Building A Stout Twin Cam Crank

Modifying the Crankshaft
In order to properly modify a Twin Cam crank to eliminate twisting, you have to start out with a crank in good condition. It is best to begin with a new crank, but a used one in good condition can also work. Charlie starts by checking the crankshaft assembly for true and makes any necessary adjustments so there is no more than .001 inch runout on the mainshafts. Next, the crankpin is TIG-welded on both ends to the flywheel halves, and then the crank is retrued to within .001 inch or less. The photos show Short Block Charlie TIG-welding the crankpin on a new Twin Cam stroker crank.

If your engine has experienced a twisted crank, most likely the oil pump has been damaged as well as the cam support plate. If those parts need replacing, it is a wise idea to replace them with the 2007-later (2006-later for Dynas) high-volume oil pump and a compatible cam support plate. Since a damaged engine must be disassembled, this is the perfect time to make engine performance upgrades, such as a stroker crank, big-bore cylinders, head modifications, and high-performance cams.

Cam Drivetrain
Regarding the camshafts, you have a choice of either sticking with chain-driven cams or switching to gear-drive versions. Chain-driven cams use two chains and either two spring-loaded adjusters with flat silent chains ('06-earlier) or two hydraulic operated adjusters and roller chains ('06 Dynas and all '07-up). The hydraulic adjusters are an improvement over the earlier spring-loaded style, but both designs have limitations. The early style spring-loaded tensioners are notorious for experiencing premature wear on the chain pads. Typically, 18,000 to 25,000 miles is the maximum you'll get on a pair of spring-loaded pads. Also, the debris from the pads can clog internal oil passages. The verdict is still out on pad wear for the hydraulic tensioners. Andrews Products is offering a conversion kit to upgrade '99 to '05 silent chain Twin Cams to roller chain drive.

Another concern with chain-driven cams is accurate cam and valve timing. Some high-performance cams require higher valve spring pressures to control valve float and bounce. Since higher valve spring pressure places increased loads on the camshaft, greater demands are placed on the stock chain tensioners. As a result, the tensioners can become overloaded while chain stretch increases, leading to inaccurate cam timing.

Gear-drive cams from Andrews Products and S&S Cycle eliminate the structural problems associated with stock chain tensioners while producing more accurate cam timing. But keep in mind that gear cams must be checked for proper gear clearance. A fit too tight will produce a whine and can destroy the gears in short order, while a loose fit results in gear clatter. Gear cams are less tolerant of a shifting crankshaft than chain-driven cams because proper gear clearance must be maintained. This is an additional reason to TIG weld the flywheel's crankpin when installing gear cams. In fact, some aftermarket shops are hesitating to install gear cams unless the crank is properly modified to minimize the potential for shifting.

Summary Thoughts
The Twin Cam is an excellent engine and includes several refinements over the Evolution, including stouter engine components and the potential for increased displacement. However, to realize its true potential, the Twin Cam requires a few key modifications to eliminate the weak links. The modifications start at the crankshaft and extend to the cam drivetrain.