I learned me something today about torque-to-yield bolts.

[j-c-c-62]

A very thorough redundant review of TTY bolt concepts, that was pretty much however IMO covered in just 3? paragraphs already in this thread.
The main new takeaway here strangely, best outcome it seems, it reduces chances of overtightening, by widening the point between yield and failure, but by making the fastener a one and done solution.

 

[Triplegreen500]

I think the article touched on many things that this thread hadn't yet, such as load spreading, consistent loading, and superior, more consistent clamping forces. To me, the thread seemed more of a "wtf" session without any real information about what they do and why they're preferred in certain applications.

 

[j-c-c-62]

I think the article touched on many things that this thread hadn't yet, such as load spreading, consistent loading, and superior, more consistent clamping forces. To me, the thread seemed more of a "wtf" session without any real information about what they do and why they're preferred in certain applications.

Not sure "load spreading, consistent loading, and superior, more consistent clamping forces" are problems a competent mechanic suffers or needed to be covered for those who aren't, as they are the one's most likely to reuse a TTY bolt in the first place with or without this article..

 

[69Bee]

A lot of reasons and explanations of TTY fasteners has been covered here, but there are still a few misconceptions.

1) TTY bolts DO provide a more consistent "Clamp Load" for the fasteners over just a torque spec.
2) The Torque in the "Torque & Angle" procedure assures the MLS head gasket to compress and seat to provide a more complete and accurate tightening of the head.
3) TTY fasteners are usually necked down under the head.
4) Not all modern fasteners using a torque & angle are TTY but most of the important ones are (head, rod, main, balancer, camshaft, etc...)
5) In the "Angle" phase, the bolt will stretch to the "Clamp Load" portion of the curve, just before the "Elastic" phase starts.

A TTY fastener cannot be reused because the bolt is stretched past the "Memory" phase and does not return to its initial length. Therefore, when a bolt is reused, it will start from the elongated state and be tightened past the "Elastic" phase and will usually break before fully tightening. Most bolts will be identified in the manual as "Replace Only" while others (Cummins) will use a torque & angle for rods and mains for a more consistent tightening. I have seen a "Fastener Stretch" spec in manuals for non-TTY bolts as they can eventually stretch too far also. Has anyone ever broken a regular bolt while tightening before? It failed due to stretching. A head gasket can fail with both TTY and regular fasteners. If the engine is over heated, the fire ring will get crushed and when the engine cools down, it will create a weak spot that gets blown out on subsequent operations. A HP engine can mechanically blow out a gasket due to high cylinder pressure which is why performance fasteners are used to provide a higher clamp load on the gasket. Yes, it is a pain to replace TTY fasteners once they are tightened (even if you never start the engine), but that is a function of their design.

I know there is more I wanted to say, but my hand is hurting from typing and re-typing correcting spelling errors...

 

[j-c-c-62]

"2) The Torque in the "Torque & Angle" procedure assures the MLS head gasket to compress and seat to provide a more complete and accurate tightening of the head."

What I am failing to see here is that procedure does not require a TTY bolt. My feeling here is the TTY solution reduces somewhat overtightening issues, but unless breakage occurs with overtightened non TTY bolts and/or other adjacent bolts are also under tightened, I am not seeing the basis for concern here in automotive applications, except for use by low skilled assemblers.
Best as I can tell, they are never used in/on wheel studs, one of the most safety critical items on a car.
I'll review my Carroll Smith fastener bible and confirm proper tightening for nearly all bolts properly sized is above the 80%? range.
I am not seeing where the performance magic is in improving that consistency a few? percentage points.
Regardless, I admit real world measuring of fastener stretch of any kind is the holy grail of tightening a fastener, if possible

 

[RemCharger]

In a headbolt application it allows for expansion of the head. Then springs back down when contracted.

 

[Triplegreen500]

In a headbolt application it allows for expansion of the head. Then springs back down when contracted.

Exactly. Think "shock absorber" versus "solid metal rod".

It allows for heat expansion and contraction, without variance to the clamping force. It's not the torque spec that does it; it's the material characteristics.

 

[Cop car wagon]

MLS gaskets, especially on all aluminum engines, "float" between the head and deck. That is why they have specific profile smoothness spec. to deck finish. A rough finish will hold the gasket, and lead to early sealing failure.
All aluminum engines expand, and if held by a non giving stud combo, will compress the gasket and require constant retorquing. Until the gasket is so compressed it fails.
I run cheap tty's on my boosted all alloy motors. I do log the final torque pound spec. on my final 90° pull. They are usually within a .5 ft pound of each other.
Rods are usually within .2#
We have old mopars. So clean up some used bolts, oil the threads and torque away.

 

[padam]

Head bolts are one thing.
Cam bolts, crank bolts, flywheel and clutch. I will use a torque wrench for this kind of stuff that I consider critical.

But for most other things, especially on a daily driver, I don’t use a torque wrench.

Am I in the minority here?

 

[69Bee]

"2) The Torque in the "Torque & Angle" procedure assures the MLS head gasket to compress and seat to provide a more complete and accurate tightening of the head."

What I am failing to see here is that procedure does not require a TTY bolt. My feeling here is the TTY solution reduces somewhat overtightening issues, but unless breakage occurs with overtightened non TTY bolts and/or other adjacent bolts are also under tightened, I am not seeing the basis for concern here in automotive applications, except for use by low skilled assemblers.
Best as I can tell, they are never used in/on wheel studs, one of the most safety critical items on a car.
I'll review my Carroll Smith fastener bible and confirm proper tightening for nearly all bolts properly sized is above the 80%? range.
I am not seeing where the performance magic is in improving that consistency a few? percentage points.
Regardless, I admit real world measuring of fastener stretch of any kind is the holy grail of tightening a fastener, if possible

With all aluminum engines, bi-metal engines, open deck blocks, MLS gaskets, etc... a better method of tightening was dictated. I highly doubt the Automotive Engineers sat around a table devise a way to make a profit by using "one-use" fasteners. Can you change over to "multi-use" fasteners, sure, I do it all of the time. ARP head bolts/studs, ARP rod bolts, ARP main bolts are routinely used for that purpose. Yes, bolt stretch measurement is the best-case scenario, but the only bolt I know that can be done with is a connecting rod bolt with the proper gauge. While you might, how many people use a "Thread Chase" tap as opposed to a regular cutting tap to clean out the threads or do anything at all. Okay, hand hurts again. Typing after surgery sux!

 

[69Bee]

Head bolts are one thing.
Cam bolts, crank bolts, flywheel and clutch. I will use a torque wrench for this kind of stuff that I consider critical.

But for most other things, especially on a daily driver, I don’t use a torque wrench.

Am I in the minority here?

Yes, I use a torque wrench on EVERY bolt! If there isn't a listed torque spec, I refer to the grade, diameter, and thread pitch and torque accordingly.

 

[70bigblockdodge]

Torque to degree is not always torque to yield. Torque to yield is a one time use bolt. Torque to degree is more accurate than ft lb reading because it removes the high load friction variables, valuable in areas such as brake parts that need no lube and are usually rusty. Head bolts and main bolts are done more and more torque to degree with torque to yield bolts because at 100 ft lbs it is hard to make even/constant pulls up to the number, or did you yank it right up there till it clicked. If torque ft lbs is reduced to something like 40/50 that is easy to pull up on then add another 90° and it's torqued.
Cummins Diesel N series engines had like 450 ft lb torque on head bolts. Those where a MF to do even with a 5' cheater bar on you bad *** torque wrench. 3406 Cat engines had like 100 ft lbs and then a certain number of flats to turn (or degrees if you will) we would torque those with a impact and 6 different length lines on the socket.
So the guy is not really wrong, but every bolt with degree torque is not a TTY. TTY bolts are springy to hold under variable loads and temperatures and multi-layer steel head gaskets. Those bolts holding the caliper brackets on are not that, they are more a shear load than anything.

 

[Kern Dog]

Head bolts are one thing.
Cam bolts, crank bolts, flywheel and clutch. I will use a torque wrench for this kind of stuff that I consider critical.

But for most other things, especially on a daily driver, I don’t use a torque wrench.

Am I in the minority here?

I don't remember the last time I ever used a torque wrench on an intake, any exhaust manifold or header, never on a spark plug, no water pump or housing, no oil pan or valve cover bolts, no suspension bolts either.

 

[1967coronet]

Waiting for Bob to weigh in on this one.

 

[padam]

Waiting for Bob to weigh in on this one.
View attachment 1922562

ask about weather to replace the factory carburetor attachment bolts with some high speed ones. That’s like saying “Voldemort.”

 

[j-c-c-62]

I don't remember the last time I ever used a torque wrench on an intake, any exhaust manifold or header, never on a spark plug, no water pump or housing, no oil pan or valve cover bolts, no suspension bolts either.

At my dad's garage in the early sixties he had a Champion? sales rep show up and the big thing at that time was spark plugs not being properly tightened. I suppose his sales pitch often challenged the shop owner to take a torque test with a bank of spark plugs to a suggested value of what 40? ft/lbs. Not sure how accurate the test or the sales rep's torque wrench was, but my dad's plugs only varied 2lbs off the target.
Pretty much ended the conversation.
I suspect I inherited some of his skill set, I can eyeball 100' within 3', an inch with 48", level a 40' stage within 1", I don't need no stinking tape measures, laser levels, or torque wrenches, unless I need to prove something.
I do like spell check though.

 

[khryslerkid]

I don't remember the last time I ever used a torque wrench on an intake, any exhaust manifold or header, never on a spark plug, no water pump or housing, no oil pan or valve cover bolts, no suspension bolts either.

I used to be like that also but with age and RA it's hard for me to tell just how much I'm turning a bolt anymore. I have to have a torque spec on most things now days.