stock head studs reusable?

[gezed]

I have been doing research for my upcoming engine overhaul, and from what I have read, these stock torque to yield/angle torqued head studs can't be used again due to stretching, theres alota debate on this....

So I want to confirm if anyone have reused their head studs or whether or not its a must to get new oem or arp ones.

[blkgtr02]

done it before on my mr2, 2 months after when i put in a new turbo i cranked the boost to 21 psi and head lifted....so iono..for $100 i'd rather have the reassurance.

[nelsonmxmarc]

Not a good idea.

When the word stretch is introduced to any type of hardware, you ultimately assume it's a one-time-use item.

I've been dwelling over the proper torque sequence for the head in the FSM; it turns out the return to 0 after the first step is simply because these bolts stretch. The initial stretch affects the overall torque, while the second torque instruction seats the head studs (10 ft/lbs more) indefinitely. Reusing these bolts is not a good idea.. You're almost guaranteed to see signs of warping.

This is where ARP bolts are handy, as they're reusable and do not stretch, this why 3 even torque sequences across, and no return to 0 is sufficient for torquing the head.

In other words - just buy the proper studs and be done with it. Cheap insurance.

[Terrh]

stock bolts aren't studs.

You can't find ARP head studs for an RB26 for $100 anywhere.

If a bolt survives being torqued without breaking it's still good. If it doesn't, you'll know.

The manual says to replace them every time, but they say the same thing about the main bolts and a lot of people have reused those 2-3 times without an issue.

Personally? I'd probably reuse them if you can't afford the $250+ that a set of studs costs. And if you can afford studs, they're better.

[S13Jordie]

Personally I would wait until you had the funds to replace them. that way you have the re assurance that it was done propper the first time. reusing the stock head studs may be ok or it may cause larger problems in the future.

IMO do it right or do it twice.

[GTRADDICT]

Personally I would wait until you had the funds to replace them. that way you have the re assurance that it was done propper the first time. reusing the stock head studs may be ok or it may cause larger problems in the future.

IMO do it right or do it twice.

+1...

[MarusGTR]

As an engineer, and purely theoretically since I haven't physically dealth with them, I wouldn't.

There's tensile stretch on any studs by their nature, but I'm pretty sure head studs are torqued so that they strain harden in their elastic point of deformation. They are stretched to a point where they the metal's atomic layering becomes permanently affected and if you take the load off, the next time you torque them to spec they can go past their ultimate tensile strength under engine load (aka they can snap.)

http://en.wikipedia.org/wiki/Strain_hardening

[gezed]

yeah Marus, Ive read something similar to what youve described, angle torqued studs are usually torqued beyond the point of elastic stretch to what they call plastic stretch. I also contacted a nissan/infiniti dealer and the guys told me as long as the studs has no visible damage to them, then they should be reusable....but i have a feeling the dont really know what they are talking about

On a side note, arp head studs from what ive read dont need to be angle torqued, the spec was 86ftlbs instead
can anyone correct me if im wrong?

[M13]

and you have to use ARP moly-lube.


I wouldn't re-use ARP studs either. They are meant to be used once and replaced. EVERYTHING stretches and loses tensile strength. To say that they won't is just outright ignorant.

[gezed]

Really? i thought you can reuse arp studs for sure as long as theres no signs of damage cause although they do stretch, they arent pushed to the point at which they are deformed. so when you loosen them again they wont remain stretched assuming that they arent torqued way over the specifications

[MarusGTR]

yeah Marus, Ive read something similar to what youve described, angle torqued studs are usually torqued beyond the point of elastic stretch to what they call plastic stretch. I also contacted a nissan/infiniti dealer and the guys told me as long as the studs has no visible damage to them, then they should be reusable....but i have a feeling the dont really know what they are talking about

On a side note, arp head studs from what ive read dont need to be angle torqued, the spec was 86ftlbs instead
can anyone correct me if im wrong?

It wouldn't be torqued to plastic deformation for a few reasons. Main reason is that plastic deformation weakens the atomic structure and it's integrity; inter-atomic fissures cause the metal to decrease it's ultimate yield. The structure deforms in the plastic domain to diffuse energy from the strain of elasticity, becoming soft and microfissure prone.

Basically take for example people who torch springs; you get one saggy POS spring that makes the car lower because the atomic structure slowly cooled to a softer state, reducing the spring rate.

[nelsonmxmarc]

You can reuse arp studs, because they DO NOT stretch (or if they do it's not detrimental to the characteristics of the metallurgy). Marus summed it up.. Stock bolts stretch, it's the nature of that particular metal. And this is the reason the the head torque sequence in the fsm states to return to 0.. One torque sequence stresses the metal, whereas the following one seats it. Arp doesn't require this, as structurally they remain integral, and arent supposed to stretch.

Different story for conrod bolts..

[nelsonmxmarc]

80 ft/lbs is what arp recommends. The general consensus is to go +5/10 above. I went to 85 to be safe. OEM
is 90 if I'm not mistaken..

[M13]

89ft/lb as per OEM FSM.

I dunno, ARP studs are like 250 bux (not 100, I dunno where you are coming up w/ these prices LOL) and I would think it's a good insurance for building up an engine with a budget in the thousands...


I guess I'm just crazy.

[caliber676]

Your supposed to replace any torque angle/torque to yield bolt if your a decent engine builder.