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also I don't understand why someone would buy a used original part on ebay for 5 times what a repro part would cost because once it is installed nobody knows the difference. case in point, a C2 shifter boot.
You should have seen the crack on the #7 rod on my '63 SHP that Magnaflux revealed - right across the bolt seat - made me a believer in either thorough race prep or higher quality aftermarket rods for high revving engines. These were the early versions that lack the additional material adjacent to the bolt seat that I consider to be useful for nothing but paperweights. The next excursion to 6500 may have broken the rod and taken out the block. That rod was a failure about ready to happen.
Barely a year earlier a fully prepped rod on my E-production TR3 took out the block. This failure may have been initialed by a bolt breaking, which were replaced at the last annual overhaul after the rods passed Mag.
IF early 327 rods are Magnafluxed, which requires the bolts to be removed for proper inspection, which requires new bolts, which requires resizing, they are barely okay IMO for use in a 250 or 300 HP engine, but the cost will begin to approach the price of a set of significantly stronger aftermarket rods. I consider the later design - with the additional material adjacent to the bolt seat - to be okay up to 6000 revs, but only if they pass Magnaflux, so you're back to spending at least half the cost of a set of 8000 RPM racing rods.
A buddy who drag raced a '60 with a 327 had one break. It "only happened" on the street at 30 MPH, but it took out the block. And I have lots of other anecdotal evidence and stories about busted 327 rods. A busted rod can take out the block at idle speed!!!
Nowadays aftermarket rods is the way to go, but there were fewer choices in the seventies, and they were very expensive, so Magnaflux including full race prep and shotpeening was okay if you could do all the grinding yourself.
Today, five hundred bucks is cheap insurance for an original numbers matching 870 block.
The mechanical lifter 327s I've system engineered (all original exterior parts and appearance) make usable power to a little over 7000, and I've told the owners to feel free to rev to 7000 as often as they like, with 7200 as an absolute not to exceed redline with the OE 068 valvesprings. With Crower Sportsman rods and the SHP oiling system, there is nothing to worry about except to not let the oil level get low. Add in no more than half-quart increments as required.
the routine on our sbc after the drag season was to trash the rods as our engine builder said you could magnaflux them till hell froze over but you still won't know how tired they are. pretty tough to throw away a $600 set of Carillo rods.
So hard that most guys don't. They take them to Super Chevy Sunday and sell them to people in the swap meet something like "Only 10 passes - $300 set".
Cyclic loading leads to fatigue failure and most failures start with a small surface flaw that becomes a crack, which then propagates and eventually leads to catastrophic failure and a lot of consequential damage. This is why periodic Magnaflux is necessary for high cyclically loaded parts. Magnaflux won't detect a microscopic surface flaw, but it will detect a crack that subsequently develops. That's why periodic inspection is required in some applications, like certain aircraft parts, but it takes good design analysis and some field experience to develop a suitable periodic inspection schedule for each part.
Because the above mechanism is caused by "surface memory", if you completely rework the surface, such as via shot peening, you erase the previous memory and turn the fatigue clock back if the part is crack free. That's why reworking good used rods is okay for many applications, but it's time consuming and expensive.
IMO a set of used racing rods like those Carillos would be satisfactory for a street engine as long as they pass Magnaflux and have not stretched. If a used set is certified by the seller to have passed Mag, and they have the paperwork to back it up, then I think they are okay to use.
Most materials have what is called an "endurance limit" - the stress at which cyclic loading typically does not cause fatigue to at least 10 million cycles. For most steels it's about half the elastic limit. The early 327 rod section narrows at the bolt seat and then you have the 90 degree angle in the bolt seat crotch. It would be clear to any second year undergraduate ME student that this area suspect.
Chevrolet also recognized that the rod was weak by redesigning it. The second design 327 rods are much superior. That small amount of additional material adjacent to the bolt seats considerably improves their durability, and that's why I think they are okay to use on typical hydraulic lifter engines that won't rev above about 6000, BUT they still need to be inspected on rebuild. To just reinstall them without Mag inspection is very foolish IMO.
For mechannical lifter engines, anything less than a good aftermarket racing rod is taking an inordinate risk compared to the cost of the insurance. Why build a 7000 rev engine that you are afraid to rev over 6000.
See photo below - the late rod on the right has the added material visible on the machined side face adjacent to the seat for the head of the bolt, and the earlier rod to the left shows the concentric machined surface without the "bump" adjacent to the bolt seat.
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