1972-75 Cush Drives

What's the Difference?

by Alan Buehner

Originally printed in the 2006 issue #35 of Still….Keeping Track

The purpose of this acticle is to show and explain the differences between the 2 sizes of cush drives and their parts used on the 1972 thru 1975 Penton 100 & 125s, and the 1972 thru 1973 Penton 175s.

The small size cush drives were used on all the 1972 model year bikes. This worked fine for the 100s and 125s but the 175s had too much power for small cush drives to handle. When the cush drive rubbers wore to the point where there was back and forth play between the sprocket backing plate and the hub, the torque from the 175s would shear off the tits of the hub.

The fix for this problem was 2 fold. The
first was to increase the diameter size of cush drive rubber. The second was to remove the cush drive units from the 175s in 1974 and bolt the sprockets
directly to the rear hub as was done with the 250s when they were developed in 1973.

The sprocket carriers show the most obvious difference which is the I.D. for the 6 cush drive rubbers. But, there are 2 other differences.

The first is the center hole for the bearings. The New Style carriers use larger diameter bearings to deal with the stress applied to them by the engines. (Note: the bearings in the sprocket carriers will wear out faster than the rear hub bearings).

The second difference on the sprocket carriers is the thickness along the outside edge. The 100s and 125s use 428 sprockets and the 175s used 530 sprockets. The 530s are thicker than the 428s and to compensate for this, all the 17 5 sprocket carriers were milled down to keep the rear sprocket in line with the drive sprocket.

The axles are different as can be seen with the new style being a 2-step for the two different bearings.

The snap rings are different diameters to fit the openings in the carriers.

The larger cush drives were developed by 1973 to fix the 175 problem. The larger units were put on the 1974 production year bikes (100s and 125s) as soon as the supply of small cush drive units ran low. As a result, it helps to know the difference when restoring and repairing these bikes so one knows which unit that they have and what parts are needed.

The most obvious is the cush drive rubbers. The small size measure 23-26mm O.D., the large size measure 32-34.5mm O.D. If you can put your index finger through it, you have a large size cush drive.

The following is an explanation of what some of the other differences are: