31.5 forks.

[Bevel bob]

I have a pair of forks i am working on that came from a Motobi Catria 175 late 50's probably. They appear to be Marzocchi although a bit different from the NC forks in the internals. Any idea if seals can be obtained at reasonable cost and the likely quantity of oil needed.

[Bevel bob]

Also any info on the assembly as otherwise its a guess.!!.

[themoudie]

Aye Bob,

Nigel has 31.5mm seals in stock #GS-10310, maybe able to help with exploded diagrams.

This is a link to a 1962 Road Test by Cycle World:Motobi-175-Catria_road_test

This is another link, this time to Motorcycle Classics. The reeason for posting is that they appear to have obtained their details from the machine in the Barber Motorcycle Museum (BMM). So, maybe the BMM would oblige you with technical information, if you contacted them? Worth a try!

Link: Barber_Museum_1957-motobi-catria-lusso-175

I hope this helps you make some progress with Laurie's ex-baby.

Good health, Bill

[Bevel bob]

HI Bill, I am very much on my own with this one!, No info and no spares. I think the forks will have to be machined to take later seals as the std parts are more dust wiper than seal. Tubes will need grinding and a chrome to make servicable, Sliders very worn ,may have to be line bored and sleeved.

[George]

Hi Bob have you tried the Benelli Motobi club GB

[themoudie]

Morning Bob,

HCP have always done me a proper hard chrome plating job on stanchions that I have sent them and at reasonable cost too, I also know of others who have used their services, with positive results.

Link: Hard_Chrome_Plating

As for the line boreing etc have a word with Pat at Seager Engineering, Suffolk, they have a page on this 'ere Facebook thing!

Good health, Bill

[Bevel bob]

Hi Bill, Got the forks fully dismantled. I cant for the life of me see how the damping could work ! But they won championships on these forks so perhaps something is missing. There is a small circular valve with about 9 holes, on the NC forks a similar device had retained balls in these holes and worked once i had fitted the missing ball bearings and spring . Getting relevant information is going to be key. Lots of these bikes went to America so perhaps there is someone over there with info. Any idea on quantity of oil in the early Ducati forks?. I am told they are similar to 175 forks but they are certainly different to my Mach ! type forks. i am guessing 110 ml oil

[themoudie]

Aye Bob,

Do you have a Clymers Ducati single manual?

If not I will see what they suggest in one of mine.

Alternatively, Nigel is selling this manual that might be of use for some of the chassis parts, including the forks.

Link: Ducati_workshop-manual-100-125-175-200

I too would contact the Benelli/Motobi Club UK as they appear to have manuals etc.

Link: Benelli/Motobi_Club_UK

Hope this helps and good health, Bill

[Bevel bob]

Hi Bill, Yes i have the Clymer book and all the other books !. I think I have worked out how the fork damping works . Rebound damping only and its dependant on air being trapped above the damper to push the oil back around the valve . The fork top fixing has to be airtight otherwise the oil is just pushed up and down and not utilized . Also dirt in the system stops the valve sealing on rebound. And there was 50 years of that.

[themoudie]

Aye Bob,

The fork top fixing has to be airtight otherwise the oil is just pushed up and down and not utilized . Also dirt in the system stops the valve sealing on rebound. And there was 50 years of that.

That would have been a pogo stick that Laurie and you were riding then!

I hope that you are able to get the forks sorted.

Pre-TT Classics on the radio, this afternoon and tomorrow!

Good health, Bill