What are the chances that the rod broke taking the bolts with it?

I don’t know anything and I’m just repeating something I once heard, but in going up to 3.2 design, didn’t the factory leave less meat for the rod bolts? I thought I’d heard that stock 3.2 rods are weaker than stock 3.0 and more prone to failure than earlier or later engines?

I’d be interested to hear if this is true or not?

Thank you for this helpful tip. I've been scouring the usual sources looking for usable cases!!

On the surface this may sound like a dumb question - and I don't question that genuine ARP hardware is of a very high quality, and that in building an engine for extremely hard use (such as in racing) nothing but the best should be used - but why shouldn't stock (new) Porsche rod bolts have been perfectly adequate?

Any pictures of the bottom of the rod, or that crank throw?

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Two of the break surfaces look like fatigue failure. Smooth beach then an area of rapid crack propagation. Hard to imagine the rod nuts could have backed off without the piston running into the head, especially with that high compression ratio. My vote is bad or over-tightened bolt(s) on that rod. Could have been just one, as soon as it went the other would be overstressed and fail. If so, only one bolt would show fatigue, the other should show ductile failure. If two clean breaks, then two bad or over-tightened bolts, breakage of one hastening crack propagation of the other.

Dan

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Was it possible to check the torque on the other rod bolts during disassembly?

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John is ( as usual) correct

Subscribed. Sorry for loss.

I'm sincerely sorry for that happened to you mate ,

A friend has been victim of the same break .............it's mechanic , and that happens , even it's rare.

https://i79.servimg.com/u/f79/13/86/10/18/carter10.jpg

For reference



http://forums.pelicanparts.com/porsche-911-technical-forum/64438-rod-bolt-failures-carrera-3-2s.html

http://forums.pelicanparts.com/911-engine-rebuilding-forum/240426-3-2-rod-bolt-help.html

The Carrera rod bolts have been a known weakness on the 3.2 for decades. Original bolts are always upgraded on a rebuild, even if it's a stock rebuild otherwise. ARP or Raceware are the common choices.

Is a shop in Dallas doing the tear down?

Curious about this as well, would like to hear more opinions on shops in DFW. I have heard DC Racing is good, and some others but would like to hear from some actual customers.

Thanks, that's why I asked the question............part of a learning process.

A dropped valve once ended up with a cylinder fracturing and the rod sawing a slot in the case at the spigot in an engine of mine (over rev caused valve issue). The connecting rod cap was distorted so that only the outer ends of the cap were still touching the main part of the rod. So the high strength aftermarket rod bolts were stretched. And bent. And you could see where they were narrowed where they stretched. But they didn't break.

ARP will let you know if any non-ARP bolts were involved. Though given how gently you say this engine was used, I'd have thought stock bolts would have worked, at least until you started putting the pedal to the metal.

Modern engines are able to use higher compression because of better spark plug placement, the use of knock sensors, and the ability of the ECU to change things on the fly based on what sensors are telling it.

Did the shop doing the disassembly by any chance have access to the bolt stretch figures used in assembly? If so, did they check the stretch? This could tell if other rods had overstressed bolts. But since A did the bottom end, and the shop you are using now did not, I don't suppose this was done? Though you could still test for this - measure the unbroken bolts, reinstall them and stretch to spec. Then loosen the nuts and remeasure to see if any of them were stretched beyond their elastic range. This should not happen, so if it does it suggests at least some of these bolts were bad/wrong.

Those main bearings look great. How were the rod bearings? What did the bearings which must have fallen out of the rod with the broken bolts look like? Was the broken rod discolored, as in a lubrication failure or some other issue like wrong dimensions somewhere?

Hey Allan, what did ARP conclude regarding these con rod bolts?

Not sure what you could have done during your 30 foot test drive to a stop sign. However, no telling what occurred during the repair shop's test drive.

If the shop isn't showing any signs of contrition, I would take the engine to an independent shop for a forensics inspection and written report. You could show this to your engine builder and/or an attorney.

It sounds like a rod nut wasn't tightened to spec, but that's just my guess. If detonation was the cause, there should be signs in the combustion chamber and the affected piston/cylinder (e.g. melted/deformed material).

Sorry to hear that.
Sherwood

From what I remember the factory original rod bolts were fine and long as the engine was never over revved with a money shift downshift. I used ARP bolts on my rebuild "just cause" they were not much more expensive.

Sorry for your loss. It truly sucks.

Man that really sucks..... sorry this happened. Please keep us updated on any new relevant info.

He hasnt logged in since March of 2020..