totalshell Posted September 11, 2006 Report Share Posted September 11, 2006 (edited) i've a pair of conventional forks on my montesa twin shock that are fantastic smooth and smooth as can be , they hold the bike straight over the roughest of rock piles the only downside is.. when they extend fully ( eg front goes light or heaven forbid the wheel leaves the ground) they give a clear 'clunk' as they reach full extension they seem to be ok when i took them apart and both legs do the same thing they have 10wt oil in at the minute whats wrong and how do i cure it.. Edited September 12, 2006 by totalshell Quote Link to comment Share on other sites More sharing options...
barrybaines Posted September 11, 2006 Report Share Posted September 11, 2006 I beleive there should be some form of plastic bushing in there too stop them topping out, maybe they are worn? (all this is dependant on the make of fork etc etc but thats all I can think of) Quote Link to comment Share on other sites More sharing options...
feetupfun Posted September 12, 2006 Report Share Posted September 12, 2006 Twinshock era trials forks usually have "topping" springs that compress just as the forks top out. It is possible to overwhelm these springs by using a lot of preload on the main springs in combination with light oil. Another possible cause may be insufficient oil ie the oil level goes below the damping holes on full extension. The plastic bushes you should find in your monty forks are "bottoming" cones which generate a greatly increased compression damping rate as the forks reach full compression. Quote Link to comment Share on other sites More sharing options...
woody Posted September 12, 2006 Report Share Posted September 12, 2006 Easiest starting point is the oil quantity as you probably haven't enough in each leg and the effect is more obvious when on rebound than compression. Quantity required obviously depends on the model and/or forks you have fitted. 10 weight is plenty thick enough. Try around 180cc per leg which is a sort of baseline for Ossa MAR/Bults and subtract or add 10cc increments until you get the result you want, although over 200cc on old style telescos/betors is probably too much and you'll lose travel through hydraulic locking. Later t/s Monts had Marzzochi style forks, not sure what the quantity in those is. Quote Link to comment Share on other sites More sharing options...
totalshell Posted September 16, 2006 Author Report Share Posted September 16, 2006 had the things apart today , really easy job considering. the allen screw in the base of the slider holds the damper rod. with the main spring out a piece of plastic tube down the slider held the damper rod while i loosened the allen screw the circlip at the base of the stantion came off easy and let the damper rod slide out easily the damper rod has a plastic 'piston' at the top and this is restricted on 'topping out ' by a spring similaer in apperance to and as strong as a 'valve spring' and seemed way too hard almost solid, as you'd expect from an engine valve spring, so i have changed it for a spring from a mountain bike fork and added an extra 20mil of oil i'll test them on thursday hopefully.. Quote Link to comment Share on other sites More sharing options...
totalshell Posted September 23, 2006 Author Report Share Posted September 23, 2006 i now know more about forks and springs than a springy thing.. the fork 'clunked' when 'topping out' out because the rebound spring was too stiff ( almost a valve spring) so that it provided virtually zero movement/ resistance to the main spring after measuring it all up i've ordered so softer and longer springs to experiment with in the hope that they will compress and slow the fork when it tops out , luckly i kept one fork leg as standard because changing the rebound spring to a softer one albe it slightly longer actually shortened the fork leg, once resolved fully i'll release all details to the waiting world.. Quote Link to comment Share on other sites More sharing options...
gasgas Posted September 24, 2006 Report Share Posted September 24, 2006 ttlshell, very cool how you resolved yr problem with the fork. Keep it in mind. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.