can i run aluminum rods on the street????

If I rememeber right aluminum rods have a cycle life rating were steel does not. What I'm trying to say is over long time aluminum rods will weaken a certain percent. Fail...maybe but they will not take the abuse they once did. If you take it easy on the street yeah they will last awhile.

 

The new aluminum rods are fine for street use, I run them in my blown Hemi. Just dont run your motor hard till its warmed up. The old aluminum rods from the 60's and 70's are a no no.

 

i think that about covers it right there.when i run mine it was the late 70s and they were brand new.i was told by a guy a rhs that it would be the way togo.he also told me all the ways a could destroy it.i know i was very lucky.i dont know what i would do today.but with better material and manufacturing i might do the same today.

 

Cyclical fatigue:
http://en.wikipedia.org/wiki/Fatigue_(material)

Bob

 

Once used, the only thing they're good for is paper weight!...

 

When you say "fine", to make that information useful to others contemplating the use of aluminum rods on the street you should clarify what sort of use is fine. Per what was discussed earlier, a hobby car vs ten of thousands of miles, cross country trips to Wally World, etc.

 

I think when it comes to aluminum rods we can see from the past 4 pages, there is no ONE correct answer. As said many times, its all about fatigue. They work great in compression, lousy in tension. Big,heavy pistons create more stress on the rod during the intake stroke, causing more fatigue, which leads to failure.
One reason the BSAs(which initailly ran Al rods and cap) and Trumps(al rod with steel cap) worked is the type of alloy AND the fact that for the rod size, the pistons were small.
We have run both Al and steel rods in our Bonneville cars as lots do out there. Al rods in a land speed car is very common, but as well a bit of a unknown area. THis also has to do with there arent near as many guys building lsr engines than drag motors. You can get away with alot for a 1/4 mile, 5 miles is different. We've had great success with Al rods in some motors, but when the HP starts to get up there we prefer steel. We had a 540 BBC that the motor builder wanted to use Al rods due to the weight..we did... and it lasted 3 passes before it gernaded...as in the starter was in the NOSE of the car...this year we had a 296ci sbc turning 9000rpm and 1500 or so HP...we used steel rods.
There is lots of data from years of racing 1/4 mile for cr maintenence, when to swap them etc etc...not so much for lsr....even less for street cars. There are just too many variables, its a crap shoot at best. what is worse usually there is no notice like a rod bearing knocking...they like to let loose when it can do the most possible damage...

and we won't even get into the theory that Al rods last longer in a blown motor due to the boost pushing down on the piston on the intake stroke, thereby lessening the stretch...

Feel free to see my post from yesterday if you want to see a in-car video of the screaming sbc mentioned above.
Hans

 

Yes, the pistons were light, the engines had a short stroke, they didn't rev real high, and old bikes weren't generally ridden the number of miles that are done today. Beyond that, they couldn't go too long between overhaul, so the engine was torn down and reconditioned more often than engines usually are.

A lot of lawn mower engines have aluminum rods so they must be ok.

 

Al, Triumph 650's have a 3.25 inch stroke,same as a 327 Chevy, and will rev to 7000 stock.And make just over one HP per cubic inch stock . Back when I drag raced them ,near 8000 was what a modified engine might see.Nitro fueled Triumphs were good to about 80 HP on stock rods.Triumph endurance racers could take 7000 plus rpm for an hours or so at a time.The rods are beefy and pistons are very light compared to car engine stuff.Broken rods were rare .
Yes on the short overhaul life.....And today guys still beat the shit out ofTriumph engines on 50 year old aluminum connecting rods

 

Just remember this, when it does blow up....even if it is 10 years later, we'll say...."I told you you couldn't run aluminum rods on the street"..........it's just our nature....hehehe

 

Has anyone heard that Bill Miller is now out of business after paying off all of the law suits because his rods failed on the street? I love this place, the drama the top.

Frank

 

So now, the truth comes out... Sad!

 

I wouldn't do it. I ran a set in a 7500 rpm small block Chevy drag race application. I was told to replace them at 200 runs but I new better. At run 241 it cost me a short block and 1 head. It just broke right above the rod journal. Bottom of the rod was still on the crank and the bearing looked great.

I read all the posts about motorcycle and jap car engines using them. Well, so do lawn mower engines. Check out Manley Sportsmen rods. Decent price and you wont regret it.

As for used rods, they are just as useful as used valve springs. You can build cool trophys and garage art with them.

 

Correct.

Aluminum fatigues with cycles, most steel and Titanium alloys do not. This is why racers replace Alum rods regularly and airplanes get re-skinned and retired regularly. Most aluminum also loss strength over time due to "over aging" where the heat treating is degraded by the heats that engines do or can operate at, again most steels and TI alloys do not have this problem.....which is why most rods are either steel or Ti.

Alum rods WILL fail, the only question is when. Running Alum rods on the street is just a bad idea IMO.

 

More than I remembered, but 3.25 isn't a lot of stroke. Those engines were far from being indestructible. With stock parts the limit was 65 HP and a short life. At 80 HP the crankcase was on the edge, and to do that with any reliability better parts were needed.

If your point is that aluminum rods are great and last forever, why are they only used in certain specific applications? Is everyone clueless, or do aluminum rods only make sense for certain uses? While a good aluminum rod would cost more than the cast or powdered metal rods most car engines have, there are high end vehicles where the extra cost wouldn't be an issue. In spite of that, no one does it. The GM LS76 engine is a big dollar street engine. It even has dry sump oiling. But where any rod was a possibility they went with titanium(a material with good fatigue properties), not aluminum. I could go on, but you understand my point.

 

Steel and titanium do fatigue. If that wasn't so the only parts that ever failed would be ones which were overloaded. However, below a certain threshold of stress, yes, they will theoretically last forever. The fatigue life of aluminum is less predictable than steel; crack propagation and total failure are also less predictable; and aluminum is more sensitive to stress risers, imperfections, notches, etc. Beyond that it is more flexible for a given strength, it expands and contracts a lot more with heat, and it can't tolerate heat as well. Aside from all those things it's a good material for connecting rods.

 

That's a dead link...

 

Sorry.

 

Fuck it, I'm going to start using Steel rods with aluminum rod bolts! THis way I CAN predict failure! I think we are starting to argue for the sake of arguing here guys. But to the OPs original question, anybody that would recommend him to use Al rods in his application is a fool. No I havent had my coffee yet.

 

How about some donuts or bagels with everything and cream cheese.... Yum!...

 

My point is not aluminum rods are great,they aren't on a street car engine.It's a reply to you saying Triumphs were short stroke low rpm engines.
I raced Triumphs and I know their limitations.In fact I still build them.

 

I ran aluminum rods on the street (392 hemi). Always had problems. Short (and I mean short) trips, all good, but once the rods heat up, they grow!! It throws timing off and my pistons were actually getting pushed into the head. Created lots of heat and scorched the exhaust valves - next, piston helps close the valve and yep, valve gets bent. Start all over. These are not cheap to build! I now have K-1 rods and are working out great.

 

I'm guessing this is not what you want to hear 'cause you already have them. Opinions I have read from what I consider experts are that you can run them, but why? They have a finite life. I've heard 100 runs at the drag strip. I've heard 500 laps in roundy rounds. When they go, they take most the whole motor out. You don't know whether a used rod has 1 run or 100 runs on it. I know a guy that ran aluminum rods in a 327 in the 60' and 70's. Shifted at 9K, thru the traps at over that. He did all his own work. He knew how many runs he could get and how many he had on each rod. He knew how much they could stretch, etc. I don't think he got much over 100 runs out of them.

I personally would not take the chance.

My 2 cents,
Dan

 

http://www.dragzine.com/tech-stories/engine/debunking-aluminum-rod-myths-with-grp/
http://www.dragzine.com/tech-stories...yths-with-grp/