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390 engine |
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rodhhrod
AMC Addicted Joined: Jul/11/2010 Location: Oregon Status: Offline Points: 1040 |
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Posted: Oct/19/2017 at 4:55pm |
The saga continues on the 390, Question- on the drivers side the piston notches are all facing forward on the upper left about 10 oclock. The passenger side the notch are facing forward but on the lower right section about 5 o'clock. is this common or is there a screw up here. According to the TSM the notch should be upper forward. Sure could use some help here. Rod
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Online Points: 19612 |
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For a race engine 0.060" over might be okay, but thin cylinder walls mean higher temps, and a street 390/401 bored that much will likely have heating/cooling issues if driven any length of time. Not so important for drag cars -- can take time to cool between runs, and runs only last a few seconds.
jpnjim -- My best guess is the 401 as created because of competition more than anything else. Abernethey had set AMC up to compete head to head with the big three, and wanted to push AMC up into the mid priced segment (Buick/Olds/Pontiac/Mercury territory), and the competition all had 400 cubic inch engines. The upcoming changes in emissions/lower compression may have had something to do with it though, as cubic inches can make up for lower compression. |
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Frank Swygert
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70amxvegas
AMC Addicted Joined: Apr/26/2009 Location: Lost Wages Status: Offline Points: 1791 |
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60 over is ok .I bet there are a lot of them out there 60 over
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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+.060" is a lot for a 390/401,
but have the walls sonic tested before freaking out. Factory spec says +.023 max, rule of thumb says +.030" max, but others have gotten away with more +.060 = 4.225, but you don't know how thin the walls are until they're checked. You could always list it for what you have in it, hopefully the crank isn't +.030 already too ^though even then the crabk can go .050+ on the mains, and the rods can go even more depending on what you're building.
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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rodhhrod
AMC Addicted Joined: Jul/11/2010 Location: Oregon Status: Offline Points: 1040 |
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All numbers check good and it does say 390 on it. Too bad, pulled a head off yesterday and has 60 over pistons in it. So much for original, damn, not sure what I am going to do now.
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Online Points: 19612 |
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68 TSM is fine. I would check the block casting number to make sure it's a 68/69 390 though. It's old, PO may have forgot what it came from or it may have been changed before he got it. I'm assuming the side of the block has 390 cast in?
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Frank Swygert
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70amxvegas
AMC Addicted Joined: Apr/26/2009 Location: Lost Wages Status: Offline Points: 1791 |
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I will give you $801.00
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mmaher94087
AMC Addicted Joined: Apr/01/2008 Location: Arizona Status: Offline Points: 1676 |
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I used the '69 TSM to restore my '68 AMX. Other than cosmetics, everything was the same as far as I know.
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Mike
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rodhhrod
AMC Addicted Joined: Jul/11/2010 Location: Oregon Status: Offline Points: 1040 |
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Thanks all for the input. Here is the reason for asking,
I am a 70 guy so I have a 70 TSM and have access to a 69 TSM for reference. I just brought home a 390 complete motor, it supposedly came out of a 68 AMX, has everything on it except carb and air cleaner. Anyway bought it from guy from the Local AMC club that I have known for over 30 years, it has been under his work bench with the auto tranny still attached, I did not get that piece. It was a running motor when pulled, the only thing is that it is painted a orangeish red color, whick might be it has been rebuilt once before. Who knows, anyway I am going to start tearing down for inspection so I need the bore spec's to see where I am at, so would the 69 TSM work or do I need to get a 68 TSM book? Sorry for the long winded story but that is it in a nutshell. Hope I didn't pay to much for it at $800 Any thoughts? Thanks Rod |
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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Agreed. Though a less honest company could have kept calling it a 390 (like Chevy did with the 396/402) Do you think the reason for the bigger engines was to be ready for the new emissions standards and compression ratio drop after 1970/e71. I guess it could have been the trend towards bigger/heavier cars of the 1970's too. If the 304/360s seem choked off after 71, and worse so after catalytic converters in 76, imagine how they would have been without the extra torque from those longer stroke cranks. Edit, Just had a thought, Is it possible developing the new "401" camshaft is what delayed the arrival of the 401? Did late 70' 390's get the "401 cam"? (I forget now)
Edited by jpnjim - Oct/16/2017 at 6:55am |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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