Bearing the load
“It is always a battle for our engine bearings,” says John Medlen, tuner for John Force Racing Funny Car driver Mike Neff in the NHRA’s Full Throttle Drag Racing Series. “Their survival is predicated on the cylinder pressure applied to the bearing and the manner in which we see a rise in that cylinder pressure. We have to look at the pressure curve,” he said.
In all the nitromethane-burning NHRA classes, it’s “okay to have a high and long cylinder pressure curve, but when we experience detonation, it goes right off the map,” Medlen explained. He likes to see about 12,000 PSI, “but when it detonates the cylinder pressure spikes to 26,000!” Every bearing manufacturer has methods of dealing with this cylinder pressure. “It depends on the material.”
Medlen uses a three-layer ‘V’ bearing rather than an ‘M’ series unit. “It’s all about balance. A bearing that is too hard ends up hurting the crankshaft and one that is too soft won’t withstand the loads we see in our engines. We have to get the maximum out of the bearing without killing the crank; it has to be durable enough not to overheat the crankshaft and hard enough to last under these severe conditions” of a 1000-foot trip down the dragstrip in just over four seconds.
The ‘V’ bearing is stronger and has more density to give support to the crankshaft. The lead-iridium surface layer provides both embeadibility to hold trash and flexibility to handle crankshaft and housing bore deflection seen in these conditions. Most nitro runners are using the V-series of engine bearings these days and most, like Medlen, swap out their uppers every run. “We swap out the lower bearings every 6-8 runs,” he said.
The latest development from Mahle Clevite is in coatings. “They have a proprietary coating that keeps the surface temperature down and doesn’t erode the bearing,” Medlen said. He used bearings with this coating for the first time at Seattle on Neff’s car and also in the A Fuel dragster category, where Courtney Force won her first Wally. “We are pretty excited about what we see,” Medlen said.
While the coating is not necessarily new, this is the first time it has been used in the nitro-burning categories. This manufacturer experimented with dry-film bearing coatings on nitro engines but found the standard bearing coatings used so successfully in NASCAR and other racing venues were unable to withstanding the extreme wiping action of the crank. “The standard coating was often completely gone in one pass,” said company spokesman Bill McKnight, “making its effectiveness questionable at best.”
Working with coating supplier H.M. Elliott Inc., the well-known bearing manufacturer has developed a “new coating” that is substantially more durable and shows real promise to bearing and crankshaft life extension in nitro-powered machines. “Our initial feedback has been extremely positive. The new coating is far more durable and we’re pretty excited about the possibility of offering a better bearing to this select group of customers.”
In addition to Medlen, Jim Oberhofer of Kalitta Motorsports, perennial Top Alcohol Funny Car champion Frank Manzo and Terry Haddock, owner/crew chief/driver of his own Top Fuel NHRA dragster have been making test runs with these coated bearings.
McKnight anticipated testing and development continuing into the autumn racing season with the possibility of having the new coated bearings available to all customers before the Auto Club NHRA Finals at Pomona in November.
Written by Anne Proffit.