Twin Cam B-Motor Balancer Mods
For the 2000 model year, Harley-Davidson introduced a redesigned Softail frame. To maintain the visual styling of the Softail models, Harley knew that the Softail’s engine had to be solid-mounted. Harley also knew that a solid-mounted Twin Cam 88 engine would create too much vibration. The Factory’s solution was the new Twin Cam 88B motor.
The Twin Cam B-motor differs from an A-motor in that it has two counter-rotating balancers, one fore and aft of the flywheel assembly, that, together with the flywheels, negate nearly 100 percent of the engine’s primary vibration. The two balancers are connected to each other and the crankshaft by a roller chain. The flywheel’s pinion shaft and each rotating balance shaft have a chain sprocket with a timing mark that must be aligned to correctly position the balance shafts and flywheels for proper engine balance.
The drivechain is kept in adjustment by two hydraulically operated chain tensioners. The engine’s oil pump feeds oil to the hydraulic tensioners through a special oil galley. Three plastic chain guides, two top and one bottom, keep the drive chain running in a smooth arch. The B-motor’s crankshaft assembly is the same as an A-motor’s, except for the right flywheel/pinion shaft unit and the addition of a chain drive sprocket, which is pressed onto the pinion shaft. The entire counter-balancing system adds about 14 pounds to the engine.
For the most part, the Twin Cam B-motor counter-rotating balancer system is relatively maintenance free. However, under certain conditions the chain drive sprocket pressed on the crank’s pinion shaft can slip, throwing the balance shafts out of alignment and the engine violently out of balance. Additionally, when riding on the street and suddenly closing the throttle, a B-motor can cause a “pushing” effect, which can require more braking than desirable.
Charlie Lawlor of Short Block Charlie’s in Tempe, Arizona, has developed two modifications that fix both balancer problems while improving engine acceleration. To address the engine’s out of balance problem caused by the drive chain sprocket slipping out of alignment on the crank’s pinion shaft, Charlie TIG welds the chain sprocket to the shaft. To eliminate the engine’s “pushing” effect, Charlie reduces the weight of the steel rotating balance shafts and matches their individual weights to closer than Factory tolerances. The two modifications smooth out the engine, allow for faster acceleration, and reduce the “pushing” effect while providing a more durable and worry-free engine.
Charlie can perform these worthwhile modifications on a new “crate” engine, used engine, or engine damaged with skewed balancers or a shifted crank. Of course, since the crankcase must be disassembled, these modifications are best done when doing major performance work like installing a stroker crank or big-bore cylinders requiring case machining. For additional information on building a bullet-proof bottom end, check out the companion article in this issue of HOT BIKE that explains how to improve bottom end durability by installing a left-side Timken bearing in ’03 and later Twin Cam engines.