Originally posted by U1ARUNIT
Alan,
I kept the info you posted a while ago for reference. Hope you won't mind me pasting it in this thread.
Alan's Quote:
Now while I haven't had a bolt or stud come loose (as in finger tight) with any head, iron or alloy, I have seen a significant reduction (nearly a complete elimination) in head gasket failure with the use of retorquing and also with the use of studs.
First, I don't think the commonly suggested overtorquing works (I'm not saying that you suggest overtorquing, just that it is a common suggestion around here). The reason is that a fastener, especially a high performance fastener like an ARP bolt or stud, is designed to stretch a certain amount, and is in fact a linear spring. Now, when you torque a fastener over a head gasket, you stretch the fastener, and preload it like a spring, and there is only so much stretch and spring left, the the fastener will either stop stretching or fail. Since with the ARP we are dealing with a 180,000 PSI fastener, actual failure is unlikely, so when the cast iron head retained by that fastener expands as the engine reaches operating temperature, it expands somewhat faster and to a somewhat greater degree than the fastener does. So, if the fastener is overtorqued and will not stretch, if it is an ARP 180,000 PSI, either the threaded bolt boss in the block will fail in some manner, or the head gasket itself will be crushed somewhat by the expanding block and head. Now you've crushed that gasket more than it was designed to be crushed (it was designed to be preloaded more than actually crushed) and the gasket cannot return to its pre crushed thickness. This removes a certain amount of preload on the fastener, and weakens the joint. Retorquing here is critical.
Second, as to retorquing, many have gotten by without it. However, when we returned to the old habit of getting the engines to full operating temperature and stabilizing them there, NOT making any power runs on them, and then allowing the engine to FULLY return to ambient air temperature, and only then retorquing the fasteners, we eliminated over 95% of all blown head gaskets on all of our engines, both normally aspirated and supercharged, no matter what gasket or fastener was used. Evidently there must be some crush and taking a set on the part of the head gasket itself, since we measured the fasteners to see if the had permanently stretched and taken a set. We use plain old Permatex 2B sealer on the threads of all BOLTS that enter the water jacket, and to date have NEVER, in maybe 400 or so engines built, had a head fastener leak after retorquing. Even Fel Pro reps grudgingly admitted that their gaskets seemed to perform better when they were retorqued. Not all joints will show a need for it if you just try to take a torque wrench and see if the fastener will turn at the final torque setting, we always break them loose to around 70% of the final torque, and retorque them. I've sat through around 20 or so hours of seminars given by Fel Pro and ARP, with experts such as Keith and Randy Dorton, Spenny Clendenen, Lou LaRosa, Smokey Yunick, and a few others, and the story has always been the same.
Third, on the subject of studs. As far as I'm concerned, there can be no legitimate dispute of a few facts regarding the use of studs over bolts in main and head fastenr applications. Fact one is stress on the bolt boss in the block. A properly installed stud will not overstress the bolt boss in a block so long as the proper amount of preload or torque is applied. Once properly installed a stud only loads that boss in a linear direction that it was designed and intended to be loaded in, and it does not have a rotating wedge effect on the threads. Fact two is the preload on the boss and block in question will be the most accurate preload in both force and direction possible. The better quality and finer threads on a stud WILL generate a more accurate preload. The threads and block will be much less likely to be damaged. In the case of head gasket joints, we've seen a measurable difference in the amount of failures. We've also noted a measurable difference in distortion of the cylinder bore and the deck surface. We have not noticed any difference in the need to retorque. If you install the studs into the block in the proper manner, they will not leak. The only drawback to studs is that they inhibit or prohibit in some cases removal of the head in the car. On the other hand, we've found that coolant of any type that gets in the oil in any significant amount especially while the engine is under heavy load will cause some damage to bearing surfaces, and it is nearly impossible to remove all traces of coolant from the oil while the engine is in the car besides in most cases at least some damage will have been done to the bearings, although it may not be obvious to the untrained eye. In other words, in the rare event that we lose a head gasket, then engine, whatever brand and type, comes out and down for inspection. A few hours labor and some gaskets and possibly a bearing or two is much cheaper than a ruined block, crank and or rod due to an oil/coolant contamination related failure.
We always chase the threads (all of them) in a block before final cleaning any way, and we also clean the bosses out with a spray cleaner like brake cleaner or Loctite prep cleaner before installing fasteners. When using studs, we follow the same prep procedure, and then we measure the studs and mark them with one wrap of masking tape to ensure they are installed at the proper depth. Then a pair of clean heads, with no gaskets, is set aside. We install each stud by hand into the block with a light coat of RED #271 Loctite stud and bearing mount thread adhesive, doing it quickly so that the Loctite doesn't set up, and then we place the head on the block, and torque the head to 35 or 40 foot pounds before the Loctite cures, and we let it cure for 24 hours before disturbing them. This will assure that the stud is sealed and is standing straight up from the deck surface. We've not had a single instance of studs leaking when using this procedure in nearly 20 years.
Regarding the use of alloy heads on both iron and alloy blocks. If you look closely at the catalog, you'll note that ARP often makes a special stud for alloy heads. These studs are a special diameter on the shank, to allow them to have the proper amount of stretch and preload for use with alloy heads which have a much much greater thermal expansion coefficient than iron heads. No matter what you do, alloy heads WILL crush a gasket somewhat, and WILL require retorquing, but these special studs do alleviate the excessive crushing, and will result in a much more successful result.
All of this may have been a waste of 45 minutes, it may fall on deaf ears, and I may be branded an idiot, but it has worked for me over a period of around 20 years of racing and engine building that has encompassed everything from small engines running alcohol and nitrous oxide ( a 16 HP Kohler engine with a 356T6 billet head that made 68 HP at 22,000 RPM), to Super Modified pulling truck engines ( 11.5:1 static compression with 50% overdrive on a 10-71 blower will test your headgasket theory well at 7700 RPM), and everything in between. Take it for what it is worth, and use it or call me a fool. Maybe it will help someone, anyway.
-6PacktoGo/Alan Witter
. The Federal Mogul and Fel Pro tech reps told me I should retorque, so did ARP, and so did Smokey Yunick. Good enough for me, and it solved my problems.
