The Ford Barn - 5.5 head

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- Model A (1928-31) (https://www.fordbarn.com/forum/forumdisplay.php?f=3)

- - 5.5 head (https://www.fordbarn.com/forum/showthread.php?t=330421)

Quote:

Originally Posted by ModelA29 (Post 2252635)

New grade 8 studs have a much higher yield rate than the originals which were probably grade 5. They all rely on some stretch for their holding power. The grade 8 stretches less so it doesn't fatigue as fast. Most newer cars torque the heads 90-100 ftlbs and at 55 lbs the grade 8s should last many rebuilds. Has anyone tried 55+ lbs with the new bolts? My 289 HiPo would blow the gaskets at the stock torque but 5 pounds extra and the problem was cured.

I presume when you said “bolts” you meant “studs”. I have a 5.5 head and replaced the studs with the high strength when I replaced the head gasket a few months ago. I’ve torqued the head to 65 ft-lb four times now, and each time fewer and fewer of the nuts move. This is a combination of the gasket finally losing its resilience plus stud stretch. (I use the Best graphite gasket #509 plus copper spray). This is the third engine I’ve used the high strength studs and the Best 509 on, quite pleased with that combo (the other two had 4.2 heads so only torqued to 55). I will likely use these same studs and gasket on my Burtz build with the 6.5 head.

When you increase the stiffness of the studs, the threads in the block see higher tensile stress, so their fatigue life goes down. What follows may hurt your head, but these are some of the considerations a good engineer accommodates in a joint design like a cylinder head attachment

Here are some pointers about studs: (1) Note that one end of a stud has coarse threads and the other end has fine threads. The coarse threads generally have less tensile strength but there are more coarse threads in the cylinder block to distribute the load. The head nut has fewer threads, so the nut end of the stud has fine threads that provide more threads per inch to carry the load; (2) Bolts have have stress risers such as the transition of its head to its shaft, so the distribution of load from torquing a bolt to get a certain clamping force is not as accurate in comparison to a headless stud; (3) Studs have superior fatigue life in comparison to a bolt because the stud is headless; (4) Studs are less expensive to make and heat treat than bolts; (5) The loading of a cylinder head attachment fastener is cyclic, so preload via torque is very important as it changes the alternating stress range in the fastener which has a profound effect on the fasteners fatigue life; (6) Changing the stiffness of a stud, i.e. Grade 5 vs Grade 8, affects the distribution of load especially at the coarse threaded end in the cylinder block. It raises the stress in threads of the block because the stiffer stud does not absorb as much energy by expanding; (7) Stiffer studs increase the clamping force acting on the head gasket.
If your head hurts after reading this post, take one aspirin and relax for awhile in your easy chair.

Grade 5 is your friend. :)

Bob, The modulus of elasticity of steel is about 30,000,000 psi. It does not matter whether the stud is grade 5 or 8. So the spring action in the stud is the same for grade 5 or 8. The grade 8 stud will go to a higher load before it yields. Or it may not yield at all but just break. If you are yielding the grade 5 studs then you are applying too much torque. The Model A studs are not designed to yield. Other cars have studs or bolts that are designed to yield and you will see these studs sometimes necked down. These studs or bolts are one time use and replaced each time.

Sorry Bob, but I had to take 2 aspirins!:mad:

Quote:

Originally Posted by Bob Bidonde (Post 2252766)

When you increase the stiffness of the studs, the threads in the block see higher tensile stress, so their fatigue life goes down. What follows may hurt your head, but these are some of the considerations a good engineer accommodates in a joint design like a cylinder head attachment

Here are some pointers about studs:

(1) Note that one end of a stud has coarse threads and the other end has fine threads. The coarse threads generally have less tensile strength but there are more coarse threads in the cylinder block to distribute the load. The head nut has fewer threads, so the nut end of the stud has fine threads that provide more threads per inch to carry the load;

(2) Bolts have have stress risers such as the transition of its head to its shaft, so the distribution of load from torquing a bolt to get a certain clamping force is not as accurate in comparison to a headless stud;

(3) Studs have superior fatigue life in comparison to a bolt because the stud is headless;

(4) Studs are less expensive to make and heat treat than bolts; (5) The loading of a cylinder head attachment fastener is cyclic, so preload via torque is very important as it changes the alternating stress range in the fastener which has a profound effect on the fasteners fatigue life;

(6) Changing the stiffness of a stud, i.e. Grade 5 vs Grade 8, affects the distribution of load especially at the coarse threaded end in the cylinder block. It raises the stress in threads of the block because the stiffer stud does not absorb as much energy by expanding;

(7) Stiffer studs increase the clamping force acting on the head gasket.

If your head hurts after reading this post, take one aspirin and relax for awhile in your easy chair.

Bob,

My head only hurts when people don’t break up their long posts into paragraphs.

David Serrano

Quote:

Originally Posted by California Travieso (Post 2253021)

Bob,

My head only hurts when people don’t break up their long posts into paragraphs.

David Serrano

And don't use periods, spaces and capital letters.

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