April '20

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APRIL 2020 THE SHOP 37 PRECISION ENGINE inch hole in the valve cover) sealed with an Earl's screw-in cap. In order to plumb the vacuum hoses to the valve covers, a –12 male weld-in fitting was needed on the front wall of each valve cover. A 3/4-inch hole was drilled, and the male weld-on fitting was surface-mounted to the valve cover wall. Depending on the specific style of bung, TIG welding can be performed at the out- board or inboard side of the valve cover wall. For the small-block example, our bungs featured an external hex. In order to avoid disturbing the hex, we TIG welded around the perimeter of the fitting at the inboard side, placing the weld on the inside of the valve cover to hide it for a neater appearance. REAR MAIN SEALS When running a vacuum pump, standard rear main seals are usually adequate, but for added insurance you can run a special rear main seal that's designed to better accom- modate the vacuum pull in the crankcase. For a small-block Chevy using a two- piece rear main seal as one example, a Fel-Pro 2912 is recommended (2918 for big-block Chevys). Eliminating potential oil leaks is critical when running a vacuum pump in order for the pump to do its job. While often overlooked, consider the dipstick. It's important to use a dipstick that seals. A dipstick that features a sealing O-ring or screw-in style is recommended. If the dipstick does not seal, a vacuum leak can easily result. When using a toothed belt drive system, a mandrel and drive pulley is installed to the crank snout. The pump manufacturer will offer all of the parts needed for a spe- cific application. Kits, such as those offered by Jones Racing, include the mandrel, hub, pulley and a selection of spacers to achieve a par- ticular engine setup that allows adjustment of all pulleys for proper alignment. In order to achieve fine-tuning of the vacuum pump's pulley to the pump's drive pulley on the crank mandrel, loosen three set screws in the pump's pulley and you'll be able to slide the pulley fore/aft on the pump's shaft for perfect belt alignment. Once alignment is determined, tighten the set screws. Access holes in the pump pulley allow easy entry for a hex wrench for servicing the set screws. Routing the plumbing for the vacuum pump was super simple. I made a pair of –12 hose assemblies using 90-degree –12 AN hose ends at each end of the two hoses. The two outlet ports on the pump are plumbed directly to the –12 male weld-in fittings on the front face of each valve cover. The single outlet (exhaust) port from the pump can be plumbed to a remote breather/catch can. Assembly of the –AN Here's an oil fill bung and cap on a small-block Chevy fitted with Moroso fabricated valve covers. In this example, a Jones Racing bung and cap were installed. This bung required a 1-5/8-inch hole. Each bung example shown here was TIG-welded at the under- side of the valve cover roof. In this small-block Chevy example, both a vacuum pump and a racing alternator are belt- driven by a radius tooth drive system. Since the valve covers will not be equipped with breathers, we still need an oil fill port. A threaded bung is welded to the roof of one valve cover. Shown here is an Earl's bung and cap. Installing the bung required a 1.800-inch diameter hole in the valve cover top.

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