Ted I'm almost at 2 years on my 2.4 motor daily driven. When would you recommend putting new bearings in?

 

No one can fault you for that idea if you have a good several thousand km on it and if it has seen hard use, especially with that long stroke crank.

Changing the rod bearings is relatively inexpensive and easy as compared to changing rods, or worse, changing an engine. If the bearings prove to be worn, you'll be glad you changed them. If they don't, you'll have peace of mind and some indication as to how long you can go before feeling the need to recheck and replace.

 

Thanks for the reply. Would you recommend changing the rod bolts as well? I had to replace bearings when my oil pump began to dig into the front cover after only 2 weeks into running the motor. I swapped main and rod bearings then even though they looked ok just in case the front cover material got anywhere. I use a rod bolt stretch guage to fasten the rod bolts and moly lube.

Reason I mention this is because the rod bolts have been fastened down twice now.

 

I always change rod bolts once they've been run and loosened, and suggest the same. I recommend something better than the base bolts, like ARP Custom Age 625.

 

If in fact it was rod failure that Al suffered and not something else catastrophic when making 1062whp, the retorqued Groden have exhibited a tendency to weaken the thread area of the rod bolt. We have one customer that had rod bolts strip out on two seperate rods on the second install to proper torque per Grodens spec. Sometimes its just a reuse issue, not necessarily material.

With that said, we had Paul's motor apart 3 times last season and retorqued the Grodens without any issues. That motor saw 900whp to 1100whp with the same rods being reused with ZERO failure. We did replace them at the last service interval on the motor for piece of mind (and prior to Al's issues) as they had over 100 passes on them. The BME/R&R design is superior in my mind and uses L19 or 625 rod bolts. You can order them with 8740 but for the price difference of $65.00 why would you?

What is a suitable metallurgy test to see if the 15k street and strip miles on Lucas' rods has in fact weakened them? Shear test from a new rod to an old rod? The max stretch spec is .008 and I dont think there would be a spec if it didnt happen. The fact that these have yet to stretch is an indication to me that they are fine. For me it will be at least 15k before I have a set of Rods personally that I can have any tests done to. I will see if I can get some data from Mike after the holiday for service interval and tests that I am sure they have performed over the years.

Can you have these sonic tested or X-rayed or anything non destructive? I am not sure of what metallurgy you can do as its a field I havent spent much time looking into.

 

I believe your assessment is correct . . . so far. Apparently, once stretched, Al cannot return to form. The real question is how much time or stress will the rod take from the time it stretches until it fails, and is there anything internally apparent that would signal stretch is imminent.

I'd like to see Lucas go another 15k miles and see how they hold up. Even 15k miles of regular use is far more meaningful to me than 100 passes at the dragstrip.

 

TedB, you are correct, aluminum, once it stretches, it does not return to original form, hence a non-elastic material. Steel will, as long as it is not taken past the yield point. Funny, but this is a main reason why Evos are expensive to fix, once you dent an aluminum body panel, the only way to get it out is to replace it. (obviously depending on the physical size of the dent).

 

A good note I seen in the aricle.... On the street, old myths about aluminum rods are slow to die. Some say aluminum rods won’t last and must be replaced after 15,000 to 20,000 miles if they are used on the street. However, makers of aluminum rods say a set of high grade forged aluminum rods can last upwards of 100,000 miles in a street application. It all gets back to cost and weight. If a customer wants throttle response, or has a high revving engine, light rods of either aluminum or steel would be a good choice. But for a high torque, high load motor with a limited rpm range, steel rods would probably be better.

 

Jeff, I noticed that too. One other thing I forgot to add is that sprintcar motors have used aluminum rods for years and they'll go a whole season of HIGH rpm on a 410cid small block on the same rods.

 

I am not sure if he will post in here or not, but after talking to Mike at R&R today (the maker of our rods), stretch is not an issue. They will expand when hot and contract when cold but they do not stay stretched. His words are if it goes in at 6" and you have a rod that is 6.020" cold you need to buy new measuring equipment. Really a top class operation.

That being said we are now an OFFICIAL dealer as well.

 

Apparently we are talking about two independent issues as one and the same, but they are distinctly different.

Seeing actual, measurable stretch would indicate permanent, irreversible damage. This is not normal, and would quickly destroy the rod.

Heat cycling and heat expansion are normal and unavoidable, and it is this which is the source of long-term fatigue that eventually causes the structural failure of aluminum. Heat-related expansion is also why aluminum rod engine building always calls for additional piston to head/valve clearance.

Another thing this tells us is that checking for stretch is not useful as a means of predicting imminent failure. I'm not sure that can be done short of removing the rods, but if that is the case, it wouldn't make sense to remove and not replace.

 

I agree Ted. I am talking about 2 things and wasnt very clear. Heat cycling is still a very real issue and whether we get 5,000 or 50,000 miles out of the rods it still only has X amount of cycles. If somehow a rod is permanent stretched it is done, however Mike didnt think that was likely to stretch.

The main issue is more likely to be damage to the big end because of detonation or excessive cylinder pressure than rod stretch anyway. Even then, Rau is running 90psi on a high compression methanol motor without rod failure after trying a few other manufacturers.

cliffs- Ted said what I should have said

 

Google NDI or NDT. One Method that fits what you need done without destroying the rod would be Ultrasonic Pulse Echo Technique

But in the aviation field we do it all the time on all kinds of materials. Honeywell does the Hot sections of our turbines. But its tests the Blades to make sure they can survive another 2000/4000 flight hours without failure.

http://books.google.com/books?id=0MS...sult#PPA465,M1

for you info junkies

Oh yah:

NDI = Nondestructive Inspection

NDT = Nondestructive Testing

 

There are cyclical fatigue charts available for many aluminum alloys (particularly aerospace alloys) that can give a good idea of how long you could expect these rods to last. The heat cycleing adds a whole other element to it, but it would at least give you an idea of what to expect.

Aluminum doesn't have a fatigue limit. Weither its 1 million cycles or 10 million cycles, aluminum WILL fail eventually even if it was never overloaded. This isn't something cooked up by old school domestic guys, it's got thousands of charts and tests behind it.

The statement of 100 passes being harder on aluminum rods then 15,000 miles of street use is not necessarily correct. It all depends on the alloy and the loads seen. Some alloys cannot handle huge loads (2024 aluminum for example), but will resist cracking for MANY more cycles, where other alloys can handle huge loads but do not like to be cycled nearly as much (most 7000 series aluminum).

Hell, some aluminum will crack just sitting on a shelf from residual stresses left from machining (7075).

 

Another thing i would worry about also in a all Aluminum rod would be the threads. First time torqued is fine..but what after reuse. In some Rotax engines i have worked on in the past we used a Time Sert (http://www.timesert.com/) on areas that were repeatedly re-torqued on aluminum heads. The timesert would last alot longer and less prone to Double-Threading/Stripping then just the bare Aluminum.