A question about bolts

[sickquad]

Some of this information is wrong. The pitch of the thread will dictate the forces. This is due to the angle of the threads. Think of the reaction forces on the threads from the different angles.

Also, the grade 5 rumors are true for certain types of loadings, maybe impact loads. Where a grade 8 is more brittle and will snap and a grade 5 will bend. I think this is because of the E value.

Look in a Machinery's handbook, available at Barnes and Noble. It's all in there.

-Chris

 

[Triaged]

[ QUOTE ]
Some of this information is wrong. The pitch of the thread will dictate the forces. This is due to the angle of the threads. Think of the reaction forces on the threads from the different angles.

Also, the grade 5 rumors are true for certain types of loadings, maybe impact loads. Where a grade 8 is more brittle and will snap and a grade 5 will bend. I think this is because of the E value.

Look in a Machinery's handbook, available at Barnes and Noble. It's all in there.

-Chris

[/ QUOTE ]

Sorry but it is actually you that is in error.

From "Machinery's Handbook" 26th ed.

Fi = .75 * At * Sp (for reusable bolts)
Fi = .90 * At * Sp (for permanent bolts)

Fi = Preload (in pounds)
At = Tensile stress area (found in charts)
Sp = Proof Stress (depends on grade of bolt and is normally 85% of the yield strength)

The formula that relates Fi to Torque is

T = K * Fi * d
T = Torque
K = Constant from chart
d = nominal bolt diameter

The "K" value is the same for fine thread and course threads!
Black K=.3
Zinc K=.2
Cadmium K=.16

Grade 5 Strength
proof = 85,000 psi
tensile = 120,000 psi
yield = 92,000 psi

Grade 8 Strength
proof = 120,000 psi
tensile = 150,000 psi
yield = 130,000 psi

The grade 5 bolt will have bent and broken before the grade 8 even starts to bend!

And last but not least the "E" value for ALL STEELS is substantionally the same at around 29,000,000 psi.

 

[BranndonC]

so is Grade 8 ok for head bolts? i assume not, but i cant seem to find head bolts anywhere local and i'd have to order them and have the shipped

 

[diesel4me]

Head bolts are special,not just the grade of steel,but they are shouldered near the head,and narrower near the thread than a standard bolt--I recently bought new head bolts for a small block from autozone in Fel-Pro brand,they had them in stock and cost about 35 bucks--if you have a speed shop near you they might have ARP or other similar ones available--if not,your local GM car dealer parts department will probably have them,but at a premium price!. /forums/images/graemlins/crazy.gif

 

[BranndonC]

they are for a 500 cadillac motor, should i try a GM dealer or a caddy dealer?

 

[ntsqd]

Have you tried ARP for Cad head bolts? Larry Krusik has probably already gotten them to make some for him. So even though they may not catalog them, they probably have the dimensions to make them.

FWIW It may have been me that stated to use a larger G5 instead of a G8 bolt when it's critical that the bolt not fail. Since G8's are not as Ductile as G5's it makes sense to use a G5 in a place where loss of the bolt would be catastrophic. The thing you HAVE to remember is to increase the size of the bolt to gain back the needed strength in the joint.

The best solution is to go to a better quality of bolt. Socket Head Cap Screws ("Allen bolts") have BOTH better tensile strength and Ductility than a G8 bolt. Be sure to use an AN type washer under the bolt head, unless in counterbore intended for a SHCS, the washers are NOT optional.

 

[hawkeye649]

[ QUOTE ]
This may be true--I have broken a few grade 5 and 8 bolts on my plow(the pins that hold the plow to the plow frame)and all I could get at that late hour was cheap grade 2 bolts at home depot--I hit a few obsructions during the duration of the storm,and I thought sure the bolts would snap(they were 3/4 inch x 6 inch)but the next day I checked them--they looked like banannas,but they didnt crack or break!I know stainless steel bolts are not good for a lot of automotive applications,they dont rust but they seem to be brittle,and dont like heavy shock loads,I tried stainless steel studs in my exhaust manifolds once thinking I;d never have to change them again--WRONG! the next time I went to loosen them,they snapped off like peanut brittle,I had to pull the manifold and have them removed at a machine shop with an end mill--none of my drills would even scratch them /forums/images/graemlins/angryfire.gif. I use cheap carriage bolts or threaded rod for exhaust studs now--they wont be useable again anyway,gaurenteed to break off,but at least they drill out easy. I also put a new front suspension crossmember in a friends corvair,he pirated all stainless bolts from his workplace,we snapped 3 of them just tourqing them into place--we decided they werent the hot setup for shock mounts and suspension bolts,and ended up buying grade 8 bolts from the hardware store.I have noticed that grade 5 and 8 bolts corrode much slower that the cheap grade 2 stuff--maybe better coatings on them,or just better steel?. /forums/images/graemlins/crazy.gif

[/ QUOTE ]

Ever notice how your father's uber old tools just surface rust, MAYBE slight pitting? Or how a nice *american* firearm, say a colt 1911, will just surface rust? I attribute it to the carbon content & or quality of the steel. That is why I would say grade 8 rusts slower. /forums/images/graemlins/thumb.gif