MTFCA Forum

I am installing the dual exhaust manifold on the speedster project engine. Since I have been unable to find 3/8-24 double ended studs 5-1/2 inch long I am going to make them myself. My question is what material is best. grade 5 or grade 8. I will be taking a 6 inch bolt and cutting off the head and rethread one end. My gut feeling is grade 5. I say that because it will be able to stretch a little and be more likely to keep tension on the assembly. ??

But I have been wrong many times before ....

Any help will be appreciated. Im almost ready to put the engine in the car after 5-1/2 years of work (fun).

Here is a photo of the bolts in question. In the photo, the manifold is held in place with two bolts for the "tall" clamps. I want to switch to studs instead of bolts. The stands are combination intake port plugs and manifold clamp stands that I made last week ....

I always opt to what I rather have break first - the bolt or what it is threaded into. I found this statement in an Engineering reference "In actual fact, Grade 5 bolts are often preferred over Grade 8 . A Grade 8 has a very high tensile strength, but can be brittle. In applications such as suspensions, a very high number of load/unload cycles can produce work hardening, which produces an immediate, or catastrophic failure. It’s often much safer to use a Grade 5 bolt which will bend, thus providing a warning, rather than a Grade 8 bolt breaking without warning. As long as the Grade 5 bolt has been sized large enough to take the expected load, we don’t want to trade toughness (resistance to stress cycles) for the ultimate tensile strength of the Grade 8 fastener."
Grade 5 bolts can withstand 120,000 lbs of tension per square inch of cross sectional area.
Grade 8 bolts can withstand 150,000 lbs of tension per square inch of cross sectional area.

If it were me, I would go grade 5.

I don't remember the exact explanation why, but I was always taught that the end of the stud that goes into the casting should have coarse threads and the end with the nut should be fine thread. The studs should go into the casting only finger tight. If you are going to use threadlocker on the studs in the casting, use a socket or stack of washers and the fine thread nut to hold the stud upright in its tensioned position while the threadlocker cures.

Frank, Acording to what you said, I would want the bolt to fail before the holes in the block. The grade 5 probably would fail before the block. The grade 8 probably would be more likely to "tear" the threads out, than a grade 5.

Mark, I was also taught that a course threads in the casting and fine threads for the nut. The reason I remember is that a fine thread creates less friction amount when removing the nut , than a course thread. Because of less friction or torque, the fine thread will break loose first. So in the case of course thread in the casting, and a fine thread nut, the nut will break loose first. This also transfers all the wear to the nut instead of the casting. That is a good feature of items that may be removed often.

In my case , I will have fine threads in the block and also the nuts. I will need to use thread locker in the block or double nut the studs and tighten them into the block, so the nuts will come off first.
I will probably tighten them into the block. That way I can use anti-seize on the threads.

When I used to work in the nuclear power plants, we were taught. You "shall" "must" "will" use anti-seize on "all" fine thread or any stainless bolts. No exceptions to the rule. If caught not using anti-seize, you could loose your job. So I find it impossible to not use anti-seize on fine threads or stainless bolts on anything I work on.

The structure of cast iron is not amenable to fine threads. Fine threads present more surface area; shallower thread cut reduces stress risers.

Ford specified the material to be cold rolled Bessemer steel, no heat treatment, so the grade was probably about a 2.

If you flip your manifold clamps over you won't need such long studs and you might find long enough studs.

I would order some USA of Canadian made grade 5 coarse thread bolts longer than needed from MSC or another reputable supplier. I would not use Chinese or near east, ie: Israel, Turkey made bolts. I would cut the coarse thread ends so that they threaded area was about 1/16 shorter than the depth of the thread boss. Then whack the heads to get the distance correct, buy a new, sharp die and thread them in the lathe with good threading goop.

But then, I don't like Chinese bolts.

There are also a lot of older American made bolts around on ebay, various industrial salvage sites, etc., if you want to save some money. I have tons of bolts but not well organized. Takes time to go though them and find what I need.

Bolt Depot is an excellent choice for quality, quantity, and grade requirements. Something I would like to suggest is a secondary brace coming from the top of the head bolts would really reduce the stresses that will be encountered during operation. There’s a lot of weight hanging out there. And I am not referring to anyone’s girlfriend either.., wink wink.

Hope this Helps,

Hank

Sure is Pretty Donnie, and it should perform well at higher rpm's with those extended runners!

All the Best,

Hank

is that a '13 block??

Henry, Good suggestion. I will look at adding a brace.

I had some old US made 6 inch grade five bolts. So I cut them off and rethreaded them on the lathe, then I chased the threads with a die nut. Turned out nice. From the input above I think grade five will work OK.

Dennis, I tried turning the clamps over. But the way the clamps and dual cast iron manifold are made, they did not fit well. I would need to grind some of the manifold to get the clamps to fit.

Scott, The block is a 1919. Due to leaking "freeze plugs, and some really crappy exhaust manifold gaskets for a homemade model A manifold conversion, the "freeze plug" seats were badly rusted away at the bottom. So since this is a speedster engine I just drilled and tapped the block for the screw in plugs. I know they are not correct, but it saved an otherwise. good engine

Thanks for the input.

Donnie, your photos show some thread still not engaged when you install the studs. If there is enough thread, you could run a nut on first, run the studs in and the tension the nut as a locker. That will stop them winding out if you ever have to remove the manifold.

Hope this helps.
Allan from down under.

Allen, The studs and bolts shown in the photo above are temporary bolt/studs. The new studs I made, have full thread engagement. I will use double nuts to lock them into place.

Donnie

I vaguely (?) recall your mentioning a long time ago about putting in those plugs. I think it's neat. Thanks for responding and explaining.