pentaq

With 3/8 ARP 2000 bolts. I tightened them to 28 lbs ft. Sounds right?
I got this value from Eagle but it's even less than stock. I'm confused here.
Does anyone confirm?

Oyvind Ryeng

That sounds quite low. Let's hear what the pros have to say...

PrecisionH23a

3/8 arp 2000 7/16 bolt head 43ftlbs

5/16 arp 2000 3/8 bolt head 28ftlbs

pentaq

OK, let's talk metric

I used 10mm socket to tighten them, so it's ca. 3/8" , because 7/16" is 11mm. Am I right?

An additional question: why is that? Only 1mm of the difference and almost twice the torque?

pentaq

ttt

Mykizism

the two bolts eagle had on their rods are two totally different sizes' u cant go on your theory and come up with arbitrary stuff like that go by what precision said.. what he said is right on.

pentaq

It's not the theory. Just need for confirmation as my rods are already tightened. Better ask and be sure than be sorry. And I have my engine open so far. There's pretty small difference between these rod bolts and their corresponding torque is completely different.

Mykizism

eagle had two sets of rods, with two sets of bolts,

old set used
5/16 arp 2000 3/8 bolt head 28ftlbs


new set uses
3/8 arp 2000 7/16 bolt head 43ftlbs

so which socket did you use to torque the rod bolts. and dont say 10mm.. because thats the improper socket to use in this situation

Mykizism

on top of that, for the tension of the bolt to be proper, its a good idea to torque the bolts, un torque them, and redo it about 3 - 5 times to allow proper rod bolt stretch.. if you didnt do that in the first place, do that and use the proper socket, and go by the torque readings precision gave

pentaq

yes, I say 10mm as in Europe we use METRIC **** not imperial and you're not able to buy sockets in inches without a special order. And it was the closest socket size which fits the bolt head and didn't strip it.
and yes I retorqued bolts a few times as I was plastigauging bearings.

So... why the difference of 1/16 of an inch implifies almost the double torque value?

PirateMcFred

I do not think that it has much to do with the diameter of the actual bolt head. It is a simple axial rotation so the mechanics are the same. I think that the 3/8's bolts have a thicker bolt shank (the actual part that stretches) and when torqued to 80% yield (pretty standard load) there is more clamping force that keeps the rod cap in place. Of course there is also the thread pitch to consider. Finer thread pitch would require less torque to stretch to yield than a coarser thread pitch assuming that the surface finish on each is the same. The assembly lube used makes a difference too. ARP usually has 2 different torque specifications: one with their Moly Lube and another with just engine oil. The moly is more slick so it requires less torque to attain desired stretch.

Pirate

PrecisionH23a

It has to due with stresses, bolt fatique, bolt root diameter vs. tensile strength, and several other factors. All of this is determined through Finite Element Analysis (FEA). This method basically will tell you how a 'component' will react to certain loading conditions. This is basically how they determine the components load failure and rate the bolts for X ksi. Below is a picture of a 3d FEA:





It's quite complex actually.... even though 1/16" seems small it is a MUCH stronger bolt. For example, why is a 10mm bolt on your oil pan only 9.6ftlbs of torque where-as a 12mm is around 18ftlbs?