Cerriani Fork Tube Nuts

What's the Difference

by Alan Buehner

Originally printed in the 2009 issue #42 of Still….Keeping Track

The purpose of this article is to show and explain the differences between the different fork tube nuts that were installed on the Cerianni forks - used on the Penton brand of motorcycles from the years 1968 thru 1975. These were used on the standard forks with the axles on the bottom of the fork legs (before the leading axle forks). The steel tank Pentons (1968 thru 1971) came equipped with the short 35mm Cerianni forks. The CMF 100, 125, & 175 Pentons (1972 thru 1973) came equipped with 32mm Cerianni forks. The 1973 thru 1975 CMF 250s & 400s and 1974 thru 1975 100, 125, & 175 Pentons came equipped with the long 35mm Cerianni forks. There is a difference between the short and long 35mm fork tube nuts.

A. The early 1968 thru 1971 35mm fork tube nuts are short in length - measuring 33mm in overall height. The recessed area that goes into the fork tube measures 21 mm. The hex part measures 29mm.

The fork tube that is used with this nut is squared at the top and is secured in the top fork plate with the nut and is pinched with an alien head bolt in the top fork plate.

The Penton part number for this nut is #1-39-000.

B. The 32mm fork tube nuts are short in length - measuring 31mm in overall height. The recessed area that goes into the fork tube measures 19mm. The hex part measures 24mm.

The fork tube that is used with this nut is squared at the top and is secured in the top fork plate with 2 alien head bolts that pinch it in the top fork plate.

The Penton part number for this nut is #1-503-021.

C. The 1973 thru 1975 35mm fork tube nuts are longer in length - measuring 39mm in overall height. The recessed area that goes into the fork tube measures 27mm. The hex part measures 29mm and is over sized, extending over the holes in the top fork plate.

The fork tube that is used with this nut is tapered at the top (as shown in photo) and is secured in the top fork plate by the nut which pulls it up tight into the top fork plate.

The Penton part number for this nut is #1-622-021

D. There is a vent system using a small pin hole in the bottom and a side hole exiting out the top side of the hex. A 4mm ball blocks the pin hole in the bottom and a spring applies pressure to the ball. A tapered screw secures the spring and ball. Excess pressure created in the fork tube is vented out through this valve set-up.

It is important to check that the ball and spring are not rusted out and that the side vent is not blocked by dirt. A non-functioning vent will cause oil to spray out of the fork seals.