Ceriani 38mm stucked piston

michipons

michipons

Hero member
Location
Palma de Mallorca
Hi all!

Today I was rebuilding the Ceriani fork 38mm. (As a preceeding, the fork was the last 30 years on a garage with no movement) when I realized that one side was completely seized. I managed to open it and saw that the piston that I mark on the photo was not sliding at all, finally I removed it, but it doesn't slide in anymore, is like it would be a bit wider. The tube should be ok as the other's side piston slides perfectly.

Did anybody had similar experience? I never imagined that a piston fork could be seized, or even how. I thought may be would be a bit of oxide, but was well oiled so it wasn't the case, I sand paper it a bit but no improvement. As the part doesn't look too complicated, I am considering to make a new one with the turner or correct this one, is that a bad idea? or do you suggest something different? I didn't find this piston as spare part anywhere.

Regards and thanks for help,
Miguel.

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Those pistons swell with time.
You can probably turn that one down on a lathe or make a new one.
Others will know better than I.

Paul
 
Yep. Make a new piston from some aluminium bar. I make them with about 0.05mm (2 thou) clearance. You can get away with small clearance because the billet aluminium won't swell and stick in the fork leg like the old pistons, and the closer fit they are the better the forks will work.

The internal diameter of Ceriani fork tubes can vary quit a bit (I guess quality control wasn't as good as it could have been) so if you use close fitting pistons, they will need to be individually fitted to their mating fork tube. I suspect that was never done in the factory, and they just went with a "one size fits all" piston diameter. It would have been a sloppy fit in some fork legs and tighter in others.
 
Hi!

just to close the topic, I finally brought the piston to my turner, he corrected the piston within 10 minutes and was working nicely again! cost 20?. 40 years old fork back into service 8)

thanks for help!
Miguel
 
agree, it is some strange alloy, the magnet attaches but very weak. The turner looks me allways with questioning eyes.... "What strange shit is he going to bring me today??" So I try to combine profit work with shity things like that. So before he makes me this two pistons new, I will have to order him a head cylinder rebuild or something... :D

but is on my todo list to make a few new pistons...

regards,
Miguel
 
Let?s not blow things out of proportion. Ceriani suspension, especially the type used with disc brakes, was the highest quality that was available at the time, and I for one never needed to replace a piston in any of my Cerianis.

The only part that tended to wear out in certain forks was the brass ring, resulting in diminished rebound damping. In my 1975 3C they were worn out within 10.000 km, in my 250.000+ white SF2 they are still fine.

Marnix
 
The pistons in my forks were swollen and cracked and the guy I had lined up to make new ones had to isolate himself when covid kicked off, so I bought some from Bevel Heaven in the USA. They took a month to arrive in the UK and then one fitted fine and the other didn't so I had to find another guy to sort it out.
There must have been a reason they chose that weird alloy, Cerianis were good forks.
 
metal swells quite a bit, we see it with boats a lot, especially hydraulic vang cylinders, that's why when we service them we frequently put in new pistons
 
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