The Crankshaft Process After the grinding is completed, the crankshaft goes through severa
Bob Koch, owner of Race Engineering, says that in addition to the reduced friction, smaller journals also have another advantage. "Not only do you get less bearing speed, you are reducing your weights," he says. "The reduction on the crank side is obvious, but it's also minimal. It's the reduction in the rod weight that can be important. If the rod manufacturer does the job properly when they make rods with smaller journals, they will move the bolt locations inboard. Then, they can machine some of the steel off from around the pads where the bolts go, which gets rid of weight."
Even though this reduction in weight can amount to just a handful of grams, you have to consider the location. Because it is away from the crank centerline, this weight is critical. Plus, removing it also reduces the bob weight, allowing the counterweights to be smaller, too.
Smaller main journals also offer the same benefits for lowering the bearing speed. The problem is most of us cannot simply order a custom engine block, and most are made with standard main journal sizes. As a fix for this, Race Engineering offers bearing spacers which allow a small-journal crank to work in a large-journal block. The spacer looks a lot like a bearing that another bearing will fit into.
"A lot of guys will tell you that's not the smart way to do it, and they are probably right," Koch says. "You really don't want to throw another piece of steel into the engine [if you don't have to]. But if you have a large-journal block and want to go with a smaller journal crank, this will let you do it-and it works. You just have to watch your clearances like you would with any engine build."
For situations where you may want to use a crankshaft with small main journals in a block
Windage Simply put, windage is the power loss caused by oil splashing against or clinging to the crankshaft as it spins. Windage is a concern in any race engine, but it's especially important to try to minimize it in a wet sump engine. Good oil control begins with a quality oil pan and scraper, but crank design can also help. Racing cranks generally feature narrower counterweights and, when rules allow, a shaped leading edge on the counterweight. Instead of a flat edge splashing into oil, a curved leading edge helps reduce the impact of crank against oil. Interestingly, representatives from both King's Crankshafts and Scat both stated during our interviews that they do not recommend knife-edging the leading edge. Instead, they prefer a rounded leading edge (also called a bullnose).
"The knife-edging takes a lot of weight out of the leading edge of the counterweights, which will make the crank more difficult to balance," King explains. "Plus, depending on how much material you remove to create the knife edge, the bearings also won't wear as well."
One of the greatest challenges we face when guys build their own engines is getting them to understand that snap gauges just do not work. That is one of the first things we ask when a guy calls us and tells us it got too hot on one of the mains. To everyone planning to build their own engines, I recommend spending a little money on a dial bore gauge. Then, they know they can do all the clearances correctly.-Rick King, King's Crankshafts
One interesting thing that the Nextel Cup guys have learned recently is that at high-rpm levels, overbalancing can cause problems. It's common to overbalance, or add balance weight to the counter weights, at 51 or 52 percent. What we didn't realize is that as rpm goes up, those counterweights get heavier and heavier through centrifugal force.
So, the Cup guys, once they went from 8,500 to 9,000-and even 9,200 rpm-started scuffing bearings. And they couldn't figure out why. Evidently, one guy said, "Let's try something different. Let's cut the counterweights off." I'm using that very loosely, but what they did was turn the counterweights down and then add heavy metal to get the mass back up. All of a sudden, the problem started to go away.