you ever look at the underside of a nice piston?? they tend to have full internal machining, and they do nothing to remove marks, it doesnt mean that the part is cheap. i build aerospace parts for my full time machining job, they have tool marks.... doesnt mean that there bad.

 

Bah. Never said they were bad, forget it.

 

pistons aren't loaded the same way a connecting rod is.

 

It may sound like a joke, but a 50 dollar or more Novarossi rod has less imperfections than those rods. They may say the machining marks do not make a difference, all I know, at least on R/C, I have never seen a rod with such terrible imperfection.



The above set costs $260.00, piston and sleeve, LOL, and is the size of a half dollar.



Isn't this a work of art?

Attention to detail is key!

 

Its so cute! Its like an expensive key chain.

 

I actually use one of those for a keychain.

 

I have one to from one of the R/C buggy engines seized up using 45% helicopter nitro fuel.

neogenesis, nice! LOL

I am so glad I found this thread, posted the pictures on another website and people were like WTF, its crazy all the info one can get from the web. I will definitely pass on these aluminum rods.

 

My snowblower's old engine was a Tecumseh, it blew up when the governor spring broke.

On dissasembly it had an iron crank, steel valves, wrist pin and rings and aluminum everything else. The aluminum rod went right through the block as well as any steel rod.

 

Fatigue is the biggest problem I see with Aluminum connecting rods, and the reason why they are only really appropriate for short term racing use as far as I'm concerned.

Aluminum and Steel have very different fatigue properties, here are a couple S-N curves for some random steels/aluminums Link Link

Depending on the exact materials there will be some variation, but in general the fatigue life of steel is much better. The biggest problem I see with aluminum is that is has no endurance limit. With steel, as long as you keep the stress below the endurance limit the part will have infinite life. There is no endurance limit for aluminum, its S-N curve will never level off like steel, and it will never have infinite life. Given a connecting rod sees 10^6 cycles in only 4 hours at 4000rmp, fatigue life seems rather important.

With the size and weight constraints put on aluminum connecting rods, the stress will be quite high and the number of cycles to failure won't be all that high. This is why aluminum rods need to be checked for stretch and crack propogation. A steel rod can last essentially forever, but an aluminum one never will. As long as the engine is running, the rod is getting a bit closer to breaking, and you have to keep and eye on it so you can try and change it before it destroys the rest of your motor.

 

That is a very interesting link, and your post does make sense. However, will a street motor approach the stress level that will eventually break a rod during that motors normal life span? If the rod is beefy enough could it possibly last longer than other internal wear items in a motor? That is the sixty four thousand dollar question.

 

street motors break steel rods.

by the way, is anyone running these yet?

oh.

I didn't think so.

 

10^9 cycles is nearing infinite life for a connecting rod. It's about 250,000 miles at 60 miles/hour (4000 rpm estimate). It might be possible to design a rod that ideally would have low enough stress to be in this range, but cracks would still be a problem. If there is even the slightest imperfection in the material or the rod gets nicked or anything isn't perfect, there will be a crack, the stress at that crack will be high, and it will propagate to destruction in a matter of hours.

Anyone know of any applications that use aluminum rods, and what their inspection/replacement schedule is?

 

like
oh
i dunno

machining marks?

 

I used to work at a mustang shop and we built a turbo small block 05 mustang gt race car. We started with a nascar engine that was a never used back up for one of the dale jr teams trucks. The engine had je pistons and titanium rods. The rods were the first failure and the exhaust valves which were coincidentally titanium as well were the second failure. 2 of the rods bent at 1300rwhp which is nothing compared to what other engines in the same class were making on aluminum rods. Some of the cars in that class were making 1500hp with turbo small blocks.

 

The highest quality aluminum rods like BME's will not have machine marks. They are literally pounded into shape by very high preasure, than polished perfectly smooth. It is a forging process that makes them appropriate for use as a connecting rod, unlike billets that are cut into shape. The aluminum rod pictured was obviously cut from a billet block.

 

Again, I question the quality of the process in making those titanium rods. Were they from a reputable manufacturer? Also, he may have encountered a horrendous tuning mistake. We all know what happens then.

 

IE low rpm, 3600 in my case, constant speed low power motors. The width of the rod was about the same as a bp rod but on an 8hp motor. Can't comment on lifespan though.

 

AL rods are used in uber high hp stroked out drag motors. Replaced after each run along with the rest of the motor.

 

That is not true. I talked to a Top Fuel mechanic and he said that the rods will last several events (maybe a whole season, I can not recall exactly what he said), unless they are damaged from a blown motor. The motor is taken apart after each pass where gaskets, rings, bearings, and fluids are replaced. Crank, rods, and pistons are reused.

 

Well, since you said it, and its on the internet....IT MUST BE TRUE!