Why do head gaskets blow?
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Cargo Master
Joined: Oct 2005
Posts: 2,599
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From: Farmington NM
Why do head gaskets blow?
Why do head gaskets blow?
The 6.0 Power stroke Diesel had developed an unfair reputation for head gasket problems. This is misleading, the actual gaskets seldom fail, and the issue is with the torque to yield head bolts stretching. <O
When International designed the 6.0 a decision was made to use bolts instead of studs for service reasons. With studs the heads could not be removed from the motor with it in the truck. Removing the cab was not considered an option at that time because of the special procedures and extra equipment that would be required. Also with previous motors head bolts had not been a significant failure point. The decision to use torque to yield bolts was a cost and ease of production issue. Normal steel bolts have some elasticity in them, if the bolt is stressed it can return to its original length after the stress is removed. Torque to yield (TTY) bolts, are also commonly referred to as angle torque or stretch bolts. Compared to conventional type bolts, TTY bolts offer the engine manufacturer a number of advantages including greater flexibility of design, reductions in component costs, more accurate assembly and reliability of seal. Engines designed utilizing TTY head bolts require fewer head bolts to achieve the desired clamping loads then those using conventional bolts. With fewer bolts the engine manufacturer has more flexibility in cylinder head and block design as well as reducing the cost of the engine. Conventional head bolts simply just did not wear out. Torque to yield head bolts however, by the very nature of their design, do wear out and should NEVER be reused or subject to stress beyond their design. Unlike a conventional bolt, TTY bolts are tightened beyond their elastic range past their yield point from which the bolt material can recover to its original length, and into the plastic phase of the bolt material. The bolt is permanently stretched and for this reason should not be reused. The reliability of these bolts once stretched is greatly reduced. If the bolt is stretched it WILL NOT return to its original length or strength.
<OSo what causes them to stretch? Peak cylinder pressures beyond the design limits. This over pressure can be caused by many factors on both stock and modified engines
On stock engines injector issues that cause over fueling can cause this as well as turbo vanes sticking resulting in a severe over boost condition.
<OAftermarket tuners that are improperly designed are the biggest cause of this issue. There are 3 ways of increasing power on a diesel engine without hardware modifications. Increasing fueling, increasing timing advance, and increasing engine boost. In the early days if 6.0 tuning the preferred method of increasing power was to advance the timing of the fuel injection. This gave a great power increase with less smoke and peak EGT issues. Extra fuel will also increase the power with a disadvantage of excessive smoke and possible high EGT unless it is balanced with good airflow. Boost by its self will show only minor power increases unless more fuel is added.
<OWhen the timing is increased the combustion cycle shows a very sharp spike in cylinder pressure. This peak pressure can exceed the design limits of the head bolts and cause the heads to lift. During the time the heads are lifted combustion gasses will enter the cooling system causing it to overpressure and expel coolant out of the degas bottle. After the engine returns to normal pressures the heads will reseat, but the damage is done. The bolts are now weakened and will let the heads lift again at even lower pressures.
<OWith proper understanding of how these engines operate and extensive testing safe reliable power can be achieved with modern tuners. If you are looking for modest performance increases head studs are not required if you purchase from a reputable dealer.<O
The 6.0 Power stroke Diesel had developed an unfair reputation for head gasket problems. This is misleading, the actual gaskets seldom fail, and the issue is with the torque to yield head bolts stretching. <O
When International designed the 6.0 a decision was made to use bolts instead of studs for service reasons. With studs the heads could not be removed from the motor with it in the truck. Removing the cab was not considered an option at that time because of the special procedures and extra equipment that would be required. Also with previous motors head bolts had not been a significant failure point. The decision to use torque to yield bolts was a cost and ease of production issue. Normal steel bolts have some elasticity in them, if the bolt is stressed it can return to its original length after the stress is removed. Torque to yield (TTY) bolts, are also commonly referred to as angle torque or stretch bolts. Compared to conventional type bolts, TTY bolts offer the engine manufacturer a number of advantages including greater flexibility of design, reductions in component costs, more accurate assembly and reliability of seal. Engines designed utilizing TTY head bolts require fewer head bolts to achieve the desired clamping loads then those using conventional bolts. With fewer bolts the engine manufacturer has more flexibility in cylinder head and block design as well as reducing the cost of the engine. Conventional head bolts simply just did not wear out. Torque to yield head bolts however, by the very nature of their design, do wear out and should NEVER be reused or subject to stress beyond their design. Unlike a conventional bolt, TTY bolts are tightened beyond their elastic range past their yield point from which the bolt material can recover to its original length, and into the plastic phase of the bolt material. The bolt is permanently stretched and for this reason should not be reused. The reliability of these bolts once stretched is greatly reduced. If the bolt is stretched it WILL NOT return to its original length or strength.
<O
So what causes them to stretch? Peak cylinder pressures beyond the design limits. This over pressure can be caused by many factors on both stock and modified enginesOn stock engines injector issues that cause over fueling can cause this as well as turbo vanes sticking resulting in a severe over boost condition.
<O
Aftermarket tuners that are improperly designed are the biggest cause of this issue. There are 3 ways of increasing power on a diesel engine without hardware modifications. Increasing fueling, increasing timing advance, and increasing engine boost. In the early days if 6.0 tuning the preferred method of increasing power was to advance the timing of the fuel injection. This gave a great power increase with less smoke and peak EGT issues. Extra fuel will also increase the power with a disadvantage of excessive smoke and possible high EGT unless it is balanced with good airflow. Boost by its self will show only minor power increases unless more fuel is added. <O
When the timing is increased the combustion cycle shows a very sharp spike in cylinder pressure. This peak pressure can exceed the design limits of the head bolts and cause the heads to lift. During the time the heads are lifted combustion gasses will enter the cooling system causing it to overpressure and expel coolant out of the degas bottle. After the engine returns to normal pressures the heads will reseat, but the damage is done. The bolts are now weakened and will let the heads lift again at even lower pressures. <O
With proper understanding of how these engines operate and extensive testing safe reliable power can be achieved with modern tuners. If you are looking for modest performance increases head studs are not required if you purchase from a reputable dealer.<O
Post Fiend
Joined: Oct 2005
Posts: 10,626
Likes: 7
From: Plano TX and Brentwood TN
Originally Posted by KRDiesel
<O
With proper understanding of how these engines operate and extensive testing safe reliable power can be achieved with modern tuners. If you are looking for modest performance increases head studs are not required if you purchase from a reputable dealer.<O
Senior User
Joined: Jan 2006
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I had my heads done at 34K on my 06. My dealership told me that there was a "torquing" issue at the Factory during the builds. He said that the new headbolts and new torquing process would solve this forever. Has anybody had to do the head bolts a second time (with or without a tuner?). thanks rc
Post Fiend
Joined: Oct 2005
Posts: 10,626
Likes: 7
From: Plano TX and Brentwood TN
Originally Posted by rchouser
I had my heads done at 34K on my 06. My dealership told me that there was a "torquing" issue at the Factory during the builds. He said that the new headbolts and new torquing process would solve this forever. Has anybody had to do the head bolts a second time (with or without a tuner?). thanks rc
Elder User
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From: Ontario Canada
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Elder User
Joined: Sep 2007
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From: S CAL
I happen to agree with KRDiesel. I believe that the majority of blown head gaskets are due to tuners or from over boosting from a sticking turbo. I have caught my own truck boosting all the way up to 40 PSI when towing from a stuck turbo. On the 03 and 04 trucks that have no gauge for boost how many of them blew out their head gaskets not even knowing that the turbo was over boosting. I agree that the head bolt design could have been better but to say that the bolts are the problem for head gaskets failures I do not agree with.
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Thread Starter
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Cargo Master
Joined: Oct 2005
Posts: 2,599
Likes: 2
From: Farmington NM
Like all enginering disasters, It is never a single issue, it is a chain of issues!
Tuners that are inproperly programed or used, Sticking turbos, TTY bolts, these all are factors.
Tuners that are inproperly programed or used, Sticking turbos, TTY bolts, these all are factors.
Post Fiend
Joined: Oct 2005
Posts: 10,626
Likes: 7
From: Plano TX and Brentwood TN
The thing is that Ford has already done a modest HP boost compared to the International version of the same engine. Once they did that they pretty much forced the need for something more substantial then what International originally put on there. I'm not saying tuners can't be responsible on their own for head failure, but most people's evidence for that suggests a connection not definative proof that it did. I honestly do not believe that it's one thing that can cause it, it might be one thing that pushes it over the edge, but I honestly doubt that it's one thing that truly begins and ends with it with regard to the damage.
Postmaster
Joined: Apr 2004
Posts: 2,654
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From: Bossier City, LA
One thing that was left out of this thread, IH also had some machining tolerance issues. This has been discussed that with the inadaquate bolting system IH came up with, that actual heads were "warp induced" due to this design and torquing proceedures. Also several Ford dealerships received brand new heads that were out of flat according to the allowable tolerance. The issue could have been solved from the factory if hydraulic stretched studs would have been used. This would have pulled the entire head down, to torque in one shot.
Thread Starter
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Cargo Master
Joined: Oct 2005
Posts: 2,599
Likes: 2
From: Farmington NM
I am doing alot of research on the various problems with our heads. I have found out alot of interesting information over the past week that will be included in future tech tips.
Senior User
Joined: Jul 2006
Posts: 226
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From: Jeffersonville , Indiana
Originally Posted by mrxlh
One thing that was left out of this thread, IH also had some machining tolerance issues. This has been discussed that with the inadaquate bolting system IH came up with, that actual heads were "warp induced" due to this design and torquing proceedures. Also several Ford dealerships received brand new heads that were out of flat according to the allowable tolerance. The issue could have been solved from the factory if hydraulic stretched studs would have been used. This would have pulled the entire head down, to torque in one shot.
