The cone-shaped fracture face indicates a tensile failure and I agree with 125shifter, i.e. material is brittle. Since the failure occurred near the transition from shank to head, a stress riser condition (thread root) probably combined with the material condition. Maybe a bad heat-treat lot.

Bye the bye - fastners are never cast. Material properties needed for the applications can't be met with a casting, plus the cost is too high. Most common use fastner shapes are forged, hot & cold worked

Sounds like some confusion over cast vs forged.

All formed material begins in a liquid state. Casting is when the liquid material is poured into a shape (permanent mold, sand cast, etc.) then allowed to cool. The part is then machined or used as is.

Forging is when the still hot material is cooled to a semi-plastic state and hammered to shape before cooling to room temp (improves grain structure), then machined. Forming threads by rolling maintains strength. Forming threads by cutting creates stress risers and invites failure for critical fasteners.

Hope this helps,
Sherwood

I compared a bolt from the same batch with a old bolt from my toolbox and there are some remarkable differences. First of all, the new bolt has no strength reference on the bolt head, only some kind of symbol that might refer to the manufacturer. The other difference which might be the cause for the failure is the depth for the socket. The new bolt is 6.98 mm deep, the old one only 5.28mm (both heads are 8.40mm high). This leaves much less material to take the load.

I am relieved that the bolt failed during torquing. I would have realy been in trouble when this would have happened at 7300rpm, who knows what would have happened then.

http://forums.pelicanparts.com/uploa...1088631591.jpg http://forums.pelicanparts.com/uploa...1088631613.jpg

Like I said earlier............. a wok. That bolt was definetely made in a wok.

And as far as that stamping on the head of the cheap bolt............ Is that a dollar sign? makes you feel really good when you buy a critical bolt like that and all that is marked on it is- $

Thats one money looking bolt , well at least whoever is making that knockoff and selling it to people and sitting back and counting his.

Counterfeit; the parts source owes you a refund. In the US, there is a government telephone hotline to report such instances.
I also believe there are damages, fines and jailtime in the future of vendors who misrepresent such goods and the defective fasteners end up in DOD equipment or aircraft and other critical public safety applications. :mad: Jim

You guys are very quick to judge. Porsche is a company just like any other, and I'm sure that they have "farmed" out many of their component specs to outside manufacturers who have stuff manufactured in Asia. Just because it has that Porsche logo on it, or came from a Porsche dealer, doesn't mean it was made by Hans or Franz in Germany.

The more likely culprit is a lack of quality control from one of Porsche's suppliers. I can't imagine that there's a big enough market for Porsche 911 flywheel bolts that someone would take the time and energy to produce a "knock-off."

Either way, to see this failure is indeed troubling...

-Wayne

Well, I like to see some sort of spec. on a fastener. The right one has it, the left one doesn't.

furthermore, the bottom of the socket on the left one is rough, while the right one is smooth. I _do_ wonder if they were manufactured in different ways as well.

On the other hand, Porsche can't be the only market for this knockoff fastener; just one of many revenue sources for the manufacturer.

Porsche has minimum specs for their vendor materials. This bolt looks like it was sourced for price and size only; fairly easy for a parts house to do if they felt it was OEM spec, could pass it off as "to spec" or unwittingly didn't know/care. If it was a knockoff, it'd have the requisite markings on the head. I wonder how many parts managers know about fastener specs or how many counter clerks inspect the fasteners that fill the parts bins?

If in doubt, buy directly from a reputable fastener supplier or parts house.

Sherwood

Someone once told me, Porsche doesn't make anything, they are just an assembler. With manufacturing cost being lowest in China right now, I wouldn't be surprised if some of the subs were having parts manufactured there. It's not that China can't make quality parts, you just have to pay a little more for it to be made high quality.

Your points are very good, Sherwood, but I think he actually did buy from a Porsche Center (Dealer), and he said they were originalteile. Unless the Dealer is up to no good (why would they be on bolts), it sounds like a porsche quality problem. As you said, either the bolts were only bought (by porsche) on size and price, or perhaps the supplier lied about the bolts conforming to a porsche spec.

As for cast vs forged, I think a better description would be cast vs. wrought. Bolts are made of wrought bar stock that is hot rolled to produce the desired shape. So while they are not technically forged there has been some hot work performed on then. Also wrought materials are much cleaner, usually with a precise composition and very little non-metallic inclusions. Before additional work is done the material would be heat treated to the desired strength. Very high grade fasteners, like flywheel bolts I would assume, then have the threads rolled and the end forged to mushroom out the material for the head. Then the head is drilled and machined with a specially fixtured 5 sided cutter for a six point socket or the shape is EDM'd into the head.

In the US all SAE graded and most ASTM graded bolts must also have the manufacture's mark on the head. Even though it is required to use the markings there are many bolts around without them. Just last year I made our shop supplier take back hundreds of bolts that were not marked. I'm not sure if ISO has the same requirements, anyone know?

Bolts and screws (except for very large ones) are not made this way. If they were, we wouldn't be able to afford them. Usually fasteners (even the high strength ones) are cold headed from wire or bar stock (which had it's origin as a cast ingot that was rolled and drawn down); then threads are rolled and last of all heat treatment and plating or coating is done. Most of the work is done automatically on machines which produce the fasteners at rates of hundreds or thousands per hour. Cheers, Jim

Jim, you're correct my experience is more with large fasteners costing from hundreds to thousands of dollars each so I'll accede to your description. But, if you do more than just a stress relief after thread rolling I think you would lose most of the benefits of the rolling.

Stress relief is just one type of heat treatment; high strength fasteners undergo a heat treament schedule that strengthens and toughens the material. 12.9 class screws are made from quenched and tempered alloy steel; they are heated to above the transformation temperature (temperature depends on exact alloy composition), quenched in oil (produces the martensite which gives the fastener it's strength) and then tempered by reheating to at least 380 degrees C. Tempering forms fine iron carbide crystals; this softens the material slightly but significantly improves the ductility (toughness). Cheers, Jim

I would be more than happy to hardness check that failed bolt vs. a known 'genuine' article..

Of coarse it would be nice to know the design spec. to compare it to..

Chris

For a class 12.9 screw HV specification range is 380 to 430. However, I suspect the failure cause will be determined to be incorrect form: too little cross-section at the transition from head to shank. Jim

I bought them from an oficial porsche centre at $15 a piece, they came in a sealed plastic bag with porsche partno, barcode etc. The bag also had the usual marking "Kontrolierte Qualitat" :rolleyes:

Andreas wha apparantly suffered from the same problem bought them from Mittelmotor. I know that these guys also order direct from porsche for most parts.

If someone would like to test one, I have five left and putting one in an envelope would be no problem.

I think at $15 a piece you'd be better putting them ALL in an evelope and sending them back to Porsche for a refund!

Sorry, I can't seem to leave this alone :) I don't have the SAE, ISO or other standards to quote from but all the reference material I have says that threads are to be rolled after heat treating. If a bolt is taken to it's transformation temperature after thread rolling it would lose most of the benefits of rolling.

SOMETIMES NEW PARTS DON'T WORK

This sign should be on the wall of every shop. We encounter poor quality parts all the time, so chalk this up to " I'm glad it failed before I installed it."
These kinds of failures are why warranties exist.