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V8 head bolt question

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bigbad69 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2009 at 2:14pm
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"


Edited by bigbad69 - Jul/11/2009 at 2:17pm

69 BBO Javelin 390 T10
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2009 at 3:45pm
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!!
Frank Swygert

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mramc Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2009 at 4:12pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote r08ert209cali Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2009 at 5:18pm
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_P Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2009 at 5:20pm
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2009 at 6:13pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2009 at 6:43pm
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.
Dan Curtis, AZ AMC Collector Quality Restorations & Parts - amcmusclecars.com
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