The following information supplied by Marzocchi in Feb.1986
and should be use for the 1989-90 Ducati 851 and SP versions,
Bimota DB1, S, SR series motorcycles.
This what I have found and what actually worked well for me (170 lbs)
And my son (120lbs).
GENERAL INFORMATION
The right fork assembly controls rebound (knob at the bottom of the fork slider) and the left fork assembly controls compression (no control anywhere).
Different levels and different viscosities of oils can be used to suit conditions. This is the beauty of these forks. Adjustments on each leg will not effect the other. Only fork springs and oil levels need to remain the same. Oil viscosity can be varied on each leg if you are competent enough to judge and appreciate the differences.
Fork Springs
There seems to be misleading and inconsistant information on the springs for the M1R forks. There are 2 springs, one in each leg. Some parts breakdowns will only show one and even Marzocchi literature is misleading when it actually shows NO SPRING in the crossection of left fork tube. Trust me.......there ARE 2 springs.
Marzocchi has different fork springs for the 42mm M1R forks which are:
Light Spring-------30 inch/lbs---------Part # 18.0071
Medium Spring ---40 inch/lbs---------Part # 18.0072 (standard)
Heavy Spring-----50 inch/lbs---------Part # 18.0073 (standard)
Progressive Suspension has springs (Part # PS 1130). They work extremely well especially with the adjustable preload caps (no Part #) on pg. 7 of the Pro Italia, June 1994 catalog. These adjustable caps were made for the Ducati 750 Paso and the 907 Paso.
FORK TUBES
It appears that the right and left fork tubes are of different lengths as supplied on a motorcycle and there are different lengths available.
YOKES (Triple Trees)
Different offsets and stem diameters are available.
OIL LEVEL(s)
The oil level is measured from the top of the open fork tube (cap off) to the centerline (repeat: centerline) top of the oil inside the upper fork tube. Take the springs(s) out and compress the fork completely to
Make this measurement.
38mm tube models should have 160 mm of air distance from top
42mm tube models take 170mm of air distance from top.
I recommend you buy one of the many availble fork oil measuring tools that look like a very large medial syringe with a long tube where the needle would be. On that tube there is a sliding disc that will rest on the top of your fork tube. The idea is to put a large amount of oil in the tube and then(with the tool) you suck off the unwanted oil and then repeat for the second tube. Simple and very accurate.....IFthe forks are vertical.
Use 5 weight oil for temps 10-15 centigrade (30-50 F)
Use 10 weight oil for temps above 15c (50 degrees F )
Adjust the oil viscosity to suit temps. There is 2 wt oil for colder temps and you can "play" with mixtures as you desire and learn.
The right fork leg with the knob down on the bottom is for REBOUND and has 4 (yes only 4) positions. You can rotate past 4 and will go back to 1 after you get the oil and spring(s) installed you should be able to tell the 1 position from the 4 position.There are different springs in the REBOUND adjustment (knob area) to adjust the range of rebound dampening rates (not to mention you can play with oils).
Light rebound: Spring # 71.0050
Medium rebound: Spring # 71.0051 (nromal)
Heavy rebound: Spring # 71.0052 (normal)
Use no air in these forks. From time to time you will need to bleed off unwanted air that gets trapped in the forks.
MODIFICATIONS TO FORK LEGS (Tubes)
In March 1986 a Marzocchi service bulletin recommended:
Left tube: drilling a 6mm hole, 65mm from the bottom of the fork tube
Right tube: drilling a 6mm hole, 35mm from the bottom of the fork tube.
BE CERTAIN TO "DEBUR" THIS HOLE AND SMOOTH EDGES OF
DRILLED HOLE AS BEST POSSIBLE.
ricambi.spa@marzocchi.it has the Marzocchi service manual & parts book (one book) and spares.
