Hy-Vo For Motorcycles

HY-VO FOR MOTORCYCLES

A NEW TYPE OF PRIMARY CHAIN WITH GREATER EFFICIENCY, LESS NOISE AND VIBRATION, AND IMPROVED RELIABILITY

ORIGINLLY DESIGNED in the late 1940s as a solution to the high-speed, high-load requirements of heavy oil drilling equipment, the Morse Hy-Vo chain has recently been incorporated into the drive train of the front-wheel-drive Oldsmobile Tornado and Cadillac Eldorado. Andy Grana-

telli’s STP-Lotus Turbocar, which came within a hairsbreadth of winning the 1967 Indianapolis 500, also featured a Hy-Vo chain.

A Hy-Vo chain assembly is similar to a ‘‘silent chain” in that it is composed of layers of inverted tooth steel links. These links are laced in alternate sections across the width of the chain, and are assembled with two steel pins—one called the pin and the other the rocker having the same cross-sectional geometry. This forms the joint which articulates between the joining link sections.

One of the major pitfalls of a conventional roller chain is the “chordal action” which occurs as a vibratory motion caused by the chain’s rise and fall over the teeth of a small sprocket. This chordal rise and fall (acceleration and deceleration) of the chain as it passes over the sprockets generates heat, noise and vibration, which seriously curtails the roller chain’s ability to transmit power efficiently and reliably as the speed rises. With the Hy-Vo chain, only small changes occur from the true “involute constant velocity” theory; the resultant benefits are much higher operThe Hy-Vo chain is clearly some 800 percent stronger than a roller chain of the same size!

Honda led the way for the use of the Hy-Vo chain in motorcycles by incorporating it in their new CB500 Four to transmit power from the crankshaft to the clutch shaft. Although only 3/4 in. across, the chain is capable of transmitting much more power than will ever be used.

Almost simultaneously, two firms in Northern California have introduced Hy-Vo chain drives for BSA and Triumph 650 Twins. These chain drive kits consist of a primary drive sprocket, a Hy-Vo chain and a clutch sprocket to fit in place of the standard units. The specifications:

ACK Products, 676 Auzerias Ave., San Jose, CA 95 125, is producing replacement primary drive units for BSA 650-cc unit-construction Twins, the new BSA 500-cc Single and the Triumph 6 50-cc unit-construction Twins. The original primary drive reduction ratio is retained and the drive unit fits in place of the original unit with no modifications.

The clutch hub is machined of 4130 chrome-moly steel and is heat treated by a special process which produces a

hard wearing surface over the entire hub without the distortion caused by normal heat treating processes. The small sprocket is made of hardened alloy steel.

The Triumph 650 and the BSA 500 drives utilize a 0.890 in. wide chain, and the BSA 650 drive features a 1.280 in. wide chain. In addition to these drives, ACK Products will build units for practically any motorcycle now using a roller chain primary drive. Jim Rice, AMA National No. 2, uses the ACK primary drive on his BSA 650-cc Twin.

Titan Products, 20 Mark Drive, San Rafael, CA 94903, is offering a similar set up for BSA and Triumph 650 Twins, with the main difference being the clutch hub, machined from 4340 chrome-moly bar stock. The primary sprocket on the Titan unit, slightly smaller in diameter, gives a primary reduction ratio of 2.4: 1, as opposed to the standard ratio of 2.07:1, and allows the removal of the chain guide. Dick Mann, AMA National No. 4, is a user of the Titan Hy-Vo chain drive. Both the ACK and Titan drives retail for approximately $ 180.

The Hy-Vo, the coming thing in chain drives, may well replace the roller chain in certain applications in the near future. (Ö)

ating speed, smoothness in operation, greater load capacity, silence and greater efficiency (approximately 99 percent).

ASA ratings for the roller chain v\s\ a Hy-Vo chain of approximately the same size, using a 2 5-tooth reference sprocket, are:

Twin row:

3/8 in. pitch roller

chain...............4.79 bhp @ 7000 rpm

3/4 in. Hy-Vo

(0.890-in. wide) .......42 bhp @ 7000 rpm

Triple row:

3/8 in. pitch roller

chain ..............7.05 bhp @ 7000 rpm

1 in. Hy-Vo

(1.280-in. wide) .......56 bhp @ 7000 rpm