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WWDiesel:
Perhaps great minds do not always think alike, (for those reading along, this is a carryover joke from another thread).
I do not recommend ARP head studs. The reasons why are written below and can be sent to anyone who asks via e-mail messaging as a Word Document article....
REGARDING THE ARP HEAD STUD ISSUE:
Automotive Racing Products, (ARP), DOES NOT recommend the use of their products in the CRD engine as they have not done the research themselves to see what works and what does not for this specific application. The reason you see "kits" available through parts shops like Sasquatch Parts and I.D. Parts is that those kits are put together by ARP as specified by those shops; no warranty is implied or offered. The only criteria used to make up these kits is by identifying exactly what size, length and type of thread ARP studs would be required. No testing had been performed to the long-term effects of using ARP studs by ARP technicians and engineers themselves.
Don't believe me? Here is ARP's Order Desk and Technical Support number... 1-800-826-3045; their main sales/marketing number is 1-805-339-2200.
FOR THE RECORD, I AM NOT BASHING THE QUALITY OF ARP PRODUCTS, THEIR TECHNICAL SUPPORT OR THE COMPANY ITSELF; INDEED, THEY MAKE OUTSTANDING PRODUCTS. THE PROBLEM IS THAT THE APPLICATION IS INCORRECT AND THE RESULTS ARE LONG -TERM PROBLEMS FOR YOUR NON-COMPETITION ENGINE THAT HAS ALUMINUM HEAD/IRON BLOCK ARCHITECTURE. PLEASE READ ON FOR A FURTHER EXPLANATION...
The PRIMARY target market for ARP is performance/motorsport competition; not every day or even commercial use. We are talking racing engines here; where modifications are performed on engines to make them produce 2, 3, and even 4 times the original amount of power the engine was designed to produce; using 2, 3, and even 4 times the amount of fuel and air that a stock engine would. This creates tremendous pressures on competition engines, and incredibly strong fasteners are required to keep those engines from flying apart. Therefore, holding the engine together during racing or other motorsports competition becomes the first, second and third priority; in other words, the ONLY priority. The incredibly strong ARP fasteners, by the very fact that they are so incredibly strong, completely dismiss other necessary requirements for accommodating aluminum head/iron block architecture.
What do I mean by this, you might say? Well, there are indeed other factors at play when you are talking about cylinder heads and proper integrity with the engine blocks they are bolted to. Thermal expansion/contraction and pressure changes occur during normal engine operation; control over these must be maintained while maintaining cylinder head gasket integrity over the long term on normal and commercial engines. People want their grocery-getter and boat hauling engines to last a long time. Cylinder head gaskets fail and cylinder heads warp or crack due to a number of factors, most of which are listed below…
1) Temperature differentials in the metal that is warping or cracking. The more radical the temperature differentials, the greater the chance of the metal warping or cracking.
2) The closer the proximity of the temperature differentials are to each other, the greater the chance of the metal warping or cracking.
BOTH of these facts speak very loudly to the reasons why you preheat an engine before putting a load on it. This is trucking 101; every trucker or commercial operator who has to pay to maintain their vehicle preheats the engine before putting a load on it. Truckers always have their truck engine block heaters plugged in and turned on in the winter, or they have invested in a Webasto coolant heater to pre-heat their engines before starting them. Once started, they go and perform a pre-trip inspection before driving off. By the time the pre-trip inspection is finished and the paperwork is done, the engine should be about 1/2 way to full hot. Then the driver eases away gently and works the engine lightly until it is fully warmed up.
Ideally, pre-heating an engine should be done by an external heater, be it a powerful electric engine block heater or a diesel fuelled engine coolant heater before you even start the engine; you end up with elevated temperatures that are EVEN throughout the engine and that are much closer to the operating temperature when it is working. However, even idling the engine to warm it up is better than some of the dumb-ass things I have witnessed. I have seen videos of guys starting their engines in very bad conditions. Those cold-start contests I have seen are really, really dumb. The same can be said of people starting their engines and putting their foot into it, (often hard), before the engine is even slightly warm. I would not be surprised to see engines treated in the manners described above to have a severely shortened life.
3) The number of times the engine goes through a heat cycle from cold to fully warmed up. The more heat cycles an engine experiences in its lifetime, the more times there are temperature differentials in areas that can warp, like the cylinder head around the exhaust ports.
The number 1 area of the engine that is going to warp is the exhaust port area of the cylinder head, which is BY FAR the area that experiences the greatest temperature differentials. The warping that can occur here can be bad enough that the exhaust valves are no longer aligned properly on the seats, and end up striking one side of the seat more than the other. This can weaken the valve and eventually cause it to break. Forget about the whole narrative about the valves in the CRD engine being of poor quality; severe head warpage is the real cause of premature exhaust valve failure.
4) The final issue that contributes to a cylinder head gasket failure, cylinder head warping and cracking is the use by manufacturers of aluminum head/iron block architecture. I personally do not like aluminum head/iron block architecture for precisely the reasons I am about to describe; it is a significant exacerbating factor to cylinder head gasket integrity and head warping/cracking. Give me iron head/iron block architecture any day over what we have here for the CRD engine.
The thermodynamic properties of aluminum and of iron are quite different, and this contributes greatly to head gasket problems and cylinder head warpage. Aluminum has about twice the thermal expansion factor of iron. Take exact same sized cubes of aluminum and iron, measure them at room temperature and again at 300 degrees Fahrenheit; you will find that the aluminum has increased in size twice as much as the iron has, (that is to say, the amount of the expansion of the aluminum is about twice the amount of expansion of the iron). This creates interesting challenges to engineers wanting to have an aluminum cylinder head properly bolted to an iron engine block that will have permanent, leak-free combustion chambers.
The thermodynamic differences between aluminum and iron are the whole reason why torque-to-yield bolts were created. TTY bolts allow the aluminum cylinder head to properly expand more than the iron block underneath it during operation of the engine, all while maintaining sufficient clamping force to seal those combustion chambers. These bolts stretch a little to accommodate that expansion, and will then shrink down after the engine has cooled off. TTY bolts also act as a sacrificial part when the cylinder head starts to warp; they will stretch beyond their limits and allow the head to warp.
When this happens, you will find upon tear-down of the engine that many of these bolts are barely on, and this has led some people to believe that the TTY bolts are junk. Nothing could be further from the truth… It is much preferred to destroy the bolts and have the cylinder head warp than it is to use a head stud that is so strong that it does not allow the head to properly expand during normal operation or stretch beyond its limits to allow the head to warp if that is what is going to happen. If you were to use such incredibly strong studs, the cylinder head will likely end up cracking and becoming useless junk, (or, incredibly expensive to repair).
It is all about what is less expensive to replace and repair; relatively inexpensive TTY bolts and milling the cylinder head mating surface flat; or replacing a whole cylinder head that has cracked. It doesn’t take a lot to find out that it is the latter that is much more expensive, not the former. Using ARP head studs will greatly increase the chances of the cylinder head eventually cracking, all while doing nothing to prevent a cylinder head gasket failure or the head warping at all.
I can practically guarantee that the O.E. torque-to-yield bolts are not the problem, as suggested to by several LOSTJEEPS.com members.
You may criticize this write-up by explaining that ARP head studs are used all the time in aluminum head/iron block racing engines, and you would be correct. The operative words here are “racing engines”. The common theme of all competition engines are that they do not last very long before they either need to be rebuilt are they catastrophically fail. As such, they simply do not go through nearly enough heat cycles for head warping to become an issue before there is major servicing performed or a rebuild done or there is a major failure.
Racing engines are started, allowed to fully warm up before heading to the track, and are then driven very, very hard so at no point during the race the engine is anything other than blistering hot. When the race is over and if the engine has not catastrophically failed, the engines are allowed to run relatively gently to allow them to cool off slowly, and then they are shut off and the oil changed for the next race. Repeat perhaps as many as 5 or 6 more times, and then it gets torn down for major servicing and/or a rebuild. It is very unlikely that a head warp or head gasket failure will occur during this period of time unless there is a cooling system failure/overheat event or there was a mistake made in building the engine.
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