Reusing TTY head bolts
- Thread starter pottymouth
- Start date
- Status
TTY bolts neck down and stretch at their designated waist, not the threads.
By the time the threads are involved, they are toast.
By the time the threads are involved, they are toast.
Originally Posted By: mechtech2
TTY bolts neck down and stretch at their designated waist, not the threads.
Well, not exactly. The "waist" is not a designated zone of stretch. When TTY bolts were first used, they used to have full diameter shanks, but later designs sometimes had either reduced diameter shanks. And, sometimes the shanks were reduced enough to be considered proper "waisted shank bolts" (shank diameter is less than the root (minor) diameter).
However, the purpose of these wasn't to have a designated zone for failure. Rather, the purpose was to reduce the risk of failure at the threads (where the root diameter is the smallest) by distributing stretch over the ENTIRE length of the threaded connector (i.e., bolt).
On a reduced diameter shank, within the working length of the bolt, the greatest tensile force is between the base of the head and the first engaged thread, and failure can occur at any point between, though usually in the middle. However, materials don't behave exacting to theory, so failure will occur along a bell curve, the middle being the most frequent.
Here's a Mercedes OM617 engine head bolt tightening procedure for two types of TTT/TTA bolts (full shank and reduced diameter shank). You can see that not all bolts have reduced diameter shanks:
Here's an 2000 LS1 head bolt that fractured at the thread (reduced diameter shank):
Source: 2000 LS1 Head Bolt Fractured at Thread http://www.ls1tech.com/forums/generation...pped-block.html
Here's a Dodge head bolt necking at the thread (waisted shank):
Source: Dodge Head Bolt Necking at Thread http://www.turbododge.com/forums/f4/f15/253467-do-i-need-put-oil-head-2.html
Here's the Chrysler TTA bolt necking check suggestion (posted earlier by Shannow):
Originally Posted By: mechtech2
By the time the threads are involved, they are toast.
By the time ANY portion of a bolt is necked down, it's toast, TTY, TTT, or any steel member used in any structural application, including bolts, rods, beams, trusses, etc....
My point was that, necking is easy to tell between threads, but it's difficult to tell at the top most thread where it meets the shank. Of course, necking at the shank would be obvious.
Btw, on my earlier post I recommended
Here's what I'd suggest (and feel free to comment):
1. Never re-use TTY bolts.
2. Re-use TTT/TTA bolts IF they are within manufacturer's specified stretch limits AND there is no neck down.
3. If manufacturer does not provide stretch limit, assume
3. Neck down at threads can be checked by threading a nut.
4. Neck down at shank can be checked by a straight edge.
5. Neck down at top-most thread cannot be checked easily, so to be on the safe side, re-use TTT/TTA bolts ONLY once.
TTY bolts neck down and stretch at their designated waist, not the threads.
Well, not exactly. The "waist" is not a designated zone of stretch. When TTY bolts were first used, they used to have full diameter shanks, but later designs sometimes had either reduced diameter shanks. And, sometimes the shanks were reduced enough to be considered proper "waisted shank bolts" (shank diameter is less than the root (minor) diameter).
However, the purpose of these wasn't to have a designated zone for failure. Rather, the purpose was to reduce the risk of failure at the threads (where the root diameter is the smallest) by distributing stretch over the ENTIRE length of the threaded connector (i.e., bolt).
On a reduced diameter shank, within the working length of the bolt, the greatest tensile force is between the base of the head and the first engaged thread, and failure can occur at any point between, though usually in the middle. However, materials don't behave exacting to theory, so failure will occur along a bell curve, the middle being the most frequent.
Here's a Mercedes OM617 engine head bolt tightening procedure for two types of TTT/TTA bolts (full shank and reduced diameter shank). You can see that not all bolts have reduced diameter shanks:
Here's an 2000 LS1 head bolt that fractured at the thread (reduced diameter shank):
Source: 2000 LS1 Head Bolt Fractured at Thread http://www.ls1tech.com/forums/generation...pped-block.html
Here's a Dodge head bolt necking at the thread (waisted shank):
Source: Dodge Head Bolt Necking at Thread http://www.turbododge.com/forums/f4/f15/253467-do-i-need-put-oil-head-2.html
Here's the Chrysler TTA bolt necking check suggestion (posted earlier by Shannow):
Originally Posted By: mechtech2
By the time the threads are involved, they are toast.
By the time ANY portion of a bolt is necked down, it's toast, TTY, TTT, or any steel member used in any structural application, including bolts, rods, beams, trusses, etc....
My point was that, necking is easy to tell between threads, but it's difficult to tell at the top most thread where it meets the shank. Of course, necking at the shank would be obvious.
Btw, on my earlier post I recommended
Here's what I'd suggest (and feel free to comment):
1. Never re-use TTY bolts.
2. Re-use TTT/TTA bolts IF they are within manufacturer's specified stretch limits AND there is no neck down.
3. If manufacturer does not provide stretch limit, assume
3. Neck down at threads can be checked by threading a nut.
4. Neck down at shank can be checked by a straight edge.
5. Neck down at top-most thread cannot be checked easily, so to be on the safe side, re-use TTT/TTA bolts ONLY once.
- Status
