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#1
10-29-2019, 10:25 PM
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Factory 4-bolt Main Cap Hardware Study
With a miserably cold day here in Colorado, I decided to start cleaning up the main caps and hardware inside. While doing so, I made an interesting (to me anyways) discovery that surprised me a bit. I noticed the 4" long 1/2-13 bolts tapered down very quickly off the head. What little shoulder present below the head would be occupied by the washer and therefore the factory bolt is very sloppy in the cap with a (required) washer. For comparison, I picked up a Grade 8 bolt at the local Ace Hardware. As the pictures show, the gold Ace bolt measures in at .46 compared to the factory .42 and it rests much tighter in the cap. What's even more interesting is that the shorter outside bolt has atleast 5x the shoulder length than the much longer and more essential inner bolt.
Is there a rationale for that which I can't think of? Seems to me that the gold bolt is the stronger of the two by design let alone age and usage.
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 Johnny US Army Retired1978 T/A 463 Pontiac, KRE 74cc 292CFM D-ports, Lunati VooDoo, V-max lifters, TKII, ATM 850 E85 carb, TCI TH-350 race tranny, 3600 converter 3.73 12 bolt 11.63@116.68mph 1981 T/A 4-speed 406 Pontiac, Merrick ported 6X heads, Comp 270S cam, Crosswind intake 750 Street Demon, 3.42 30 spline Eaton posi street car. 1980 Formula 350 Pontiac back burner project 1972 LeMans 350 Pontiac |
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#2
10-29-2019, 10:28 PM
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There made like that to give the proper yield at the factory TQ spec.Head bolts the same way if factory.Tom
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#3
10-30-2019, 12:39 AM
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What Tom said.
Also- The bolts are not intended to do any "locating" of the cap, just provide clamping force. When I use main studs I enlarge the cap holes to about 1/32" over the stud diameters. I do this any place a bolt or stud clamps a part that's located by other means- dowels, etc.
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Anybody else on this planet campaign a M/T hemi Pontiac for eleven seasons? ... or has built a record breaking DOHC hemi four cylinder Pontiac? ... or has driven a couple laps of Nuerburgring with Tri-Power Pontiac power?(back in 1967) |
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#4
10-30-2019, 05:58 AM
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X3 with the above 2!
Weather wise you may be cold, but I heard this morning that there's some place in Utah thats at - Fing 39 degree's!
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#5
10-30-2019, 06:33 AM
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Aren't the factory bolts grade 11 or something like that?
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My Half AN Injun..... |
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#6
10-30-2019, 09:18 AM
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I believe that bolt stretch is done at the thinnest portion of the bolt. Bolt stretch is what provides the clamping force (aka bolt torque). If a bolt does not have a thinner portion under the head then the stretch happens at the threads which greatly reduces a bolt's clamping force and leads to early failure.
__________________
Bill Strobel Owner Independent Towing 1965 GTO Nightwatch Blue/Aqua 2005 GTO Quick Silver/Red Fayetteville, NC Do It Right or Don't Do It All |
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#7
10-30-2019, 09:24 AM
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Quote:
GTO George |
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#8
10-30-2019, 10:43 AM
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Main Bolt Material .. Isnt it 300M ?
__________________
A man who falls for everything stands for nothing. |
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#9
10-30-2019, 11:07 AM
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Thank you Gentlemen for your replies and explanation. I was thinking the hardware store bolts would be stronger, I'm glad I asked.
__________________
Johnny US Army Retired1978 T/A 463 Pontiac, KRE 74cc 292CFM D-ports, Lunati VooDoo, V-max lifters, TKII, ATM 850 E85 carb, TCI TH-350 race tranny, 3600 converter 3.73 12 bolt 11.63@116.68mph 1981 T/A 4-speed 406 Pontiac, Merrick ported 6X heads, Comp 270S cam, Crosswind intake 750 Street Demon, 3.42 30 spline Eaton posi street car. 1980 Formula 350 Pontiac back burner project 1972 LeMans 350 Pontiac |
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#10
10-30-2019, 11:52 AM
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They might be too strong to get the proper yield at the factory specs!Tom
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#11
10-30-2019, 12:17 PM
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Yes, 300M material.
A bolt needs to stretch the proper amount to deal with the loads place on it , and as posted it needs to allow that stretch to take place in the proper area to not fail.
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#12
10-30-2019, 02:08 PM
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Nunzi warned me about some ARP head fasteners years ago with the TQ specs they gave.He was worried about them lifting and distorting the deck of our 50-60 year old blocks.ARP made me studs with back cut shanks to yield at 100lb with oil.After the first set they charged stupid money to do them.I saved the two Xtra originals they did for me and just have my machine shop back cut them for me.FWIW,Tom
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#13
10-30-2019, 03:05 PM
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Until my little project, I assumed new bolts were not available because they were hardware bolts. Since that is NOT the case, I really wonder why new bolts are not available? Of course studs are always an option but on a mild rebuild new bolts would be a nice option for peace of mind...
__________________
Johnny US Army Retired1978 T/A 463 Pontiac, KRE 74cc 292CFM D-ports, Lunati VooDoo, V-max lifters, TKII, ATM 850 E85 carb, TCI TH-350 race tranny, 3600 converter 3.73 12 bolt 11.63@116.68mph 1981 T/A 4-speed 406 Pontiac, Merrick ported 6X heads, Comp 270S cam, Crosswind intake 750 Street Demon, 3.42 30 spline Eaton posi street car. 1980 Formula 350 Pontiac back burner project 1972 LeMans 350 Pontiac |
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#14
10-30-2019, 03:07 PM
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You will run into the same deal with studs I think.tom
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#15
10-30-2019, 08:03 PM
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The Main Cap wave for-aft.
Thick shank bolts transfer the Wave into the block to promote cracks in the Web Thread hole |
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#16
10-30-2019, 08:39 PM
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Quote:
__________________
1967 Firechicken, 499", Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3550#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule. |
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#17
10-31-2019, 01:31 AM
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Quote:
__________________
Anybody else on this planet campaign a M/T hemi Pontiac for eleven seasons? ... or has built a record breaking DOHC hemi four cylinder Pontiac? ... or has driven a couple laps of Nuerburgring with Tri-Power Pontiac power?(back in 1967) |
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#18
10-31-2019, 01:56 AM
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I have had a couple CAT bolts on my HO heads for years mixed with factory.
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#19
10-31-2019, 02:50 AM
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Another factor in the reduced stock bolt diameter is that a stock bolt won't hit the sides of the bolt holes in the main caps. When standard sized studs are installed it almost always requires reaming the main cap holes so the stud doesn't rub and force the cap out of alignment, and even then it's a good idea to do a line hone to insure the caps have located properly.
__________________
Mick Batson 1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress. |
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#20
10-31-2019, 08:20 AM
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Good information to follow in posts, 3,6,11,17,19 . BTW, hardware store bolts if used in critical clamping applications, at the very least try to verify the bolt manufacturer. Lots of them are Chinese sourced grade 8 fasteners. They are NOT to be trusted as real grade 8. They could be anything from non-graded to grade 5. Chinese put a grade 8 head marking on them and out the door they go. I have had 2 situations now where fairly large "grade 8 fasteners" failed in a shear situation. One was on the caster wheels of an engine hoist. "grade 8", Ha. Rolled the hoist over an expansion joint in the concrete floor and the bolts sheared off like they were made of plastic.
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