The connecting rod is the backbone of the engine. I think many people overlook the importance of the connecting rod, or don't fully understand the number of important tasks this one single component of the engine does. I believe the connecting rod takes more abuse than any other single component in the engine. It most definitely takes the most loads. Understanding the connecting rod, and its role in the engine is the first step to building a reliable engine. In our case, we learned the hard way just how true that statement is.
Imagine a piston traveling from the bottom of the bore to the top of the bore, then having to stop, change directions, and travel from the top of the bore to the bottom of the bore again. Now imagine your hand is the piston, your wrist the wrist pin and your elbow the big-end. Punch the air 20 times as fast as you can. Does it hurt? Now hold a 10lb weight in your hand and do it again. Does that hurt even more? Why? Would you say the extra weight has added more stress to your elbow and wrist?
The highest tensile stresses occur in a connecting rod just past Top Dead Center (TDC) as the crankshaft is starting to persuade the piston to change directions and accelerate back down the bore. The stresses are even higher during the exhaust stroke when there was no compressive resistance of the combustion gasses to help slow the piston down. This stress is where the material, manufacturing processes and geometric design of the rod come into play the most.
The stock rods are up to the job of handling a stock weight piston at the stock rev limit. However, when you increase the weight of the piston, or change the piston speed, rate of acceleration or rate of change in acceleration (Jerk), you have just surpassed the capacity of the stock connecting rod. For the TTS 444cc kits, with 30+ grams heavier piston assemblies, you can see why we would want a stronger rod. But also, for our 450 engines, with an increase in stroke (higher Jerk and faster piston speeds) you can see the need for a stronger rod is imperative.
In addition to a stronger rod, we were looking to make things lighter as well. Therefore, we decided that Titanium was going to be the material of choice. At the time of designing the first evolution of 450 engine, I didn't fully understand the importance or minute details of the rods, and left it to the hands of those who supposedly did. I also figured that anyone could make a rod...right? I wasn't quite that naive, but apparently close enough.
Based on several opinions from some people in the car racing scene, A company called "Design-It Prototype" run by Larry Childs out of Petaluma, CA seemed to have a reputation for knowing what they were doing with Ti rods. They built several sets for Audi car racers with great feedback from the few I spoke to. So, I figured these guys knew enough to build us a rod that would work. They designed rods to meet our specifications for the NC-30 and the GSX-R1000 (circa 2001~2003). Unfortunately, we had nothing but horrible results with Larry and Bryan of Design-It Prototype with the eventual failure of every rod they produced for us. This was after being nearly a year behind in production. About the only good thing that came from this experience was the more detailed understanding of a connecting rod and the amazing working relationship I built from this with Carrillo Industries (more on that later).
One of the critical components of using Ti as a connecting rod material is understanding its tendency to weld to itself, or other materials, below the melting temperature of the Ti. If you run Ti against another part, you must run a protective coating, like DLC, on that surface or you will gall the metal - even with an oil film in between. One of my key warning signs of the Design-It guys was, they didn't know this. I had to insist on the coatings with them. Even then, we had issues.
In the above photo, you can see the DLC coating on th right, and the scuffed coating on the left. In the photo to the left, you can see what happens to the Ti when it is run against steel with no coating. This is still with an oil film between the metals. However, it just isn't enough protection for the soft Ti. The application of the DLC, and the base material it is applied to, must be properly matched or you will get peeling, chipping or delamination of the DLC, losing your protective coating. These rods are now destroyed and only make great paper weights.
Another thing to consider about rods is oiling for the pistons. Honda went through great lengths to add oil jets to spray the underside of the pistons to keep them cool, and keep the wrist pins lubricated. You'll notice that the oil jets in the stock rods have a lot of material added around them so as not to compromise the strength of the rod in that area. Where the beam meets the big-end is where you can see some of the most stresses in a connecting rod.
Once the Design-It Prototype rods were done, we realized there was no allowance for oiling of th pistons. So, in an attempt to mimic the Honda, we drilled our own jets. This was done as an afterthought, and really compromised the integrity of the rod at that point. Since we didn't know it at that time, we ran with them like that.
Later in our development of the connecting rods, we once again failed to remember these oil jets and left out any variance of oil delivery to the pistons. A loud knocking noise in both engines nearly simultaneously alerted us to the problem. At first we though it was rod bearing failure due to lack of clearance, but instead, we found seized pistons looking like this. It doesn't take much extra heat to do this.
After nearly a year in delays, reworks, resizing and re-coating, we though we finally had a connecting rod that we could be happy with. The weights of the rods were amazing weighing only 150 grams total, and approximately 29 grams on the small end (reciprocating weight). The rods were light, small and let the engine rev up quickly and freely. However, one little oversight in the manufacturing process flawed these rods to complete failure.
Sharp machining edges were left by the thread cutting process. These edges caused enough of a stress-riser in the Titanium to cause a crack to initiate and eventually fail the rod and destroy the motor. Welcome to the graduating class of connecting rod machining 101 - Design-It Prototype received an "F" on that final exam. G-Force also failed a big test - NEVER EVER go to someone for a high-quality racing part because they're cheaper than the rest. Go simply because they're the best.
No more messing around. We went back to Carrillo where we knew we would get the best rods available with no questions asked. With the experience we just had, we started out with Carrillo's traditional Steel "H" Beam rod. In my 20+ years of building engines, I have yet to see a Carrillo rod fail due to design, material or workmanship. Overall, the rods were about 4 grams lighter than stock.
However, the small end was actually heavier than stock by nearly 8 grams. As my primary goal was to reduce reciprocating weight as much as possible, I was really after something even lighter. Jack mentioned they had a new "Sportsman" or "A" Beam design rod they introduced that he thought he could get lighter on the small end for us, without changing material.
This sounded much more like what I was after, and eventually we did get a set. The original set we installed went with a TTS 444cc kitted motor because the pistons were so heavy I wanted to offset that extra weight as much as possible. Later, the next sets we received were even lighter on the small end. Pictured here is our long-rod 450 stroker rod, so the weight is a little more than a stock length rod, and still lighter than the "H" Beam by nearly 4.5 grams.
The ultimate in rods came after a bit of time. But, they were worth the wait (or is that weight?) Because Jack/Carrillo didn't want us to suffer anymore losses due to product failure (at least directly resulting from their parts) Carrillo over-built their first sets of Ti rods for us. Even with this being said, the rods were almost 40 grams lighter than their traditional Steel "H" Beam rod. This was a tremendous reduction in rotating weight (aka: acceleration).
Again, my ultimate goal was a reduction in reciprocating weight, which they came through for us there as well. The Carrillo Ti "H" Beam rods small end weighed just a few grams less than stock. Not the same weight savings we got from the Design-It Prototype rods, but after several seasons of running these rods, they have not failed us yet. I will accept a little weight penalty for longevity in this case.
The good news is, anyone can get these rods. The steel rods are usually available in approximately 5 weeks. Titanium usually takes a bit longer. The bad news is, due to the high-quality material and manufacturing processes Carrillo uses to manufacture their Ti rods, they run approximately $4,000/set of four. This is actually right in line with other top-end Ti rod manufacturer's prices, so we don't think these prices are out of line.
However, for most of the average racer's budgets, the Carrillo "A" Beam steel rods are the best insurance policy you can buy for your engine at around $1300/set of four.
ROD FAILURE or RIDER FAILURE?
These are photos of the latest 428cc engine failure. Which failed first? In this case, this was not a rod failure at all. The rider, Mark Elrod, while in 2nd place during the last 450 Superbike race felt the power taper off on the engine. What did he do? He pinned it. What it turns out is, the bearing had starved - most likely in a recent crash - and self-destructed over a short period of time. Because of the excitement of the race, and not wanting to lose points, Mark kept the engine pinned until the bearing melted away, putting heat into the rod and extra vibration into the rod bolts until the bolts finally failed after nearly half a lap of riding like this. In fact, the rod itself never failed.