ARP Rod bolts re-use?
 

Are the ARP rod bolts on the M-tuned rods torque to yield? If so can they still be reused? Is there a bolt elongation spec?

Thanks

ARP's website mentions that their bolts are reusable but should be replaced when they have permanently stretched.

To quote ARP's page at : ARP-bolts.com | ARP - World-leading Fastener Technology

" As a rule of thumb, if you measure a fastener and it is .0005˝ (or more) longer than its original length it has been compromised and must be replaced."

If you didn't measure the free length before installation, you need to replace them.

generally if you used them only once you can reuse them, but always measure first. you can also get a reference from arp for their factory length.

Thanks guys. I'll let my machine shop measure and decide. They may even have new arp studs on hand.

ARP is very good, but they aren't this good. I typically see a variance of at least ~.005" from bolt to bolt for length, which is enough to make any published reference length worthless for the OP's usage.

If the bolts don't return to within .0005" (that's half a thousandth) of their original free length, they're scrap.

IMO if your not sure if you should reuse them you probably shouldn't. Goes with the cheap insurance thing.

Sorry to revive, found the ARP part number 118-6401, for replacement stock rods.

For H-Beam forged, ARP part number 200-6209.

Let me edit a little bit; the sheet is for the hi performance, not M-tuned.

Here is a link for the M-Tuned fasteners.

ARP 2000 5/8 1.6

Found this other site, 2000 ARP torque specs

Just in case the attachment does not work.

https://www.miataturbo.net/attachmen...ine=1371996946

The M-Tuned/SCAT/Eagle/Manley bolts are 1.500" UHL, not 1.600. We have them in stock, $70/set.

ARP rod bolts 2000
 

https://www.miataturbo.net/attachmen...ine=1372040411

Info obtained by Emilio 949Racing.

I will check then, I have not torqued them yet.

Meh. I just kept torquing the ARPs headstuds down by 5ft/lbs on my old DSM until the head stopped leaking. Who cares if they were at 100ft/lbs, they held 25 psi + just fine on a daily basis.

It's probably best to replace, but I think you can get by if you're willing to accept the risks.

Torquing ARP head studs past 80ft.lbs on a Miata head is a great way to crack the head. :hustler:

The digital caliper and the bolt hole thru template states they are 3/8...

The bolt head stamp is ARP 2000 -16.

SCAT must be using a different rod bolt, then. I just measured a BNIB Manley rod bolt (ARP2000) at 1.500" UHL.