Used Raceware? Or new ARP?

[jamesjedi]

Hi,

every now and then a set used Raceware connecting rods become available. Would these be better than a new set of ARP?

Thanks for any help!

[lindy 911]

I was unaware that Raceware made connecting rods...

[MBruns]

I would not recommend any rod bolt without knowing the history, both ARP and RW are good quality bolts. But for less than 400.00 new why risk your entire engine to go used.

Mike Bruns

[Walt Fricke]

You must mean rod bolts.

Unless the seller has marked each bolt in such a way that you can consult a list to see what its original free length was, as well as its current free length is, I'd pass them up. If they are so marked, and their permanent stretch is within Raceware's specification for reuse, then you might take a chance if the price is right.

Included in a low price is the potential that you will get only one use out of them. Perhaps these can be used multiple times, but somehow I doubt that all 12 bolts will stay in spec after two uses.

[SCOTITUDE]

Originally Posted by mbruns

but for less than 400.00 new why risk your entire engine to go used.

+1

[911dean]

I would't even consider used. These are really important pieces in any engine rebuild.
Dean

[jamesjedi]

Thanks, and yes I meant to say connecting rod bolts. My thinking was that they may be made of a metal that would enable them to reused. I will buy new ARP.

Thanks for all the help!

[911pcars]

I don't think they're "torque-to-yield-type" fasteners, but you could call and confirm.

Sherwood

[jamesjedi]

Correct me if I am wrong, but ARP is a stretch bolt, while Raceware is a torqued bolt. Not sure whether or not that would affect a decision to go with a used bolt or not? Safest decision sounds like it would be ARP, unless the Raceware is a "super-bolt".

[Walt Fricke]

I think you are wrong. Both ARP and Raceware use steels in the 220,000 psi tensile strength range. Both achieve the needed clamping force well within their elastic ranges. So, all things being equal, both can be reused as long as their post-use relaxed state is back to their pre-use length, plus a very small amount.

I think there may be even stronger steels out there, and ARP may make some bolts with them, but my recollection from perusing their offerings is that they don't make bolts for our 911s out of that stuff.

Any rod bolt can be fastened using torque, or using stretch (if the crank is out of the case). Both can achieve the needed clamping force, though perhaps more care and following a specific series of steps and lubricants are needed using torque.

The stock Porsche rod bolts are often referred to as stretch bolts. This, I think, is a bit of a misnomer. All bolts stretch - if they aren't stretched they won't do their job in any important application. I think "stretch bolt" is used in the sense that the applied torque will (or may, or usually does?) stretch the bolt beyond its elastic limit. That is usually well below its yield or ultimate tensile limit, so the fact that it is into the plastic range does not mean it won't have the needed clamping force. It does mean that it will be substantially weaker if you try to reuse it, so the manufacturer says don't reuse it.

[johndaroza]

stretch bolts are ment to be used one time.

[304065]

Originally Posted by Walt Fricke

I think you are wrong. Both ARP and Raceware use steels in the 220,000 psi tensile strength range. Both achieve the needed clamping force well within their elastic ranges. So, all things being equal, both can be reused as long as their post-use relaxed state is back to their pre-use length, plus a very small amount.

I think there may be even stronger steels out there, and ARP may make some bolts with them, but my recollection from perusing their offerings is that they don't make bolts for our 911s out of that stuff.

Any rod bolt can be fastened using torque, or using stretch (if the crank is out of the case). Both can achieve the needed clamping force, though perhaps more care and following a specific series of steps and lubricants are needed using torque.

The stock Porsche rod bolts are often referred to as stretch bolts. This, I think, is a bit of a misnomer. All bolts stretch - if they aren't stretched they won't do their job in any important application. I think "stretch bolt" is used in the sense that the applied torque will (or may, or usually does?) stretch the bolt beyond its elastic limit. That is usually well below its yield or ultimate tensile limit, so the fact that it is into the plastic range does not mean it won't have the needed clamping force. It does mean that it will be substantially weaker if you try to reuse it, so the manufacturer says don't reuse it.

WWJSD? (That is, What Would Jim Sims Do?)

Jim Sims, were he following this thread (I get the sense that he's involved in some HEAVY engineering projects) would probably say:



(borrowing from Wikipedia), the stress-strain curve of steel looks like the attached. From the origin up to the first peak, that's the ELASTIC deformation region. Elastic deformation means that the bolt stretches, and then snaps back to the same length. Think of this as the elastic in your boxer shorts. The slope of that line is Young's Modulus.

Now, the point labeled 2 in the diagram, that's about where the PLASTIC deformation range begins. Think PLASTIC surgery-- it doesn't quite look the same. If you stretch the fastener past this point, it's going to permanently deform. The further along the curve you go, the more deformation and "necking" down of the fastener you experience until it fails at point 3.

The reason for the two curves is that the lower one is the "engineering" or apparent stress curve, which assumes the load divided by the original area of the fastener. In reality, the "actual" stress curve takes into account the necking down of the fastener and is the load divided by the instantaneous area of the fastener.

Anyway, "Torque to Yield" which I think is trademarked by Mahle Clevite, involves deliberately stretching the fastener past the threshold of yield into the plastic deformation range. This accomplishes a couple things I guess- first, you get the highest clamp load, and second, the strain is very consistent once the curve starts to flatten out. I guess that is also the logic behind angle torque-- you bring the fastener up to a certain point and then deliberately turn it a number of degrees past the threshold of yield, into the plastic deformation range, and you're done. It's hard to reliably measure torque, and hard for folks to measure stretch, but an angle, that's not such a hard thing to measure.

Now I suppose Jim Sims will drop by and tell me that I've got this all backwards