Torque values, head size

[FEDER]

I have some ARP SS  6 piont bolts to replace the the factory ones for the side cross bolts on My 427. My question is, would the torque be the same for both 3/8" bolts. The reason I ask is because the factory bolt has a 9/16" head and the ARP has a 3/8"  Thinking of leverage the larger head would have over the smaller head. The torque wrench doesnt know the difference but the bolt would. What would the difference be if so between the two.

[Heo]

The leverage is from center of the bolt/socket drive on torque wrench the headsize don't affect that
the torque of the bolt depends of the tensile strength of the bolt

[CaptCobrajet]

I would recommend at least a grade 8 bolt for the crossbolts.  Stainless has a low carbon content, comparatively speaking.  Stainless is "harder" than regular grade 2 stuff, but it doesn't respond well to heat treatment, so grade 8 fasteners can have double the tensile strength of stainless, depending on which stainless.  Most stainless also has low amounts of molybdenum.......this gives bolts a "self lubricating" property, hence the reason that stainless easily galls if not properly lubed.  In my opinion, stainless should be used in submarines, and low-stress, light load places just where you want something to look "purdy".  Just my opinion.....Your stainless will stretch before a grade 8, so the torque value would be lower, and clamp strength would be less.  Generally speaking, the higher strength bolts corrode mutch more easily, but internally, should have no problems, and have a better tensile strength.

[cammerfe]

ightYou might want to talk to ARP regarding the torque capacity of the bolts you have. Hard SS bolts ARE available. It's not as if you need so many that the cost would be outlandish if you were to decide to buy others to suit your purpose, if what you have won't work.

KS

[Barry_R]

ARP stainless claims a strength value just a hair below their normal 8740 fastener - so comparative strength is not an issue as long as you stay within the ARP brand of parts.  The alternate hardware store quality stainless stuff is a whole "nether deal" and should be avoided on any stressed fastener.  I don't think I have ever had a problem putting stainless into an iron or normal steel thread - but running a dry stainless fastener into a dry stainless thread seems to be a recipe for binding and breakage - examples would be going into a help-coil on a cylinder head exhaust or intake.  Smearing a good layer of anti-seize seems to reduce or eliminate the issue, but its still probably "not technically right".

When looking to highly loaded fasteners make certain you stay with some sort of name brand stuff sourced from a known industrial supply (Fastenal, McMaster-Carr, Grainger) or ARP, or similar.  The fasteners in the bolt aisle at the hardware store or big box retailer (I got a deal - they are sold by the pound!) are pretty much a grab bag in terms of quality.  Seems that the Chinese are perfectly happy to put six little lines on anything from any material.  I have had those cheap bolts break off with half the torque they should handle - or never reach any sort of torque before you can feel them stretch.

On street builds I do not think you can ever go wrong using clean unrusted factory Ford fasteners in any location other than the rod bolts (which get cycled out).  I will normally want to use studs on rockers as a matter of preference - far easier for assembly.  Same deal applies on studs - few have any kind of source or strength marking, thus ARP is the only choice for anything that will see a load.  Save the threaded rod for the air cleaner or something - although even a broken valve cover bolt will wreck your day.

[My427stang]

No need to add to anything more than a slap on the table to what everyone else said, for crossbolts, Grade 8 or better and torque them up to stock specs and you could go more if the bolt needed it.  I will add that although they are fixed spacers and shouldn't change bearing shape much from 40 to say 45 ft lbs, I'd torque them to whatever the mains were when they align honed.  If you don't know, stock works. 

Those bolts will want a big stock style washer I think too, the small head may need it even more depending on the shape, and finally, my opinion is that there isn't a lot of tensile strength-type work a crossbolt does, I think it just helps with cap walk and diffusing harmonics into different areas of the block, so if the bearing shape stays good after you torque it, nothing leaks oil, don't lose any sleep

[FEDER]

Thank You all for the replys. I will go back with some factory style grade 8 bolts. BUT about My question on head size wouldnt a large head bolt produce more torque than a small head bolt. Picture a 3/8' bolt with a head or a allen head. Wouldnt the hex tighten the shank a bit more than an allen if both torqued to 40 lbs. It just seems to Me a hex would be tighter.

[Heo]

no it wont take for example 40 feet lbs it is the torque you get if you have
a feet long wrench from the center of the bolt and pull the wrench with 40 pounds

[jayb]

Heo is correct, the size of the head on the bolt, or allen bolt, has no impact on the torque that is applied.

[FB]

Thank You all for the replys. I will go back with some factory style grade 8 bolts. BUT about My question on head size wouldnt a large head bolt produce more torque than a small head bolt. Picture a 3/8' bolt with a head or a allen head. Wouldnt the hex tighten the shank a bit more than an allen if both torqued to 40 lbs. It just seems to Me a hex would be tighter.

your confusing the torque measurement, which is measured at the fulcrum(center of the rotation)

think of it this way:
you have a bolt you can't break loose, so you put a pipe on the end of the wrench for leverage, the pipe doesn't lessen the torque required to break the bolt free, it just makes the force needed to achieve that torque easier, as the lever gets longer, the force required is less to achieve the same torque at the center of rotation.

[Falcon67]

As above, torque value would be the same, or as suggested by the bolt suppler.  And never install any fastener dry IMHO.  I use the ARP lube on just about everything, except SS header bolts into aluminum, then I use anti-seize. 

[Jim Comet]

I only use ARP lube on ARP bolts. It changes the stretch because it is slipperier. I learned this because I used ARP lube on factory Ford head bolts and shortly after I started running it I had 2 broken head bolts. Use motor oil or such on run of the mill grade 8 bolts. Jim