Carl Fausett

There you go - that's good information, Roger.

GregBBRD

Kudos to you for researching the materials so throughly. Most people who look at a new part don't take into consideration the costs involved in creating that part.

When I was originally thinking about this piece, I've always wondered if it was actually cast, or if it was sintered, like the connecting rods. Sintered metal, since it is highly compresseD and resistant to more compression, would be a desirable feature in an application, like this. And these fractured parts have always looked surprisingly similar to a fractured sintered connecting rod. Would your material testing be able to differentiate between the two?

The change in material between Porsche's old and new piece is very difficult to figure out. They went to the extra cost of casting/sintering the original and then machining that part to simply machining out a part from relatively soft steel?

With that information, I would agree that your new version is much better than the current production piece....dramatically better.

Sounds probable that the original designers might have known more that the current bean counting parts procurement guys might know? After all, new S4 pistons from Porsche, don't have the oil return holes drilled!

I think you have a perfect opportunity to study your new part and see if there is anything new to be learned about compression/fretting, since you've been running it in your own engine through the current dyno testing and running.

Do you have any plans on removing and inspecting these pieces before Bonneville?

Bigfoot928

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Carl Fausett

No. I'd like to, but time will not allow it. My wife has now entered hospice, and her comfort is top priority for me. After that, I have all my regular work, plus prep of the race car after hours and weekend. Add to this that people are asking me to bring the race car to Atlanta for the Porsche event in June, and I am fully booked. The new intake manifold and several other parts will be further delayed as a result.

So - although I'd like to pull them prior to Bonneville for an inspection, it isn't going to happen. The material choice is sound, the design is good and the machining is first-rate. I'm going to have to trust it. It has already survived several dyno days over 1000 HP, and we've checked cam timing and there has been no movement, so we think we can check off on this part for now.

Carl Fausett

Looking at the grain structure of the broken part, it looked granular with no martensite showing, suggesting to me that it was cast and let to cool without quenching. If it were sintered metal, the pattern would be much more uniform.

It sounds like Adk46 has a background in metallurgy, and would be able to expand on that.

GregBBRD

I thought maybe the company that analysed the material, for you, would know this.

Somewhat of a moot point, since you've made something that has to much stronger than Porsche's replacement part.

Added Content: I took some time, this evening, and looked back at my notes about his part. The reason I suspected it might be sintered was the fact that there is a complete lack of tool marks on the outer perimeter of the original part....and there are no "parting lines" on the perimeter. A sintered part would come out from the initial molding and sintering process, looking exactly like this part. Additionally, this part almost entirely relies on compression to keep it tight, and a sintered part would not "compress" like a billet part would. Back 10 years ago, when I was studying this part to see if making a "stronger' part was feasible, I came to the conclusion that the part was, indeed sintered.

Carl:
I've never needed to purchase a new part, from Porsche, so I have no idea what it looks like (and I have no desire to order one.) Does the new replacement Porsche part have tool marks around it, indicating it was made from steel?
If so, weighing the "new version" and the "old version" should confirm the sintering question....as you know, a sintered part is very dense and thus weighs considerably more.

GregBBRD

I can only imagine what you are going through. My sincere sympathies.

And going to Bonneville sounds like great idea, if not to just help you get past what you are dealing with.

And I agree. This part looks great.....and has to be very low on the list of your current concerns.

Adk46

Sorry about your situation, Carl. People who work in hospice are great heroes.

Metallurgy is a vast field that does not attract much popular interest until something breaks. Lot's of amateur photographers, musicians, mechanics and those sorts of things, but I've never met an amateur metallurgist. Boring, I guess. I'm impressed you mentioned martensite, Carl - cool. Martensite comes into play for high-carbon steels: the "40" in "4140" makes that a a high-carbon steel. Only those are given the quench (austenite >> martensite) and temper (>> less extreme structure) treatment. I don't believe cast or powder metallurgy steel parts are given this sort of heat treatment often.

The "41" in "4140" tells you that quenching will provide the martensite even if you can't cool a part very quickly - the term "air hardening" is used. This characteristic is called "hardenability" and it comes as an expense from the alloying additions. If you have a thin part, you can get by with less hardenability, e.g., 1040. Fully martensitic material will have a Rockwell C of something like 63 (depends on carbon content). The tempering temperature will drastically affect all properties - it is the **** you twist to get what you want, one of the things that makes steel an amazing (and complicated) material. But what do you want? Ah - that ain't easy to figure out - where on the curve of tensile/compressive strength versus toughness do you want to be? They trend in opposite directions.

Powder metallurgy (sintered powder) is rarely chosen for anything but low cost. I agree that the part in question looks like a P/M part. Those in snowy locales know that the property of snow changes over time - it sinters, a process driven by surface energy leading to consolidation. P/M gives a near-net-shape part with a nicely uniform structure (compared to a casting). But common to castings, the grain boundaries are "au naturel" where contaminants like to go, hurting ductility. Some porosity always remains, and you'll have to live with whatever crap finds its way into the starting powder - crap that floats to the top during casting or gets busted up during forging. But do you need ductility for this sort of part? This is like asking if you should always wear a helmet - shop handling is always a concern, for example. It would seem Porsche was largely correct in answering "no" for nominal use.

But again, a proper design can work for any process, though "work" is a matter of probability in the regime of brittle materials. I think a Q&T'ed piece of 4140 steel will be more like Porsche's typical over-engineering - that is, good.

V2Rocket

crack appears to be in-line with the keyway, perhaps one of the "corners".
my guess is the crack begins at the corner, makes its way to the edge and splits the ring.

ever cut a piece of welded tubing lengthwise and watch the metal "spring" open once the tension is released?
though not in tension, the rest of the now roughly "C" shaped piece of metal (cracked O) can flex under load/stress and the fatigue happens ~180 degrees away from the original crack point, a sort of hinge if you will.

many other cars use round PINS instead of woodruff keys and do not report any issues with their cam gears.
maybe you could make a "half round half square" key and round out the hole in the propeller...better yet, round out both the camshaft and the propeller and have a fully round pin slide in.

this would eliminate the "corner" which is a known starting point for cracks.

(subaru cam gear)