Being partially anal and mostly paranoid, I decided to create a mold of the journal’s profile in order to double check the clearances. This was done using CutterSil, a substance that everyone has fallen victim to at one time or another. CutterSil is a pharmaceutical grade silicon that dentist use to create those highly accurate molds of your mouth that leave you sitting awkwardly speechless in a dentist chair for 20 minutes while precariously breathing through your nose. In the automotive industry, we’ve found this stuff to be a pretty handy tool for reverse engineering, inspection, and shutting up loud mouth internet bullies and bench racers who like to pick on girls.
After the CuterSil mold cured, we removed it from the B18C1 crankshaft journal and then cut it apart into a cross section. We then used an optical comparator to identify the various radii that blended the rod journal to the crankshaft cheek using a combination of radius templates and linear measurements to identify their centers.
Now armed with more precise information, I modeled the B18C1 rod journal radius using SolidWorks and then created an assembly model using a QR25DE connecting rod and journal bearing. To reduce friction, the connecting rods in many race engines are piston guided with the small end of the connecting rods being guided by the piston’s pin boss towers. However, most OE engines use crank guided connecting rods, which are guided axially by the machined cheeks (or sides) of the crankshaft’s counterweights. This was the case with our B18C1 engine, so we placed the K1 connecting rod against the crankshaft cheek in the assembly model to verify the clearances between the QR25DE connecting rod and the B18C1 journal radius.
Aside from that fact that I am a complete dork who may need to get out a bit more, my paranoia and suspicions were also confirmed. Even with the generous chamfer around the big end of our QR25DE K1 connecting rods, the connecting rod big end face would contact the journal radius instead of mating flush against the crankshaft cheek. Even worse, the QR25DE rod bearing was able to contact with the journal’s radius, which could easily spell disaster in the form of a spun rod bearing. The only real choice was to decrease the journal radius. However, doing so might compromise the strength of the crankshaft.