolts but that is manageable. I was told once that the deck height was different on 70 and up engines but don't have any real data to go on. What needs to be done to the heads or block if anything?

    Barron
    DONT BOTHER THE DOG LEG HEADS ARE NOT AS GOOD AS THE EARLY HEADS.IF YOU HAVE ANY QUESTIONS YOU CAN GET ME AT FASTESTAMX@AOL.COM
    JOHN

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