obody’s perfect. For instance, as much as you enjoy their company, even your best riding buddies may have traits that drive you nuts. The same goes for motorcycles. As good as Harley-Davidsons are, they’re not perfect, either. One of their little quirks that drives riders nuts is the tendency to blow oil into the air cleaner.
     That oil finds its way to the air filter when the oil-saturated air in the crankcase is forced out on the pistons’ downstroke. It’s routed up through the pushrod tubes into the rocker boxes where a foam filter and a rubber flapper valve separate the oil from the air and allow the now-clean air to escape into the air cleaner. But as the miles pile up, both the foam and the flapper valve wear out, and less oil is extracted from the crankcase gas. The result is oily air in the air filter.

Pro-Vent rocker covers efficiently remove suspended oil from crankcase air for years.

Pro-Vent rocker boxes use a series of machined labyrinths to collect oil droplets as breather gasses traverse the passages at high speeds.

     TP Engineering’s answer is the Pro-Vent rocker box. Instead of wear-prone rubber parts, the Pro-Vent rocker box uses a series of machined labyrinths to collect oil droplets as breather gasses traverse the passages at high speeds. Here’s how it works:
     As the oily air is created and forced out of the crankcase, it’s blown into the cam chest, through the pushrod tubes, and into the first chamber of the Pro-Vent system via three entry holes that begin the process of extracting oil droplets from the vapor. Each surface touched by the breather gasses collects suspended oil. The air collides with the walls of the chamber and is forced to make a series of turns before climbing the last wall and flowing through the entry hole into the next chamber. In the second chamber, the breather gasses spin and collide with its walls, and by the time the air climbs the final wall on its way out of the chamber it’s free of oil and ready to enter the crossover channel in the rocker box cover which routes the air out of the head and into the air cleaner.
     Because there are no rubber parts to wear out, Pro-Vent rocker covers remove suspended oil from crankcase air as efficiently after years of riding as they do on day one. There’s a performance benefit to the Pro-Vent system, too. Because the Pro-Vent system cleans the air leaving the engine so well, it allows the elimination of the timed rotating breather valve assembly in Evos driven by the camshaft for the additional benefit of reducing moving parts and decreasing crankcase pressure by 2 psi.
     TP Pro-Vent rocker boxes are machined from 6061-T6 aluminum billet, and the rocker shaft stanchions are an integral part of the rocker box base. The rigidity of this design significantly quiets valve train noise characteristic of Twin Cam engines.
     The Pro-Vent technology is found on all TP Engineering engines. Now your customers can have it on their bikes, too. Just ask your Drag rep for the details.