I love my Fords, but we all know some of their "better ideas" have been less than great. I have yet to understand the thinking behind the use of torque to yield head bolts. In my mind, if you torque a bolt to it's yield point, then "any" additional load on it is going to cause the bolt to yield. Surely they calculated the pressures exerted, and allowed sufficient margin of error. I realize that if you tune the engine that you are changing those pressures, but even a stock engine is doomed to fail eventually.

 

Lot's of head bolt's in all brand's are tty. My cousin Just replaced the Head Gasket, in his John Deere Skid Steer, Diesel, and it utilized TTY bolt's.
The problem is International didn't use enough of them, and on earlier model years, didn't torque them correctly.
Stud's definately would have been better with the design, and lack of bolts.

 

IF and IF installed correctly under the recommended procedure, and used in the correct cylinder pressure as manufactured, Torque to Yield bolts work fine. History: Quality control at the engine assembly plant was lacking as robots did the procedure on the assembly line, some were found loose by servicing dealers you could remove by hand... thus creating the debate and other unmentionable which lead to Ford and IH separating ways. The Ford 6.0L Diesel is actually the IH VT365.

Add one tuner, 400+ HP and you can easily compromise the value leading to a failure... If I missed anything, let me know. Nice video...

 

Exactly TTY bolts are by far the most prevalent means of attaching cylinders in the diesel industry, from 30 hp generators to 500 hp CAT C15 OTR engines.

As mentioned, Navistar didn't design the application correctly, too small and too few. A good diesel will have at least 6 bolts surrounding each cylinder.

Josh

 

Built a lot of Cummins, Cat and Detroit classs 8 truck engines in our shop over the years and don't remember any TTY head bolts. There was a Torque angle which was to prevent a false reading on the torque due to friction.

 

Hmm...I thought that was the tell. If the torque procedure called for a torque angle measurement it was a TTY bolt. Is that incorrect?

 

I don't know about the newer models. Last ones we built before retirement were late 90's early 2000, but with torques up in the 175 to 220 range friction was a factor when pulling them down, using a torque angle reading meant you were getting an equal clamping force without regard to the effect of friction on the bolt head. While I guess you could call it yield in that the bolt would stretch a little, some mechanics actually reused the bolts if they were within tolerance. When I think of torque to yield, I think of a bolt that has reached it's maximum tensile strength and anything more will cause it to deform permanently.

 

You're right... Torque to a specified amount and then add the angle on the end. For example Torque to 35 then 65 then 85 ft.lbs then 90 degrees.

Almost all Deere engines use TTY bolts. The biggest difference for TTY is you must replace them when loosened.

The CAT C15 is most Definately a TTY head bolt btw.

 

My first experience with torque angle specs was on an early '80's Mercury Topaz. I asked some "old guys" about it (they knew everything) and was told it had to do with the expansion rate differences between the aluminum head, iron block, and steel bolts. The bolts just had a little stretch to them to compensate and would maintain tension better than a high tensile bolt. Tightening them with the torque angle method resulted in a more consistent "tightness" across all the bolts, which was more important than what the actual "tightness" was (within a reasonable window).

 

FYI, A lot of bridges and building structures are assembled with tty bolts. When done properly within design specs they are very reliable.

 

But chicks prefer studs. Maybe IH needs to hire more women.

 

All bolts are elastic. When you tighten a critical bolt to specs, you’re actually stretching the bolt. As you stretch the bolt, it wants to return to its original length. Based on the quality of steel used in the fastener, the diameter of the fastener and how far you stretch it, the load or force applied to the joint (the two pieces being fastened together) changes. Unfortunately, every fastener has an elastic limit, commonly referred to as its yield point, or more properly, "the threshold of yield." Up to this point, if the load on a fastener is released, the fastener will spring back to its original length. When a fastener is stretched into the yield zone, some of the elasticity is permanently lost, and the fastener will remain somewhat elongated when the load is removed. The further you stretch the fastener into the yield zone, the more elongation you get. A torque to yield bolt is at it's maximum load, anymore and it becomes elastic. Just because you pull a bolt to TTT or angle, does not mean you are bringing it to it's yield point.

It's my understanding the automotive industry came out with the Torque to Yield method of tightening in order to use a smaller bolt. The 3406 or C15 Cats that I ran prior to 2003 did not use the torque to yield method of tightening. Nor did the Cummins or Detroits. I believe Cummins may have switched to torque to yield on their rod bearings. Based on the load exerted on the head bolts of a class 8 engine, I don't see how a TTY would work.

I believe that a torque to yield method of tightening on a non turbo gas engine may work where you're looking at much lower loads, but obviously there are to many variables they overlooked when they tried it on the 6.0.

 

Caterpillar switched to TTY head bolts in 1993.

Josh