Head Studs
Fleet Mechanic
Joined: Aug 2012
Posts: 1,760
Likes: 21
I believe I read somewhere that all OEM head bolts are TTY (Torque To Yield). This includes 7.3l as well as Cummins and Duramax. The TTY bolts stretch just a little, which is why they can't be re-used.
The studs don't stretch.
.
The studs don't stretch.
.
Post Fiend
Joined: Sep 2003
Posts: 6,096
Likes: 27
From: Mesa AZ
Studs stretch also.
Post Fiend
Joined: Sep 2003
Posts: 6,096
Likes: 27
From: Mesa AZ
A stud can be tightened into place with little to none twisting force. This means the fastener is only subjected to axial force, which results in a higher rating capacity.
The Oldsmobile Quad 4 engine had common studs that secured both the cylinder heads and the main bearing caps. During assembly they were torqued to stretch vs torque to yield. Those engines were virtually bullet-proof when pumping out power at extreme levels.
Torque to stretch is a far more accurate method. Back in my racing days, I used to purchase Mopar ARP connecting rod bolts for my cast iron Pontiac engines. I torqued them to stretch and routinely had engines making power will into the 6,000 rpm range (which isn't very common for the Pontiac design...)
Posting Guru
Joined: May 2006
Posts: 1,427
Likes: 1
From: Bryson City NC
A bolt gets rotated in its shaft in order to thread into place. This creates both twisting and axial forces on the bolt. When placed under load (in this case when cylinder pressures are most extreme, the heads want to separate from the block) the bolt has to deal with two different forces at the same time. As a result it's strength capacity is reduced a bit.
A stud can be tightened into place with little to none twisting force. This means the fastener is only subjected to axial force, which results in a higher rating capacity.
The Oldsmobile Quad 4 engine had common studs that secured both the cylinder heads and the main bearing caps. During assembly they were torqued to stretch vs torque to yield. Those engines were virtually bullet-proof when pumping out power at extreme levels.
Torque to stretch is a far more accurate method. Back in my racing days, I used to purchase Mopar ARP connecting rod bolts for my cast iron Pontiac engines. I torqued them to stretch and routinely had engines making power will into the 6,000 rpm range (which isn't very common for the Pontiac design...)
A stud can be tightened into place with little to none twisting force. This means the fastener is only subjected to axial force, which results in a higher rating capacity.
The Oldsmobile Quad 4 engine had common studs that secured both the cylinder heads and the main bearing caps. During assembly they were torqued to stretch vs torque to yield. Those engines were virtually bullet-proof when pumping out power at extreme levels.
Torque to stretch is a far more accurate method. Back in my racing days, I used to purchase Mopar ARP connecting rod bolts for my cast iron Pontiac engines. I torqued them to stretch and routinely had engines making power will into the 6,000 rpm range (which isn't very common for the Pontiac design...)
Excellent explanation ! I think I have it figured out now!
Smokie
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FordManiac1242
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Sep 26, 2012 12:34 PM
