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Rod strength

General engine tech -- Drag Racing to Circle Track

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turbo camino
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Re: Rod strength

Post by turbo camino » Mon Dec 02, 2019 7:51 pm

These are either early production or development PM rods for the Cadillac Northstar, sorry I don't remember which, it was 30 years ago... One pulled off the line just after the initial cold pressing, other pulled after the last hot forging.

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Re: Rod strength

Post by ptuomov » Mon Dec 02, 2019 8:20 pm

Is the problem (or the perceived problem) of fragility about powder metal vs. conventional forging? Or is it about designing the material to make the end cap crackable? There are conventionally forged cracked rods, but they also have to be heat treated etc. to be crackable.

I have ancient non-cracked powder metal "PPF" rods and you could use them as a hammer, I don't think they would crack.

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Re: Rod strength

Post by modok » Mon Dec 02, 2019 11:11 pm

people just find it very strange.
I did too when I first encountered the stuff, but that was 25 years ago.
Once you get used to it.....it's pretty cool stuff.
$ for $ better than forged mild steel,
and.....Whenever joe blow is talking about rods, it's always the subject anyway. About how he can get NEW ones from summit and it's better deal than...whatever. If they want most bang for the buck as priority #1, this is what they SHOULD want.
Because of the process being so well controlled, each one comes out identical and nearly perfectly balanced.
One "downside" is the material is only 90% as dense as true steel, but, is that even a problem? Not really. If anything that's an advantage when under compression. I doubt the figure of 1500lb is correct, tho.
Either that's prior to some mechanical advantage of the machine, and/or they are partly bending them to crack them, in which case there should be torque component.

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Re: Rod strength

Post by dannobee » Tue Dec 03, 2019 12:59 am

Back when I was working at a Chevy dealership and racing circle track late models, we'd build "claimer" engines for the lower division guys. When the PM rods came out and ample core engines were available, we figured what better place to check their durability. I never saw one fail. Period. Never ran them in the upper division cars, but they worked great for claimers.

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Re: Rod strength

Post by midnightbluS10 » Tue Dec 03, 2019 7:00 am

mag2555 wrote:
Mon Dec 02, 2019 6:50 am
If it only takes 1500 psi to crack these Rods in there thickest section, then how strong can these production Rods be?
Its a 'pre-scored line'. They didn't just crack a solid chunk of metal, with 1500 psi in a targeted manner. There was already a failure point built into the rod so it would crack there. I also doubt they just cranked up the pressure and it cracked. They likely used some sort of force connected to that 1500 psi, one would think.

That's a whole lot different that sticking a rod into a pressure chamber with 1500 psi and having it crack somewhere.

You can't make any determination of how strong a rod is from that.
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Re: Rod strength

Post by mag2555 » Tue Dec 03, 2019 7:43 am

I fully understand the procedure used to split it even before I posted this, I was just very surprised that cracking at the same time 2 of the most meaty sections of the rod took only 1500 lbs of applied force!

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Re: Rod strength

Post by ptuomov » Tue Dec 03, 2019 8:47 am

mag2555 wrote:
Tue Dec 03, 2019 7:43 am
I fully understand the procedure used to split it even before I posted this, I was just very surprised that cracking at the same time 2 of the most meaty sections of the rod took only 1500 lbs of applied force!
Here's a question: Do they press it with 1500 lbf force or do they have a rig that drops a 1500 lbs weight on it from some height? I vaguely remember that when one of the Japanese motorcycle manufacturers developed a conventionally forged crackable rod. I think they were dropping the weight on the rod to crack it.

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Re: Rod strength

Post by midnightbluS10 » Tue Dec 03, 2019 10:46 am

mag2555 wrote:
Tue Dec 03, 2019 7:43 am
I fully understand the procedure used to split it even before I posted this, I was just very surprised that cracking at the same time 2 of the most meaty sections of the rod took only 1500 lbs of applied force!
Sorry! :oops: For me, that wasn't clear in the original post.
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Re: Rod strength

Post by lefty o » Tue Dec 03, 2019 11:10 am

in my experience, and i may be wrong, but in general powdered metal, or MIM etc, are all very strong in the direction they were designed to take force, but when force is applied in a different direction the stuff is fairly brittle.

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Re: Rod strength

Post by ptuomov » Tue Dec 03, 2019 12:30 pm

We’re working on these super light, non fragile new custom con rods. Bearings that fit these may be a little short:
A8A345B0-10CC-4443-B77A-9F6220C5B2DA.jpeg
The pistons should not score alusil, nikasil, or cast iron! Pin weighs more than piston and rod combined...

;)
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Re: Rod strength

Post by turbo camino » Tue Dec 03, 2019 12:40 pm

If force is applied to a conrod in a direction other than what it's designed for something else has already gone horribly wrong.

The PM rods seem to bend/buckle when overloaded, not shatter. I don't know that I have ever seen one broken that wasn't killed as a result of some other component failure. I have seen a lot of them bent and twisted up like pretzels, as in my picture at the bottom of page 1.
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Re: Rod strength

Post by exhaustgases » Tue Dec 03, 2019 5:36 pm

turbo camino wrote:
Tue Dec 03, 2019 12:40 pm
If force is applied to a conrod in a direction other than what it's designed for something else has already gone horribly wrong.

The PM rods seem to bend/buckle when overloaded, not shatter. I don't know that I have ever seen one broken that wasn't killed as a result of some other component failure. I have seen a lot of them bent and twisted up like pretzels, as in my picture at the bottom of page 1.
And like the video, just don't have a nick or score mark on one, like the fellow that showed the huge gouge on the big end.

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Re: Rod strength

Post by bobalattie » Thu Dec 05, 2019 1:57 pm

5.2 mustang gt350 voodoo engine. Had bearing failure then the bolt let go..
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Re: Rod strength

Post by digger » Thu Dec 05, 2019 3:30 pm

lefty o wrote:
Tue Dec 03, 2019 11:10 am
in my experience, and i may be wrong, but in general powdered metal, or MIM etc, are all very strong in the direction they were designed to take force, but when force is applied in a different direction the stuff is fairly brittle.
The cap gets cracked off on the direction the rod is loaded in the engine

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Re: Rod strength

Post by lefty o » Thu Dec 05, 2019 4:07 pm

digger wrote:
Thu Dec 05, 2019 3:30 pm
lefty o wrote:
Tue Dec 03, 2019 11:10 am
in my experience, and i may be wrong, but in general powdered metal, or MIM etc, are all very strong in the direction they were designed to take force, but when force is applied in a different direction the stuff is fairly brittle.
The cap gets cracked off on the direction the rod is loaded in the engine
after a stress riser is put in them.

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