ceriani 38mm front forks - seized up!

Laverdaton

Laverdaton

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In the garage deciding what to do first!
I recently bought some seized front forks,
I've managed to get them completely stripped down and the cause of the seizure is the white nylon sleeve that is held in place by a circlip on the long oil pipe at the bottom of the stanchion.
The white sleeve is 0.5 mm bigger than the bore diameter of the fork tube, 32mm.
I had to use a wooden broom handle to tap the nylon sleeve and the oil pipe out of the bottom of the chrome fork tube.

What clearance should there be to allow the fork tube to travel up and down the sleeve?
Andy
 
Never seen a nylon bush on Cerianis.

Will be getting a pair of 38mm 750 Cerianis this weekend that I'll be selling on.

Paul
 
That's the piston. As others have said, if yours is plastic it's non original. The factory made them from some crap aluminium alloy, which also tended to swell up and jam. So it's not surprising that someone has replaced them, but plastic is perhaps not the best choice of material. It's not dimensionally stable, especially if it warms up a bit.

It should be a clearance fit, but only just enough clearance to allow it to slide nicely in the fork tube. Quality control was a bit iffy on those old Cerianis, so fork IDs and piston clearances vary quite a bit.

I machine my own pistons from billet aluminium and match them to each individual fork tube with 0.05mm clearance. I'd offer to make you some, but I'd need the fork legs to match them to. Find a machine shop in your area and ask them to do it for you. It's a simple job so won't cost an arm and leg.
 
New stanchions have a slightly smaller ID than the original ones.
So the original pistons have to be machined a bit.
Maybe that's where the problem came from.
DPO bought new stanchions and had some nylon at hand...

Ernesto
 

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That's the part!
Can anyone tell me the depth of the piston...I'm hoping someone has a fork leg stripped down - I'll get a couple made up to suit the fork legs.
The part is identifid in the parts list picture from Andy Wagner but there is no part available.
Thanks to all who replied....
Andy
 
Andy, I will strip down a pair of 38mm Cerianis tomorrow or on Sunday.  I'll measure the piston and put in the results here, in case no one else will step in earlier.

Regards,
Stefan
 
Here's a drawing I prepared earlier ?
(PDF file attached)

It'll print on A4 at very close to actual size, although the scaling may vary marginally between printers. Anyway, it's good enough to take to an engineering shop.

PS: I make the piston wall a bit thicker than the original at 4mm (original is 3.5) just to give it a bit more rigidity.
 

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