851 fork seals - Ducati.ms

alwill923 · Sep 30th, 2007, 6:50 pm

My son has an 1990 851 with Marzocchi forks. We replaced the fork seals a few months ago. He has put a hundred miles on the bike and blew out the right fork seal. this is the one with the rebound adjustment ( only on the right side).

Question - What are the air valves for on the forks? What pressure should be put in? Why would the fork seals blow after a hundred miles? Is the pressure buildingup in the forks? Why only on the right side? Must have something to do with the rebound adjustment?

This is not the first fork seals we have done. We have two race bikes and have never had this problem. We are not fimilar with these forks and would appreciate any help with this problem.

The tubes are not scratched. We are not talking about a weeping seal we are talking about a puddle on the floor.

Thanks

Rduck851 · Sep 30th, 2007, 9:48 pm

ZERO air pressure on these forks, those air valves are to get rid of any built up pressure in the tubes. I also have a 1990 851, love it! What weight of oil are you running and how much are you putting in?

alwill923 · Oct 1st, 2007, 6:48 pm

thanks for the reply.

The shop manual or the 851 said 160 mm from the top and the Marzocchi book said 180 so we put the oil level to 170
The oil was 5 wt.
I think we put in 10 psi of air. We will not do that again.

weldingshop · Oct 1st, 2007, 6:57 pm

I read that the 851 had some strange handling issues.............have any opinions......never rode one, wanted one though.

Buckelew · Oct 1st, 2007, 6:58 pm

Quote:

Originally Posted by weldingshop

I read that the 851 had some strange handling issues.............have any opinions......never rode one, wanted one though.

strange handling issues.....like they're ROCK SOLID?

Desmo_Demon · Oct 2nd, 2007, 8:34 am

Quote:

Originally Posted by arw

The shop manual or the 851 said 160 mm from the top and the Marzocchi book said 180 so we put the oil level to 170
The oil was 5 wt. I think we put in 10 psi of air. We will not do that again.

I recently rebuilt the Marzocchi M1R forks on my '87 Paso 750 and used the Marzocchi rebuild manual as my guide. I filled mine at 180mm from the top and had zero psi after assembly. I don't know how well everything turned out, as I only have about 8 miles on them since the rebuild.