aluminum rods?

P Clingman · 03-24-2008, 03:22 PM

Hi all, My Friends 930 engine vomited (rod out the side) he swears the rod is aluminum I don't believe it has anybody seen an aluminum 911 rod? in a street engine. Palmer

Steve@Rennsport · 03-24-2008, 04:39 PM

Thankfully, I've never seen anyone use aluminum rods in these engines,...

I'm pretty sure that there is no room for such things inside these engine cases.

Aurel · Aurel's Garage

Maybe it was titanium. Ti looks a bit like Al...

Aurel

rcwaldo · 03-24-2008, 08:08 PM

I have used ally rods in small block chebies -- and boy are they noisy in the morning

I have never seen one used in a 911 engine. And like Steve says, thankfully so

P Clingman · 03-25-2008, 02:01 PM

I am going go look at the engine tonight I will report back my findings Palmer

P Clingman · 03-25-2008, 04:10 PM

I just saw the engine the rods are definitly aluminum. the heads are not off yet so I could only see a stub of a broken rod poking thru the case, The crappy thing about this is the
prevous owner had taken this stock 930 with 140k miles to a well known Porsche
shop south of boston for valve guides and a top end reseal and now 20k miles
this is what he got a 930 bottom end with a knifedged crank and allum rods
and now a window in the block?? my thoughts are he got screwed now he needs a case
rods and one piston and cylinder or another engine. Palmer

YTNUKLR · YTNUKLR's Garage

I ended up with a set in trade of 5 aluminum rods of unidentifiable manufacture. You can guess why I only got 5. 5 desk paperweights is plenty.

cfc · 03-25-2008, 06:59 PM

There has been alunimum rods for sale for 911 engines for 20 years at least.

Eagledriver · 03-25-2008, 09:05 PM

I'm not an expert on metals but I believe one property of aluminum is that it fatigues when it flexes. Steel and other metals have virtually no fatigue when flexed below bending. Aluminum fatigues no matter how little it flexes. This is why aircraft have a finite lifespan. This characteristic makes aluminum unsuitable for applications like connecting rods.

-Andy

911pcars · 03-25-2008, 09:37 PM

All metals have a fatigue life. Aluminum happens to have a shorter life than other materials. Designers attempt to compensate for this shortcoming by designing the con rod with larger cross sections and beefier construction. In some race applications, less reciprocating weight is a higher priority than durability.

Sherwood

Mo_Gearhead · 06:06 AM

QUOTE: "This characteristic makes aluminum unsuitable for applications like connecting rods. "
_________________________

You must be joking?
If you do not know an answer to a technical subject ...please, do NOT just post your 'wild-azz' assumptions.

Bullet Bob · 03-26-2008, 12:09 PM

Steel components can be designed for infinite fatigue life based on the stress levels and cycling properties (fully reversed stress, etc...). If a steel part can sustain 1 million cycles without failure in its designed application it will generally last forever. Aluminum can't.

There is no benefit to using aluminum rods over steel because they are such highly stressed parts anyways. The strength to weight of aluminum and steel are the same so to meet the strength requirements with an aluminum rod it would end up weighing the same as a steel rod.

Titanium has a much better strength to weight ratio than aluminum or steel so you can meet the strength requirements and have a lighter part. Ti is very fatigue sensitive however, which is why they are usually reserved for race applications and replaced on given intervals.

kenikh · 03-26-2008, 02:29 PM

Quote:

Originally Posted by Bullet Bob

Steel components can be designed for infinite fatigue life based on the stress levels and cycling properties (fully reversed stress, etc...). If a steel part can sustain 1 million cycles without failure in its designed application it will generally last forever. Aluminum can't.

There is no benefit to using aluminum rods over steel because they are such highly stressed parts anyways. The strength to weight of aluminum and steel are the same so to meet the strength requirements with an aluminum rod it would end up weighing the same as a steel rod.

Titanium has a much better strength to weight ratio than aluminum or steel so you can meet the strength requirements and have a lighter part. Ti is very fatigue sensitive however, which is why they are usually reserved for race applications and replaced on given intervals.

Except in cars like the Honda S2000 and GT3; they are supposed to have an undefined service life. I am not arguing the fact that Ti fatigues...it does. But over-engineering can take fatigue out of the equation by building the rod beyond an expected service life.

jmz · jmz's Garage

someone around here did it years ago. ran good with the lightweight rods right until it didn't run anymore...

Eagledriver · 03-26-2008, 03:46 PM

Quote:

Originally Posted by Mo_Gearhead

QUOTE: "This characteristic makes aluminum unsuitable for applications like connecting rods. "
_________________________

You must be joking?
If you do not know an answer to a technical subject ...please, do NOT just post your 'wild-azz' assumptions.

Actually that quote came from Bruce Anderson's 911 performance handbook. It is not just a guess but an opinion. Just because you don't like my answer doesn't make it a joke.

-Andy

YTNUKLR · YTNUKLR's Garage

Coatings allow Ti service life to be much extended. The issue with Ti is not so much a direct result of fatigue, as galling. Galling is when the surface of the metal is compromised, and it leads to surface risers and eventually cracks. To stop galling Ti, they have surface coatings to minimize the potential for surface risers to even develop-

Mo_Gearhead · 03-26-2008, 04:17 PM

QUOTE: "Actually that quote came from Bruce Anderson's 911 performance handbook. It is not just a guess but an opinion."
____________________

Opinion ? Whose? His or yours?

With all due respect to you and Mr. Anderson. There are LOTS of engines that have been built/raced with aluminum connecting rods. I (and my friends) have built some myself. To say that "aluminum is unsuitable for use in connecting rods" is an ignorant statement. Thus my comment. Some people come to these boards to learn something.

Perhaps the misunderstanding on my part was that your generic statement seemed to apply to "all engines"...when (in your or Mr Anderson's mind) you/he meant "Porsche engines"???

930gt-40r · 930gt-40r's Garage

The top fuelers use aluminum rods to ubsorb the impact of combustion, but they only get used once. I guess on the street where the have to see accel/decell they may get "stretched" faster?

jmz · jmz's Garage

someone around here did it years ago. ran good with the lightweight rods right until it didn't run anymore...

cnavarro · 03-27-2008, 05:52 AM

Yes, aluminum rods have been done before for a 911 (CMW sold them years ago) and even for aircooled VWs, even in a configuration of an aluminum rod with a steel cap (yikes!). The guys I work with on the billet steel rods have been making aluminum rods for decades, but have never chosen to do any for Porsche because in their opinion, it's not needed and too much of a liability. In some applications, a steel rod is too rigid and will snap the crank. They use an aluminum rod as a shock absorber, and treat it like a service item. Some engines get new rods every few passes, some every few hundred passes. Some have even run them on the street, but they recommend against that. Aluminum rods are disposible parts and must be replaced often, since a failure is pretty catastrophic! Ti is the way to go if you need light rods for a Porsche, as the factory did :-)

If you feel like learning more about aluminum rods, check R&R Racing Products out - http://www.rrconnectingrods.com

I won't claim to know everything about their rods, but I have been around them long enough by osmosis I have learned quite a bit about both aluminum and steel rods :-)