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V8 head bolt question

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Category: The Garage
Forum Name: AMC V8 Engine Repair and Modifications
Forum Description: AMC-made V8 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: https://theamcforum.com/forum/forum_posts.asp?TID=11676
Printed Date: Mar/28/2024 at 3:19pm
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Topic: V8 head bolt question
Posted By: billd
Subject: V8 head bolt question
Date Posted: Jul/09/2009 at 7:30pm
The head of the local MOPAR club directed a fellow to me today - this fellow has a 77 Hornet that someone put a 290 in.
As he was putting the heads back on it, he broke a head bolt. Ouch, he got the piece out.
He's tried to find new bolts locally and the local Jeep place literally laughed at him and said they were sorry he had an AMC and could not help him. (Stew Hansons, don't ever go there anyway)
I was wondering - is there a chance that Jeep dealers may still have head bolts for the AMC V8, and if so, can I get a number?
Otherwise, if I could get him a few good used bolts to get him back on the road (I can tell he's a Rambler person, trying to get it running cheap and by himself)
I did help him a lot by explaining that you don't adjust the valves like a chevy - my first clue that he may have been trying that was he commented about the valves being loose and he tried to adjust a couple and said "they have the rockers like the chevrolets did".
I said it may look that way, but.........
I also suspect his issue is a bad cam, but that's another thing.
Any ideas on him getting head bolts locally?


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Replies:
Posted By: poormansMACHINE
Date Posted: Jul/09/2009 at 7:48pm
You're talking 7/16 head bolts, not the later 1/2".


Posted By: billd
Date Posted: Jul/09/2009 at 7:57pm
I thought the 290 might be different, couldn't recall.......... been a while since I worked on my brothers 69.
He thought it was a 304, I said it was really easy to tell - crawl under it.. etc.
He then said, oh, then for sure it's a 290. (he already looked under the car)


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Posted By: bigbad69
Date Posted: Jul/09/2009 at 8:07pm
290 would be 7/16" bolts.

I broke a bolt putting my engine back together too. Ended up buying a set of ARP bolts. No worries about breaking them!


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69 Javelin SST BBO 390 T10


Posted By: TorqueyAMX
Date Posted: Jul/09/2009 at 8:10pm
The simplest solution would be ordering ARP Bolts from ARP, Summit Racing or whatever.

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Posted By: billd
Date Posted: Jul/09/2009 at 9:30pm
That's what I suggested, he was familiar with JEGS, SUMMIT, etc - but I suspect money is a real issue, a fellow a bit older than myself, and the location he said he lived indicated not a high-income area.
I said I'd try to help - so that's what I'll do!
I wish I had some spares here, I'd run them over to him.............


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Posted By: d7javelin
Date Posted: Jul/09/2009 at 11:15pm
Dorman makes head bolts.  I bought a set of 1/2 inch bolts in case I ever needed them.  The catalog had no listing for AMC but, the buyers guide listed the bolts by sizes.  As it turns out, the AMC head bolts and Olds head bolts were the same.


Posted By: r08ert209cali
Date Posted: Jul/10/2009 at 4:07am
pm me I can send you some used bolts off my 304


Posted By: farna
Date Posted: Jul/10/2009 at 8:43pm
A grade 8 bolt from the local fastener supply should be fine, same length and all. 

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Frank Swygert


Posted By: BassBoat
Date Posted: Jul/11/2009 at 8:47am
The torque specs for a grade 8 bolt are less than the stock head bolts, so my interpretation is that the stock head bolts are stronger than grade 8.  Oh, and I researched this after losing a bolt, substituting a mopar head bolt, and breaking it off in a freshly assembled engine.  The stock mopars and chevy bolts are about the same torque spec as grade 8, not so with AMC.  I used an aftermarket bolt for a small block chevy that was supposed to take "20 ft lbs more than stock" torque, about what the AMC bolts require.  Best bet is to find somebody that has a 290-343-390 head bolt.
BB


Posted By: bigbad69
Date Posted: Jul/11/2009 at 1:14pm
I tried the cheap and dirty approach when I broke the aforementioned head bolt and bought a grade 8 bolt as a replacement. It twisted apart long before I got to spec'd torque. That's when I said "f$%& it, just pay the man", and got the ARP bolts. So BB is correct, grade 8s won't work.

If this fellow is on a tight budget, a wanted add for a used head bolt here would likely work. I probably have what's left of the factory set from my engine build in the garage somewhere. I would guess there are more closer to him.

r08ert209cali, that was a kind offer, but 304 bolts will be 1/2". This fellow needs 7/16"


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69 Javelin SST BBO 390 T10


Posted By: farna
Date Posted: Jul/11/2009 at 2:45pm
I just checked a 73 TSM. V-8 head bolts at 110 ft/lbs, I-6 at 105 ft/lbs. These should all be 1/2" bolts.
69 TSM: V-8 head bolts at 90-100 ft/lbs, I-6 at 80-85 ft/lbs. V-8 had 7/16" bolts, I-6 1/2".

V8s went from 7/16" to 1/2" head bolts in 1970 with the taller deck block (GEN-2 = 7/16", GEN-3 = 1/2").

Out of curiosity, I checked a 61 TSM also. V-8 and I-6 head bolts, 60-65 ft/lbs. I don't recall whether the GEN-1 V-8 has 1/2" or 7/16" head bolts, but I believe they are 1/2" -- everything else was "over" built!

Interestingly, the I-6 went from 60-65 in 69 to 75-85 in 1970, 80-85 in 71-72, then to 105 in 73. As far as I recall the 232 family always had 1/2" head bolts until 1980 calendar year. Along with the aluminum intake, four counterweight crank, and other weight reduction features came 7/16" head bolts. Went back to 1/2" in late calendar year 1986 with the intro of the 4.0L -- 258 got 1/2" head bolts along with the 4.0L.

So the early V-8s can use grade-8 bolts, but the later ones (sixes and V-8s) need stronger one.
According to an engineer's handbook, a 1/2" grade 8 bolt has a max dry torque of 119 ft/lbs (7/16" only 78 ft/lbs!). So a properly manufactured one would be right near the threshold at 110 ft/lbs. SHOULD hold, but too close to the max for me too! I've used grade 8 bolts in 196s and early 232s, not in the V-8s. Doesn't sound like a good idea, except for the GEN-1. Definitely won't work with the GEN-2 7/16" bolts!!


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Frank Swygert


Posted By: mramc
Date Posted: Jul/11/2009 at 3:12pm
I'd check with one of the big 3 AMC parts vendors. I just checked APD Doug Noel site and for some reason he has 290 V-8 head bolts listed as a seperate different item. I know Doug use to have the bolts available individually, but now seem to only have new sets. But Doug Galvin could probably come up with a used head bolt or bolts for the guy for a low buck figure, if all he needs is one or two. LRDaum  

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LRDaum


Posted By: r08ert209cali
Date Posted: Jul/11/2009 at 4:18pm
Originally posted by bigbad69 bigbad69 wrote:

I tried the cheap and dirty approach when I broke the aforementioned head bolt and bought a grade 8 bolt as a replacement. It twisted apart long before I got to spec'd torque. That's when I said "f$%& it, just pay the man", and got the ARP bolts. So BB is correct, grade 8s won't work.

If this fellow is on a tight budget, a wanted add for a used head bolt here would likely work. I probably have what's left of the factory set from my engine build in the garage somewhere. I would guess there are more closer to him.

r08ert209cali, that was a kind offer, but 304 bolts will be 1/2". This fellow needs 7/16"


That sucks. I have a ton of them.


Posted By: Steve_P
Date Posted: Jul/11/2009 at 4:20pm
Originally posted by BassBoat BassBoat wrote:

The torque specs for a grade 8 bolt are less than the stock head bolts, so my interpretation is that the stock head bolts are stronger than grade 8.  Oh, and I researched this after losing a bolt, substituting a mopar head bolt, and breaking it off in a freshly assembled engine.  The stock mopars and chevy bolts are about the same torque spec as grade 8, not so with AMC.  I used an aftermarket bolt for a small block chevy that was supposed to take "20 ft lbs more than stock" torque, about what the AMC bolts require.  Best bet is to find somebody that has a 290-343-390 head bolt.
BB
 
The 7/16 AMC OE head bolts are grade 8.  The original torque spec, in 1967 was the typical grade 8 spec (72-77 lb-ft).  I remember this because I was a month old Big smile and changing a lot of AMC V8 head gaskets.  Ok, just kidding, there is a TSB on the bolt torque (april 5 1967). 
 
There were head gasket failures so they revised the head gasket and also raised the torque spec to 90-100 lb-ft to help deal with this.  This is the listed torque spec in the 68-9 TSM and, as said, is significantly greater than recommended for a 7/16 gr 8 bolt so it is not uncommon to have the OE 7/16 bolts break. 
 
So, with stock compression and stock head bolts I would use the industry recommended, lower, grade 8 torque as head gaskets now are much better than the originals in 67


Posted By: billd
Date Posted: Jul/11/2009 at 5:13pm
Steve I think you just hit it! He's got a 77 and he was going by 1977 torque specs..... if he took those old 7/16 to 110, that's the problem or at least a contribution.
Thank you much to ALL who responded.
And yes, thanks for the offer, but he needs PRE-1970 bolts for sure.


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Posted By: amx39068
Date Posted: Jul/11/2009 at 5:43pm
That is correct, the earlier head bolts have the lower torque specs and they will break when using too much torque...ask me how I know!
 
Any early AMC V-8 head bolt will work as will the later AMC V-8 head bolts if he were to drill and tap the block head bolt holes in the block from 7/16th threaded holes to 1/2 threaded holes.  I have two different 68/69 390s, one with stock 7/16ths head bolts installed and the other with the block head bolt holes enlarged to 1/2 size and using 1/2 head bolts.


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Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development



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