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  #1  
Old 01-06-2018, 08:08 PM
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Head Swap

Will 3212993 Heads Late 71 Fit on a 88 360 Block
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  #2  
Old 01-09-2018, 08:21 PM
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  #3  
Old 01-10-2018, 04:03 AM
wiley-moeracing wiley-moeracing is offline
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I forget but when did they swap from 7/16 head bolts to 1/2 inch?
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Old 01-10-2018, 09:04 AM
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My '72 has 993 heads and they use 1/2 inch bolts. Verify that all the holes you need for mounting things are there. Mine have one less tapped hole than later heads. The hole would be on the front if the head is mounted on the right. I think maybe for the A/C pump mount? It would be on the back if mounted on the left. I have no idea what was mounted there on later models.

Last edited by Crankyolman : 01-10-2018 at 09:35 AM.
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Old 01-10-2018, 10:03 AM
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Only issue may be accessory bolt holes.
Early vs. late use different thread sizes.
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  #6  
Old 01-10-2018, 10:59 AM
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Head bolts changed with the 1970 model year.
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Old 01-12-2018, 12:36 PM
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I had a 71 401 w/ 7/16 in head bolts....Not saying it wasn't built in 70 though I guess.

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Old 01-12-2018, 04:46 PM
440sixpack 440sixpack is offline
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If there was a 7/16 401 it had to be a prototype or something. the early '71 401's had the same heads as the '70 390 and then they went low compression mid '71 model year . but all 401's were made in late 70 on so they should have had 1/2" bolts.

1970 is also when the intake bolts went from straight to staggered.
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Old 01-12-2018, 07:28 PM
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I've read of other 401s with 7/16" bolts, I believe they were service replacement blocks which were intended to be machined to whatever size necessary and somehow failed to get the head bolt holes sized to 1/2".
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Old 01-12-2018, 08:11 PM
440sixpack 440sixpack is offline
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That could be possible. it would be interesting to know if they had 401 cast in them or the correct part number . I suppose there is a possibility the 401's AMC sold IH could be different in ways like this. I've never looked at one.

I guess on a Jeep who cares about originality but on an AMX nobody would buy it.
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Old 01-12-2018, 09:29 PM
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Quote:
Originally Posted by 440sixpack
That could be possible. it would be interesting to know if they had 401 cast in them or the correct part number . I suppose there is a possibility the 401's AMC sold IH could be different in ways like this. I've never looked at one.

I guess on a Jeep who cares about originality but on an AMX nobody would buy it.
All the service blocks had the 401 part number but the 401 cast under the motor mounts was filled when cast or ground off. I understand there is usually a faint impression of it on most of them. They are actually fairly desirable blocks because often they are undersized because the blocks were used for every engine size.

Last edited by Crankyolman : 01-12-2018 at 09:34 PM.
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Old 01-13-2018, 05:58 AM
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Mine was a service block or crate motor. The 401 had been ground off and the crank was not machined for an auto trans.
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Old 01-13-2018, 11:20 AM
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Still wouldn't explain the 7/16" head bolts though. no 401's were made prior to 1970 so this doesn't add up.

Unless the service blocks were tapped for 7/16 so they could be used on 68-69 vehicles as well.

None of this matters at all. but it's interesting nevertheless.
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Old 01-13-2018, 02:32 PM
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I ended up discussing w/ American performance products in Fla....They seemed to have decent info but yes,,,,still doesn't really explain it. He just knew I had a crate motor...

Said it was a 71 and that they were sold out west particularly to be used for things like pumps and generators.
https://www.amclives.com/

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  #15  
Old 01-13-2018, 09:08 PM
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My understanding is the service blocks were used as warranty replacements for all AMC V8s so they were actually made with the 7/16 bolt holes which were to be stepped up if replacing a post 70 engine but on occasion that didn't happen. As I said they weren't bored to size either because they might have been used to replace a 343, 360, 390 or 401, I'm not sure if they were undersized enough to do the smaller v8s but I think I remember reading that they were. This is how a block with 401 part number could wind up with 7/16 bolts. It may actually be any size engine, which can't be determined without taking one apart and measuring, and may have originally replaced a pre 70 engine or someone just missed stepping up the holes to 1/2".

You are correct that it doesn't rely matter other than I find it an interesting fact that there are a few 401s out there with service blocks that do have the 7/16" head bolts.
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Old 01-13-2018, 10:26 PM
440sixpack 440sixpack is offline
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I would hazard to guess they came with a 360 bore and you could bore it to 401 if desired.

You could of course bolt any post '70 heads on with 7/16 bolts so it would make sense they come set up for the smaller bolt size. and if you had a 69 or older set of heads you could just bolt the new block under them and reinstall your old style intake and rectangle port exhaust manifolds and you're done.
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  #17  
Old Today, 02:15 PM
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I think the Service Replacement blocks also had enough meat in the main bearing webs that you could machine them for a 4 bolt main cap but good luck finding a set of those caps anymore.
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  #18  
Old Today, 02:34 PM
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Quote:
Originally Posted by wiley-moeracing
I forget but when did they swap from 7/16 head bolts to 1/2 inch?
1970 and up have 1/2" head bolts

I have never seen a 401 with 7/16" head bolts including service blocks or the Binder (IH) blocks. The 1968 and 1969 390 blocks did have 7/16" head bolts.
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