| [GMCnet] Broken Exhaust Manifold Bolts [message #122697] |
Thu, 21 April 2011 21:57  |
Gary Bovee
Messages: 177
Registered: August 2008
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I just found two (2) broken exhaust manifold bolts tonight. I lucked out
and was able to get both of them out without to much trouble. They were
grade 5 bolts. Seems I remember some discussion about using grade 5 bolts
because they would not become brittle as easily as the grade 8 bolts because
of the heat exposure and then break. Did I dream this up or is this fact.
So my obvious questions is which grade bolts do you recommend I use - grade
5 or grade 8.
The Western States Rally is fast approaching and I have got to get this
thing back together and soon on the road.
Gary Bovee
Red Bluff, CA
78 Royale by Coachman
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| Re: [GMCnet] Broken Exhaust Manifold Bolts [message #122720 is a reply to message #122697] |
Fri, 22 April 2011 08:31  |
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Hardie Johnson
Messages: 483
Registered: January 2004
Location: Raleigh NC
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| Gary Bovee wrote on Thu, 21 April 2011 22:57 |
I just found two (2) broken exhaust manifold bolts tonight. I lucked out nd was able to get both of them out without to much trouble. They were grade 5 bolts. Seems I remember some discussion about using grade 5 bolts because they would not become brittle as easily as the grade 8 bolts because of the heat exposure and then break. Did I dream this up or is this fact.<>
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While it is true that grade8 bolts are less elastic than grade 5, ie., the difference between yield and tensile strength is a smaller percentage (130/150) 86% than it is for grade5 (92/120) 90%, that is minimal.
The proof load on grade 8 is 140% greater than grade 5.
The load on the exhaust flange is simple tension, and there is no impact involved, so grade 8 would be a good choice here. Grade 8 bolts are tempered at 800*F, how hot does the manifold get?
Here is an article that debunks the myth of brittle bolts:
http://www.rockcrawler.com/techreports/fasteners/index.asp
BTW, grade 8.2 bolts (as seen on eBay) are junk. Do not use them.
Hardie Johnson "Crashj"
1973 26 foot Glacier, White Thing
Raleigh NC
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| Re: [GMCnet] Broken Exhaust Manifold Bolts [message #122835 is a reply to message #122752] |
Fri, 22 April 2011 21:51 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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G'day,
And for those of you who don't own a set of Cobalt drill bits here's where
you can get sets CHEAP!
Harbor Freight SKU 36891 @ $49.99
Or:
Harbor Freight SKY 47653 @ $129.99 (currently on sale for $99.99)
I carry the SKU 36891 set in Double Trouble and have the SKY 47653 set in my
workshop in Sydney.
I find them to be good quality but you have to be careful because their
hardness makes them brittle and they can be broken easier than high speed
steel.
Regards,
Rob M.
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Hardie Johnson
Sent: Friday, April 22, 2011 11:21 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Broken Exhaust Manifold Bolts
Harry wrote on Fri, 22 April 2011 12:06
> Are Grade 8 bolts harder to drill out then Grade 5?
According to specs, grade 8 = Rc32-39, grade 5 = Rc25-34, cobalt steel drill
bits are Rc60-70, so it should not be an issue.
YMMV ;)
Proper application of Kroil* beforehand may avoid the issue.
"*Kano labs, or home made substitute"
--
Hardie Johnson "Crashj"
1973 26 foot Glacier, White Thing
Raleigh NC
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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