Fitting together the Power Puzzle, Part 3: Rods and pistons
5/16/2006

 

Building a 330-mph, 7,000-horsepower, nitromethane-churning Top Fuel dragster or Funny Car is sort of like putting together a puzzle;  if one piece is missing, it doesn't work. That's why each crewmember plays a vital role in making sure that the cars not only meet NHRA's strict tech requirements, but that they're also race-ready to blister the quarter-mile.

In this eight-part NHRA.com series, the Don Prudhomme Racing crewmembers on Larry Dixon's Miller Lite Top Fuel team will take you behind the scenes into their world and provide a closer look at what role each person plays on the race car.  The third part of the Power Puzzle series looks at "racks," or the rod and piston assembly. A new rack is placed into the motor following each quarter-mile pass, so it's another important element to the 7,000 horsepower riddle. Anthony Vanetti is in charge of assembling and servicing the rods and pistons.

 
Vanetti, 29, spends plenty of quality time in the Miller Lite hauler with the JE pistons and Brooks rods. The Northern California native and aspiring Pro Stock Motorcycle rider joined Dixon's pit crew late in the 2001 season and was a vital part of helping the team win consecutive series titles (2002-03). Along with rod and piston assembly duties, Vanetti mounts and balances tires and is the bottom-end man on the Miller-backed rail. You'll learn about the "diver," or bottom-end guy, in a future edition of the Power Puzzle series.

 
During the post-run service, the rack is removed from the engine. Once the rods and pistons are taken out of the motor and placed in the rack tray, they're taken into the hauler so that crew chief Don Bender can survey the rack and check the rings (Perfect Circle) and bearings (Clevite) after a run. He examines the ring tightness and width of the bearings. Following the quick inspection, the rack is taken to the solvent tank for a thorough bath. The clean rack is then disassembled so the parts can be examined to find out if they're capable of being used again or should be placed in the junk pile.

 

The rod and piston assembly consists of the rod, piston, wrist pin, two buttons, two compression rings, two oil rings, and an upper and lower bearing. First, Vanetti checks the wrist pins to make sure they're within spec and not too out of round. They can lose form when the engine drops a cylinder.

Next, he places the rod cap on the rod and torques it together just as it would be in the motor to check for gaps, a process called "spreading the forks." If there is a gap, the rod goes into the scrap pile. If the rod passes the cap test, he checks both the small (wrist pin) and large (crankshaft) holes to make sure they're within spec. If it passes the first two steps, then the rod is measured for straightness.

   
Next, the cap is removed from the rod and the rod is checked for length variance, which affects the compression height of the motor. Once the rods are complete, Vanetti moves on to the pistons.

He starts by checking the wrist pin hole on the piston. The compression and oil rings have already been examined, and the pistons with the tight or stuck rings have been weeded out of the bunch. Next, he measures the skirt of the piston. A piston that has been used on a number of passes is often squeezed at the skirt and/or depressed at the dome. If the skirt or top of piston don't meet the requirements, it's thrown out. It takes Vanetti 45 to 50 minutes to service a rack following a run and 20 minutes to assemble a new batch of rods and pistons.

"The racks are quick and easy to build once you develop a routine," Vanetti said. "The majority of the time is spent checking parts to make sure they're within the required specs. Once the parts are checked, the racks go together quickly."

The Miller Lite team carries nine race-ready racks to each event, along with the rods and pistons that are in the team's legion of short blocks. In the service process, the oil rings are changed following each pass, and the compression rings are replaced if they're scuffed. Upper rod bearings are swapped following a run, and the lower bearings are exchanged every second pass.

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