How to Replace Harley Rocker Boxesby Kyle McBride
Harley Davidson rocker boxes are a three-part aluminum assembly with rubber quad seal gaskets to retain top-end engine oil lubrication. The rocker boxes house the top end of the pushrods, the valve rockers, valve stems and stem seals. They incorporate sound-damping technology to reduce valve-train noise, and can be fitted with chrome or custom boxes adding "curb appeal" to the bike. These boxes can be replaced with basic mechanic's tools.
Replacing the Rocker Boxes
Drain the fuel tank. Remove the fuel tank mounting bolts. Turn the fuel petcock to the "Off" position and remove the fuel line and vaccuum line from the petcock spigot. Elevate the fuel tank (for a one-tank design) and block it up with a wood block. Split-tank designs must have the fuel crossover tube removed and each side of the tank removed completely from the chassis to gain access to the top of the rocker boxes.
Remove the rocker box top cover bolts. Lift off the top cover, middle spacer and associated rubber seals. Place the transmission in first gear and elevate the rear of the bike with a center-stand or bike lift. Rotate the rear tire and observe the valve rocker's movement in the box. Roll the tire until the front cylinder valves are in valve overlap (both valves are depressed at once). The rear-cylinder rocker box is now de-stressed as much as possible and may safely be removed.
Break the torque on the two bottom rocker-box bolts closest to the pushrods, but do not loosen more than a half-turn. Break the torque on the two bottom rocker-box bolts opposite the pushrods and remove them completely. Finish backing off and removing the pushrod side bolts. Back them off, one turn at a time, until the pushrod load is released from the rockers, then back them off fully. Lift the bottom rocker box assembly from the engine.
Scrape any remaining gasket material from the mating surface on the top of the cylinder head. Clean and dry the mating surface, and then install the new gaskets. Tighten the bottom rocker-box mounting bolts opposite the pushrods finger-tight. Insure that the pushrod ends are properly nested into the rocker-arm cups. Install and torque the pushrod side bolts to factory spec, then torque the opposite side bolts to factory spec.
Install the new rubber seal into its groove and ensure that it lays flat and is not rolled at any point. Lay the spacer into position and install the top rubber seal. Rotate the rear tire until the rear cylinder valves are on overlap. The front cylinder will now be in position for removal. Position the top rocker-box cover and reinstall the mounting bolts. Torque to factory specification for your model of Harley. Repeat the process on the front cylinder.
Reinstall the gas tank(s), petcock fuel line, vaccuum line and fuel crossover tube.
- close Test-run the engine without driving it. If there is a leak in the new rocker boxes, the top-end oil will drain down onto the engine and can smoke or vaporize, possibly leading to a fire hazard.
- close Use caution when scraping the old gasket material. The components are cast aluminum and are easily gouged, leading to a chronic leaking condition.
- close Do not remove the pushrod side bolts fully until the opposite side is removed. There will still be some pre-load from the valve springs and the pushrods that will stress and crack the bottom of the rocker box if improperly removed.