Yes, Kill Devil Diesel designed and sells aluminum heads for our 6.0 and some of their trucks are pushing 1800-1900 horsepower with double o-ringed heads and block. A few forum members have single o-ringed aluminum heads from KDD.

 

Jack,

Great info, interested to see where you end up with this.

How would you address the common conception that studs hold up to more horsepower than TTY bolts? A lot of people claiming to never have issues again after studs. Just curious, not trying to start an argument.

 

My other truck has TTY bolts. They were put in at 140K miles and the truck now has
220K miles on it and does not loose any coolant or make any excessive pressure.

I am tempted to go back to the TTY bolts and use a Felpro gasket set.

 

The studs vs TTY tightening is only for relatively stock motors. When you increase the combustion pressures you need a higher clamping force. To do that you need either stronger bolts or larger diameter bolts. The specialty ARP studs from the data are very strong bolts, but they are not tighten stressed in the same way that the OE TTY bolts are, which is why we can reuse them.

Based on ARP's own data of yield and clamping force at 210ft-lb they are stating we should use, that would be the normal bolt tightening point of 60-70% ( 71% to be exact) of yield based on the grade of the bolt. You can tension the bolts much higher, they have the yield strength for that. Which makes the use of their stronger then A2000 bolts just crazy unless you are putting out mass dyno power. We are not using the capability of the A2000 studs as we could be. But as we approach closer to the yield, the reusing ability is diminished even if we don't exceed yield. Most metallurgists will say you should only re-torque normally tensioned bolts about 5 times being conservative, 8 average.

Again, the point about the ARP studs is we are generating the same clamping force that it looks like we do when doing the TTY of the OE bolts. The only thing we are gaining is the ability to reuse the studs. Studs $450 vs the market for unused Powerstroke 6.0 TTY bolts on eBay for $17 shipped. ANWB says no one wants the bolts so they pull them out of gasket packages and toss the bolts.

A graph just looking at the stress-strain relationship, my red circle where TTY resides. Again, the ARPs spec is at "CLAMP LOAD".





At the bottom of the image where I looked at the gasket clamping pressures, I have a table looking at the clamp load we need. Again, where the bolts are is not where the gaskets are typically blowing, the bolts are not stretching unless we lose mass coolant and overheat the heads.

I was looking for specific data about the combustion pressures of the 6.0L, but could not find it. So I found an early SAE paper and I found a discussion in an engineering forum. I looked at past discussions of these two people and they appear to be in the industry.






The updated version of my table is this. We are not in the range of the big litre engines, and I have no way of knowing what the pressures are for some of the programming or the powerful dyno rigs. But calculating the peak combustion pressures is not that hard. I also found data I think from Mahle maybe when I was talking to FelPro that the design criteria is 3X peak. Knowing the clamping load stated by ARPs, and with the 10.9 bolts TTY are in the relative, and possibly higher range, I think the values are relevant. One cylinder, 4 bolts.




Aluminum heads bring in another factor due to their higher thermal expansion rate, and aluminum heads are the reason TTY tightening was put into practice by an article by Larry Carley, also I would argue some of what he wrote in other parts of the articleis not correct. Larry Carly

Why intentionally stretch the head bolts? Engineers discovered they can get much more even clamping on the head gasket if all the bolts are evenly loaded. Since variations in friction between bolts always cause some uneven loading, stretching the bolts guarantees all the bolts will exert the same clamping force regardless of the torque reading on the wrench. The result is improved cylinder sealing, longer head gasket durability and less cylinder bore distortion (for reduced blow-by and more power).



TTY head bolts are typically used on engines with aluminum cylinder heads (where there is a lot of thermal expansion) and with multi-layer steel (MLS) head gaskets. MLS head gaskets are very stiff gaskets with much less compressibility than standard soft-faced composition head gaskets. On the other hand, MLS head gaskets are almost bullet-proof and produce much less bore distortion than other types of head gaskets because they require less clamping force. But to seal properly, MLS head gaskets require very smooth (almost polished), flat surfaces on the head and block. This, in turn, requires very precise and even clamping loads by the head bolts. That's why TTY head bolts are used in these engines.

Comments from Bill McKnight, Director of Training for MAHLE Clevite during the same time frame, which shows the discrepancy in the relation of the gasket type.Torque-to-yield

In the mid-1980s, we started to see a move in engine fasteners to a new process called torque-to-yield (TTY). Head bolts were the first fasteners affected, although the technology has trickled down to other critical fasteners. The theory holds that the farther we stretch a fastener toward the threshold of yield, the more load it exerts on the joint.

Now you might say, ”If we want more load, we can always use a bigger diameter fastener.” That’s correct. Let’s use our (hypothetical) gasket example from Victor Reinz. We need 11,900 lbs. of load on each bolt. We can get that load by stretching a 7/16″ diameter bolt to the threshold of yield or by putting a very moderate load (requiring very little stretch) on a 9/16″ diameter bolt. The concern is on a head bolt application is that you get lots of change in the joint. Both gasket relaxations on a new installation, as well as thermal expansion on bi-metal designs, will cause changes to the joint dimension once the installation is complete. Head gasket relaxation causes loss of load from the fastener. The less stretch you have on the fastener, the more the loss of load. Let’s work our theoretical example:

7/16″ fastener stretched .070″ equals 11,900 lbs. of load;

9/16″ fastener stretched .030″ equals 11,900 lbs. of load;

A composition gasket installed at .045″ relaxes 25%, for a net loss of .011”.

7/16″ fastener loses 1/7 of the load, leaving 10,200 lbs.; and

9/16″ fastener loses 1/3 of the load, leaving 7,933 lbs.

As you can see, we’ve got a major sealing issue with the 9/16″fastener. Obviously, it’s a big advantage to keep the fastener diameter small and use maximum stretch to seal engines. Also, keep in mind that the longer in length the fastener is, the more it stretches to get the desired load. Just look at modern engine designs today. We have a predominance of long yet relatively small diameter head bolts. You’ll also notice that on the good designs all the bolts are the same length. This makes only one engineering exercise to do rather than two or three as a tightening theory is developed.

Now, let’s look at the other side of this equation. Our head bolt will be pulled or stretched further than the installation dimension because of the thermal expansion rate of an aluminum head versus a steel bolt. This can be an issue, especially with a fastener installed at the threshold of yield and a gasket that doesn’t relax (Multi-Layer Steel).

On a typical cylinder head operating at 250ºF, the head bolt will stretch another .005″or so as the engine reaches operating temperature. This will often result in the fastener being moved significantly farther into the post-yield zone. Repeated movement of the fastener into the post-yield zone can ultimately lead to work hardening of the fastener and sudden failure. You may remember the 2.5L GM engine with a head bolt near the exhaust manifold that broke during service. This was a prime example of this problem.

 

The heads most certainly do tent. Every time I have had a head in they have commented on how they were tented.

I WILL NOT re-install a 6 liter head (really, most any head) without having it surfaced.

I think there are a lot of people that get lucky just pulling the heads, cleaning them and putting them back on but my experience has been that they should always be machined.

 

Thanks for adding Chris.

I too think that is why we see the repeat failures. I take Ford's 0.002" not as the limit to be OK, but the point where they start to fail.

 

So when we install studs for a performance application, we are typically torquing them higher than the factory numbers, since that's possible without going into the yield range for the ARPs?

 

You could, ARP is targeting the typical clamping load for the strength of the stud, which is the tension range of the OE TTY bolts. But keep in mind that with the torque methods, not matter how slippery the ARP lube is, the elongation is still not as precise as TTY. And the studs as hardened, have a narrow deformation and ductility range. Without having an Instron at your disposal, you have no idea where you will end up in tension when the heads heat and expand.

The fastening specialist, and every manufacturer has that position, has the tools to know that and determine the clocking of each fastener, 180°, 270°, whatever. We have trial and error. But 10% higher in torque. I would expect to keep the stud in the reusable range.

 

Consideration: I remember that we used to scrape the slideways of machine tools (lathes and milling machines (I don't know the exact designation in English). What about the idea of scraping the heads 0.05mm/0.002" convex?

 

It's not a simple curve. The heads' ends with the edge reinforcement stay flat; that's visible in the lapping heads video. It's the gasket's job to compensate for this to some degree. The FelPro gaskets are thicker in the fire ring, while in their video they did not delve into it (maybe propriety?), I can see with their history in the aftermarket and drag racing would know to compensate. They said they took some time to develop the gasketI've found several people who have used the FelPro gaskets and have not had repeat issues. But for me, that will depend on the head casting. Stainless o-rings carved into the heads deals with this to a more exaggerated extent, and people do not seem to have issues.

It's easy to mill a head flat, and as I did, it easy to lap a head flat following the engrained bow in the head that occurs after machining and time. (Not the tenting aspect, the longitudinal curve across the intake ports due to the lack of reinforcement at the head bolt stanchions, IMO). So from my perspective, it easier to let the gasket or o-rings do its job and keep a flat head rather than trying to machine or hand scrape a complex bow to the head. Plus, hand scraping is a skill that most machinists do not have and would take an extraordinary amount of time.

 

Hi Jack,
Been meaning to add to this thread but have been busy closing down the cottage up north(out of internet service) and finding out that my 85 year old Dad's dementia is progressing more and more so Mom REALLY needs assistance.

I really think you are onto the real problem associated with the 6.0 HGs with what you describe as "tenting" and that this miniscule "tent gap" is the weak point and the root of a lot of our 6.0 issues.

I was firmly in the camp that if you had a HG problem and you installed ARP studs the problem should be in your rearview mirror. I also think this is why some owners repeatedly had issues after replacing HG sets after HG sets. I still believe that the ARP studs are better than TTY bolts but I think they get a bad rap where in a lot of cases they would work just fine. My concern is with most guys using a standard torque wrench I question the accuracy and more importantly the REPEATABILITY of this torque wrench. Just because you hear the click is it at the same number or are you getting a variance.

Keep in mind my brother's 2003 CCSB still has the original TTY bolts/HGs, gold coolant and EGR and has 255000 miles on it and is a daily driver

Hartwig- Good idea on introducing a .002 convex onto the heads but I would not want to scrape that by hand.Machining flat would be a lot easier. I used to do a lot of machinery way scraping about 15 years ago. First I would need t create a master to scrape to and my second fear would be maintaining this convex shape parallel along the length of the head. Any out of parallel may introduce weak points which may cause another HG issue.

Would it be better to precision grind the heads flat instead of milling them?

I have been reading these threads intently as I myself am finding that my 6.0 may have a possible HG issue but I will start my own thread to keep things separate.

Rob

 

Rob, sorry to hear about your Dad. There were days when I took care of my mom that I sat directly across from her; she looked like my mom, but I felt I just went deep into a twilight zone episode. It takes a change of attitude on the well-minded person's part that the loved one is now tripping, and the care just became a whole lot of work and attention. If one thought handling a kindergarten classroom was hard, wait for the elderly parent. My wife used to say she could see my face aging by the day. I'd agree.

It's always good to get your perspective.

I'm working on 3 to 4 videos about this at the same time, maybe combining. I just deleted something that took two days to do as I thought it would be more confusing. Somehow we went from needing two more bolts to deciding more clamping force will take care of it. It won't, and I got a group of posts from the org where there was a good thread. These bolts are not excessively stretching unless there is a lost coolant overheat, just like every other vehicle.

Trying to contour the heads would be a nightmare, and there is no saying that would truly fix the movement anyway if we have a moving deck. The o-rings are probably the best solution, but people take them as though they clamp down harder on the gaskets as they look at the head bolt situation. That's not what they do. They also may just make the failure take longer, but if it's long enough, then no issue.

The head gaskets may be more of an issue to all of this, and the heads' design. We may be pre-stressing the heads to failure. But again, it's speculation on my part.

One thing for certain, these heads need to be flat widthwise, lengthwise it does not matter.

There's good contact at the bolting locations.

 

Thanks for the kind words Jack. We are just in the starting stages of changes coming for my Dad and my Mom and we are going help Mom slowly but surely so as not to rock the boat too quickly. Noticed that when we were at the cottage with my parents/different setting Dad was confused. It seems the best thing is to maintain a routine/same house they have lived in for 43 years.

If the HGs may be an issue would it be better to use the Felpros which if I remember correctly from your previous research were slightly thicker? Or would this just prestress the heads even more.

I do agree that the heads need to be flat width wise but I was wondering about achieving a better surface finish by using a large flat grinder in the shop instead of the usual milling procedure.

 

It's a tough process for everyone from my one experience: good and bad days or weeks. From my experience, a day-to-day stable environment brings less confusion. I scanned every picture I could find from her home, from her childhood, college, her parents, family, and put that all on a thumb drive and make a loop on her tv. It seemed to provide an anchor, even though there were times she thought I was brother or father. In the early stages, I took her to Brooklyn, where she grew up and worked. I found all the homes, schools, workplaces in her past and drove to all. Something to refresh memories. That was something I should have done before she got too deep into neverland. There were a lot of things I never bothered to find out .... until it was too late.

I was pretty hot about the Fel-Pro's, and in fact, they seem to have had a better run during replacement than the OE. But that is a hard call because you never know how well the heads were checked for flat or the surface finish. As I think I said in both the block deck and head lapping videos, the technical literature and my direct discussions with Fel-Pro indicated getting down to about 10 Ra/60 Rz was a very good thing to do. Measuring the stainless sheets within the gasket assembly, they run about 8 Ra or better.

BPD did a writeup about the differences in gaskets, which was pretty good. I'm afraid I have to disagree with a few aspects, and they missed some details I feel are important to distinguish the Fel-Pros. The fire ring is thicker, BPD says 0.002", I say more like 0.003". My consternation that I just realized is that it may present more of an issue. But there is a way to McQuiver around what I perceive as may be a problem. I would really need strain gauges to prove that theory, but setting that up would be working towards hundreds of dollars in investment. It would have been a no brainer at work.

But yeah, the chart I used in both of the mentioned videos, the abrasive processes are easier to achieve the lower surface finish. But to the machine the heads flat requires a good amount to be taken off the deck. In contrast, my lapping only takes around 0.0005" if your willing to spend a lot of time. But there again, we get to measuring how flat widthwise the heads are. My case was minimal, so I could spend a day lapping. A set of heads out by the worst-case 0.002", you are going to have to cut deep due to the cupping the heads want to do. What I just removed from the one video would have shown that, but I would have lost the point I was trying to make.






This is such a whacked situation. These heads all develop a swale after being machined. And like many castings, once recut may reset the stress and curve again over time.

A brand new head getting machined to be flat. A waste of time. Plus 0.004" was taken off the deck, which will remove stiffness, to a degree we may not be able to afford, and why Ford and Nav say do not machine.





One of my heads after I did a longitudinal elevation map. They measure flat across the width; not even light shows under the straightedge. Ford stated do not measure lengthwise, measure across the width, changing the tolerance from 0.002 in 2" to 0.002" across the width. You know how much that changes not only flatness but waviness.





Contact checks between the block and head, post-cleaning without lapping to post lapping. Despite the swale, the head clamps flat, no gasket is used in these two examples.

The first example is the driver's head clamped to 120lb-ft; the second is the above head (drivers) tightened to 175lb-ft. Both are the same head to the same position on the block. The block had already been lapped flat.

But if flat, the torque should not matter. With that first example at 0.00075" gap in the center, what would it look like if it's close to 0.0020", the no go point according to Ford? And how many heads were bolted up in dealerships at 0.001 to 0.002"?





They are tenting in the center, and bolts will not take care of that. Gaskets do take care of that, but not if the heads keep moving and losing the gasket's compression in the center. Once the compression is reduced, the gasket sealer will start to fret.

I forgot to mention earlier that you stated the variation in torque, but the OE head bolts use the Torque to Yield procedure, a preset torque to compress the gaskets, then angle to a specific stretch. The ideal tightening procedure with a wrench as force is not used as the measure; rotation of the screw thread is. I wish ARP would have done that.

 

Jack, suppose you have a newly machined head. Do you think it will warp when it's o-ringed?