January 1, 201016 yr I have some 1971 Alpina forks and notice that the fork caps are vented so that they will breath in and out as the forks work. I have never seen caps like this. Would it make the fork more progressive if they were sealed..with maybe a valve to relieve pressure? Would it then blow seals?
January 2, 201016 yr Bultaco Betor forks were not the only 1970s forks to have vented caps. Yes non-vented caps can be used to tune the overall spring rate but beware because Bultaco Betors only have friction to retain the the fork seals so if the pressure goes too high you may cause a seal to pop out. I have been running a Sherpa T with non-vented caps and haven't had a problem yet, but that is no guarantee of anything
January 2, 201016 yr The Bulto valves would stick but are easily cleaned out. As for the caps with Schraeder valves you pays your money and you takes your choice - these have been advertised in different eras as improving fork sealing (1) due to allowing pressurisation with a pump thus forcing the seals against the stanchion and preventing oil passing and also (2) by allowing release of pressure build up which would force oil past the seals. Marketing man strikes again.
January 2, 201016 yr Feetupfun, there should be a circlip at the top of the fork leg after the 2nd seal, all the Bultaco forks I have stripped so far have had one.
January 2, 201016 yr I believe the Betor forks were meant to run vented on compression, possibly to create a partial vacuum. Only Betors I have seen unvented are in my mk9 Pursang. The fork cap with the diaphragm valve always seemed (to me) to give the most trouble. The ball and spring type are simpler and give no trouble. Wayne.....
January 2, 201016 yr Feetupfun, there should be a circlip at the top of the fork leg after the 2nd seal, all the Bultaco forks I have stripped so far have had one. Some have circlip grooves, and some don't.
January 5, 201016 yr The early Sherpas have non vented caps and cause no problems, the later vented caps can actually leak oil after a hard days riding resulting in many riders I know actually sealing up the vent, with no adverse effect. The action of the forks is the same. All my sherpas have a circlip holding the seal in place, I have never heard of anyone blowing a seal with either setup and Ive had sherpas since 1970
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