UNRULEE said:

I really don't see how a bolt that acts as a "spring" can can keep a head planted where it should be on a block in constant varying amounts of boost and cylinder pressure.

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All bolts act as a "spring" when properly tightend or they would not provide the clamping force necessary to keep the pieces clamped together. The bolt load applied to the bolts when they are torqued is specified by the design engineer so that the bolt exerts the proper clamping force to prevent cylinder lift off during normal operation of the engine.

Under the application of load, all bolts exhibit four main phases; elastic phase, yield point, plastic phase and shear point. In the elastic phase a bolt will stretch under tension but return to its original length when the load is removed. As we continue to increase the load the bolt reaches the yield point and enters the plastic phase from which it can no longer recover to its original length when the load is removed and is now permanently stretched. If we continue to increase the load beyond the bolts ultimate tensile strength the shear point is reached and the bolt material wastes & breaks.

A conventional head bolt is generally tightened to within 75-80% of its yield point. Friction on bolts results in resistance to turn. 90% of the load used to turn the bolt is required to overcome friction the remaining 10% is used to stretch the bolt to 80% of its yield point. Unfortunately do to the inaccurate nature of Torque-to-turn tightening methods the head bolts will vary in clamping load up to about 35% from bolt to bolt. This results in uneven loading on the head gaskets, can lead to bore distortion resulting in excessive blow by and gasket failure. In order to build a more reliable engine the load variance from bolt to bolt must be minimized, but unfortunately with conventional resistance-to-turn tightening methods of conventional bolts it is difficult to reduce this below 35%.

In order to reduce the bolt-to-bolt clamping load variance engine builders started using Torque-to-Angle and bolt stretch gauges to achieve proper bolt loading. Stretch gauges are more accurate than the Torque-to-angle method but can only be used were both ends of the bolt can be measured simultaneously (ie. Rod bolts). Since stretch gauges cannot be used on head bolts the Torque-to-angle method became the preferred method to properly load blind bolts. In addition to the Torque-to-Angle method, the use of studs also allows for a more uniform bolt-to-bolt clamping load. This is do to the fact that studs are only loaded in the vertical axis when tightened unlike bolts which are load in both the twisting axis & vertical axis simultaneously. By using Torque-to-angle or head studs the bolt-to-bolt clamping load variance can be reduced to about 15%.

Heads studs have the advantage of being more accurately loaded, make installing heads and gaskets faster on a race engine. Head studs however can be impractical on a daily driver do to the inability to remove the heads with the engine installed in the car on many models.

Torque-to-Yield bolts are loaded beyond the yield point when properly tightened. TTY bolts are used were consistent exact clamping loads are required to be maintained. This is especially needed on parts that have high thermal expansion & contraction characteristics (aluminum fits this category, aluminum has about twice the expansion rate of steel). By stretching the TTY bolts beyond the yield point into the plastic phase, gives them the resilience needed to maintain the proper clamping force on the heads & gaskets over thousands of heating & cooling events during the engines use without exceeding the clamping force that would permanently deform the head gaskets, cause brinelling of the head surface at the fire rings and distort the aluminum around the head bolts. Torque-to-Yield bolts achieve a more consistent even clamping load across the head-to-block mating surface resulting in a bolt-to-bolt clamping load variance of about 7%.

Compared to conventional bolts, TTY bolts offer the engine designer a number of advantages. Engines designed using TTY head bolts require fewer head bolts to achieve the desired clamping loads than those using conventional bolts, fewer bolts allow the engine designer more flexibility in cylinder head and block design, more accurate head block clamping pressure, less deformation of cylinder shape and a more reliable head gasket seal.

Standard bolts & studs are loaded within their “elastic range” and TTY bolts are loaded into their “plastic range”. It is true that the bolts/studs loaded within there elastic range will be able to withstand a wider range of head lift off pressure variance than TTY bolts loaded into their plastic range, before experiencing permanent bolt failure and loss of clamping pressure. However, standard bolts/studs tightened within their elastic range will perform poorly on engines that have components made of high thermal expansive materials (ie aluminum) and/or use MLS head gaskets.

On engines that contain high thermal expansive metals and/or MLS head gaskets TTY bolts are needed to prevent premature head gasket failure. When standard bolts/studs are used on engines containing high thermal expansive materials the standard bolts/studs are loaded to a higher clamping force as the metals expand resulting in a head-to-block clamping load that is to high resulting in permanent over compression of the head gaskets, distortion of the bolt holes, distortion of the cylinder bores, brinelling of the head/block surface and fire ring failure of MLS gaskets.

Now with the 6.0 the head bolts pass through the aluminum rocker box and MLS gaskets are used. The aluminum rocker box thermally expands and contracts at a very high rate which would cause standard bolts/studs to increase there clamping pressure beyond the elastic compressive range of the MLS head gaskets. The increased clamping load on the head/block junction do to the use of standard bolts/studs results in MLS gasket failure, distortion of the cylinder bores, brinelling of the mating surfaces.

It is true that TTY bolts are much closer to their shear point than standard bolts/studs and therefore TTY bolts will not sustain increased head lift off pressures that are beyond the engines normal design parameters like standard bolts/studs would before bolt failure.
Do to the 6.0 having its power outputs increased by FMC the engine is operating at very close to its peak design limits when it left the factory. If the engine is subjected to excessive boost levels, high internal temperatures or a combination of these the head gaskets and/or bolts will fail.

The 6.0 main head gasket failure points are high boost do to VRT turbo malfunctions or excessive internal temperatures do to oil cooler failure resulting in egr cooler failure. The high boost increases the head lift off pressure causing the TTY bolts to stretch closer to their shear point resulting in lost clamping force and the high internal temperatures cause the aluminum rocker box to expand beyond the normal design limits again over stretching the TTY bolts resulting in failure.

If you have a head gasket failure in a 6.0 you need to determine if it was caused by over boost or high internal temperature, repair this problem then install new head gaskets & TTY bolts.

mrxlh said:

Lee, there is a fix for this and it does include studs, however, there is not enough money in this specific issue to completely solve the problem on 6.0 heads. The inhearent problem has been solved by a ton of people way smarter than me about 30 years ago, however, again there is not enough call for it. It would include a head gasket re-design, a flat steel fire ring and a spacer plate for coolant passages with o-rings. In order for this to all "work" correctly the head would have to be torqued in 1 shot, meaning all the studs would be streched using hydraulic rams and then snugging the nuts. The releasing the pressure all at once and re-sstreching and checking the snuggness again.

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Well not exactly. The problem with studs is that you have aluminum rocker boxes which result in high thermal expansion thus leading to a head to cylinder clamping load that is to high when standard studs or bolts are used.
Fire rings work well on a high performance race engine or and engine that is run at a constant speed because the thermal cycling is minimal. However having an engine fire ringed that is placed in a daily driver will many times result in a premature failure of the fire ring do the the constant thermal cycling of a daily driver.
A much better solution for a daily driver is to have the heads o-ringed and use standared gaskets resulting in a much more consistant sealing of the cylinders and high reliability in an engine that sees constant thermal cycling.

As far as torquing all the bolts/studs at one time, this is actually done by the manufacture when they torque the TTY bolts in the 6.0 & 6.4 Powerstroke.

blackhat620 said:

this is actually done by the manufacture when they torque the TTY bolts in the 6.0 & 6.4 Powerstroke.

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But it's a known fact that many early 6.0's weren't torqued correctly from the factory, and that contributed to gasket failures.

UNRULEE said:

But it's a known fact that many early 6.0's weren't torqued correctly from the factory, and that contributed to gasket failures.

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A little known fact was that I didn't get my first headgasket job until 05. The 03s just got a lot of publicity (kind of like a plane crash, sensational, but doesn't actually happen that frequently). The early 6.0s also suffered from inadequate training. "White smoke out of the tailpipe, must be headgaskets!).

Wether it was 6.0 teething problems or inadequate training, the 03 and 04's seem to be the most troublesome.

A co-worker of mine has an 03 6.0 and he's had (and still has) issues.......he's replaced all of the injectors, and has had numerous other problems.

I'll knock on wood and say that my '05 has been pretty reliable. I did research and found a one owner truck that had zero engine warranty issues.

I'm not knocking the 6.0 here, I love my '05, just looking for a different perspective on them.

Zero problems with my 05 with 60k on the clock..well, a bad FICM, but pretty minor in the whole scheme of things.

I had a bad FICM as well, plus an egr valve and cooler.