HEAD STUDS OR BOLTS?

Looking for opinions on head studs or head bolts, rebuilding this 3.0 3vze in a 1995 4runner. Is the cost really worth it for head studs or are the stock head bolts adequate?

 

I went with oem. Only 5k on the new rebuild. Time will tell....

 

I have ARP headstuds on my pickup. No issues so far only about 10k on the rebuild tho.

 

This is a very key area for assembly of the 3VZ-E with all the hub-bub about the HG's failing. The thread size is really odd for this engine and I went with ARP studs to set the MLS gaskets in place. Obviously the key to getting the heads set correctly is for a good seal over the entire head gaskets surface area. To do this uniform tension throughout all of the fasteners is important. The ARP head studs have one advantage that is apparent over a head bolt or machine screw as these are actually threaded into the block. The studs are also threaded into the block but that thread is static after the stud is set into the block. Then the hard faced washer is loaded on top of the head and the nut and lubricant is applied to the thread at the nut and stud as well as between the nut and the washer. The torque is then applied sequentially to the nut and unlike the machine screw the twist in the stud is only the drag induced reaction twist by the lubricated thread engagement between the nut and the stud. Where as for the head bolt the twist is applied directly to the fasteners length and the threading is between the bolts thread and the blocks female threaded holes which are different grades of steel. As a Mechanical Engineer I have done a fair number of torque tests and fastener preloading experiments and by far the head stud will produce more consistent tension for the fasteners used in an assembly. Most all of this has to do with the friction in the threads. Once the head studs nut is fully seated and the stud is slightly protruding from the nut the threaded length of engagement remains constant. The same cannot be said for the head bolt or screw as it drives into the blocks threaded hole just a bit deeper with each sequence of the torque being applied. Also the ARP head studs have different threads at the block interface and nutted end of the stud. This is all in the interest of obtaining consistency in the torquing of the nuts. Running the nuts back and forth on the studs to burnish the as manufactured blemishes away is a key pre-assembly effort that can take the torquing consistency to the next level.

If you can justify the expense in your own mind I would go with the ARP head studs if you are going with the MLS-HG's. The basic understanding is that the composite HG's are much more forgiving and therefore the head bolts are good enough. After all that is how Toyota produced the engine.

P.S. The head stud grease ARP supplies is the best stuff to use on your torsion bar anchor nut and bolt. I swear the resistance to set the initial preload on the new ARB/OME bars I replaced the OEMs with seemed like half of what it took to remove them. Again burnishing the nut and bolt with an impact gun with the head of the bolt in a soket and the nut held in a vice I am sure had a lot to do with getting the pair acclimated to each other.

 

Just what atg said, studs provide better, smoother, stronger in almost all applications than a bolt. But, they may be more expensive. One can go with a smaller stud, verses a larger bolt for the same strength (for the same thread pitch/size). There is a lot that goes into fastener technology, but this is a rule of thumb. It has to do with the friction stacking points. The stud has less friction when being inserted in the block, allowing the treads to engage more evenly. The stresses are spread over a larger area as the nut is torqued down.

 

One question, can the ARP studs be used with the engine in place ? If the block is cleaned and the heads are decked.

 

You may have to place the heads onto the block and then thread the studs into the engine and be sure to get the thread engagement right. Otherwise with the studs in the block the head may not be able to be set onto the block and miss the brake booster. I had mine on a stand when I rebuilt it so I am guessing here!

If you are installing MLS you need to hand lap the surfaces of the block and the heads. That means that the alignment sleeves must be removed from the surfaces of the decks.

 

Does anyone know if 7/16-20tpi studs will work in the 3vze block? supposedly the thread is just about the same size as the M11x1.25. The ARP studs are a budget killer.

 

I hear you on the cost of the ARP's but the tensile strength of the ARP's will be unmatched with an SAE inch stud replicant. What is more the nutted end of the ARP stud is not M11x1.25 it is a different metric thread and is probably M12 if I remember this correctly.

 

Arp studs are rated to 180kPsi, McMaster has grade 8 threaded rod rated at 150kPsi. I find it hard to believe that is not up to the spec of a TTY bolt. Plus with a threaded rod I can run the rod all the way to the end of the hole, engage ALL the treads and then cut to length. Using grade 8 pinch lock nuts, like found on rocker arms, would make a pretty good clamp. Its just an Idea.

 

I really do not think you want to hold your 3VZ-E's heads on with all-thread aside from the grade 8 classification! The ARP head studs are studs for a reason and that is to allow for the solid section of the stud to bear the brunt of the tensional strain energy needed to keep the head gasket loaded with pressure from the heads. The tensile strength of all-tread is not going to be the same thing and having the entire length of the fastener threaded is not a good idea because every inch of its length is a potential stress riser. The ARP head studs have the threads rolled into the stud and are not cut into the material like you would on a single point cutting operation on a lathe. This keeps the longitudinal grain structure of the martial intact and helps to reduce the possibility of a failure at the thread to solid cross sectional transition. If your all-thread is thread rolled I would consider it but I bet you will not be able to find that out?

 

This is a classic argument I have with engineers all the time, namely the "is it enough or not" argument. Having been a designer and having to build what designers/engineers have drawn, I can see the sides of each argument.

Example: My spec says the company uses 500kcmil for this run of cable, based on legal, monetary and historical factors. It works with what the company stocks for conduit, switches, terminations, etc. It works fine with a failure rate within tolerances, and historically have a proven track record.
The engineer says that 500kcmil is too small because their spec book and NEC and local codes point to 800kcmil. But the company doesn't stock 800, it won't fit in the pipe, no-one has terminations in stock, it costs tons more, etc.
Each viewpoint/spec/design has merits, and depending on whose spec one looks at, both are correct. Will 500kcmil work for the application? Is 800kcmil better/more reliable? Who made the specs and why? NEC or NESC or G.O.95/128? They ALL would spec the design differently (I have had to argue for each one).

So, is 150kpsi enough to hold the heads in place, considering fresh surfaces, modern head gaskets, even torque? Maybe.
I''m not going to find out, because I have a set of new head bolts that came with the car from the previous owner, but I bet it would hold just fine, because the strength of Grade 8 all thread is *probably* as good as the TTY stock head bolts originally designed/spec'd. TTY by design is stretching the metal, and relying on the strength of the threads and the junction of the threads/shank to achieve clamping force. A stud/all thread distributes clamping force over more threads in the block, but relies on the nuts threads and shafts tensile strength for clamping force. Better? maybe. Maybe not. But I can see it working just fine coming from a lot of years field observations and wrench spinning.

 

This was fascinating to read!

 

@atgparker knows his stuff. Rolled threads are always stronger and way less prone to stress riser cracking at the thread minor diameter.