Make or break?Tags : bearings
In NHRA professional drag racing, main and con rod crankshaft journal bearings are among the items that can make or break a run. It stands to reason that when a team finds something that works well for them, they are inclined to leave well enough alone.At John Force Racing, Dean ‘Guido’ Antonelli is one of the crew chiefs for the quartet of Funny Car teams. His prime requirement is tending to Ashley Force Hood’s Ford Mustang Funny Car.Occasionally, when Antonelli misses on the tune-up at the track, he will “Burn the bearing babbit off but won’t hurt the crankshaft,” because of the enhanced MAHLE Clevite bearings he currently uses.
“Clevite Nitro V series bearings maintain that fine line of being hard enough to withstand cylinder pressures of 10,000 psi, yet soft enough to tune the engine.”One key to successfully running a nitro-powered drag racing engine is the ability to “Use the upper rod bearing as a tuning tool. After every run we measure the thickness to see how hard that cylinder was working,” down the 1000-foot drag strip.“For example, the stock shell measures 0.0625-inch thick. If after the run the shell measures 0.0535-inch thick (a difference of 0.009-inch), that would indicate that the cylinder is working harder than we would like so we would make the jet sizes larger in that cylinder.” The opposite would hold true if the shell was squeezed only 0.0005-inch, meaning Antonelli was likely not working the cylinder quite hard enough.Antonelli said that the same style main and rod end engine bearings have been the JFR team’s choice for at least the last three to four years. There have been recent developments to increase bearing life. “We work closely with Clevite to ensure we know as much as possible about the dynamics of our engine bearings, the oil film, the firing load and deformation that occurs to the entire rod-crankshaft-bearing assembly when the cylinder fires,” Antonelli said.Extreme surface damage to a bearing can inflict permanent damage to the crank; materials advancement in Clevite rod journal bearings often allow Antonelli’s crew to “hit the crank with some 400 grit emery cloth, leave it in the car and do battle again.”“If we suffered severe damage to the surface of the bearing, the JFR crew would need to replace the crankshaft. And that [crankshaft] is a $3500 item these days!”The JFR teams carry sufficient main and rod end bearing inventory for five to six events on its trailer. “We change the lower shell on main bearings two through five every run and the upper shell on two and four, then three and five every third run alternating,” Antonelli told me. “The upper rod bearings are changed out every run and the lower (cap) rod bearing every other run.”The MAHLE Clevite bearings used by JFR are widely used in alcohol and nitro-burning NHRA classes. The CB1512V rod bearing is the mainstay for Hemi-powered engines, according to MAHLE Clevite’s Bill McKnight.This bearing has an overlay of Vandervell’s lead indium design with an intermediate layer of cast-copper-lead applied to a steel back. It is specially made for the Hemi engine that is the basis for most nitro-class engines.Two different main journal sizes are available and legal for NHRA nitro classes. About 80 percent of engine builders use the traditional 2.750” size while the balance opt for a 3.00” main. “It is a matter of personal preference,” McKnight said.All the JFR Funny Car teams run the 3.00” mains. The JFR BOSS 500 Ford Top Fuel engine is campaigned by John Force and Mike Neff; Force Hood and Robert Hight currently run the Hemi style engine.McKnight points out that, while the BOSS Ford uses the same 3.00” main bearing journal size as the Hemi, a different main shell is required for the Ford housing bore.“Both the BOSS and the Hemi three-inch shafts utilize five straight-shell bearings and thrust washers instead of a flanged thrust bearing,” McKnight noted. The thrust washer (TW120S) is the same for both the Ford and Hemi three-inch mains.