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Aprilia Forks - Again


canadianstrom
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hello all

I'm looking at improving my fork behaviour again. Last year I replaced seals and oil , put in 260 cc of 20wt as I saw recommended on this board. It was way too harsh , I couldn't ease a wheelie down without hand shock. I switched to ATF which is 10 wt ( ? ) better but still harsh. I have since seen a recommendation of 10-20 wt in the rebound fork and 5 wt in the compression side. This sounds like a good idea but I'm not sure which is which. Is the fork with the adjuster for rebound?

Also there is 2 allen screws on the top of the left fork , the one clicks so I assumed it is for adjusting rebound damping, clock wise ( ? )for more damping ( less spring back ) . I had assumed the little allen screw was to lock the adjuster screw bit itdoesn't seem to bottom out. any ideas?

thanks for any input.

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just to let everyone else know what I'm finially figuring out here. I aske Mike @ the tryals shop and here is his reply

"The fork with the adjustor of clicker is the damping side or compression side. Many misunderstand the forks. For most Trials bike set ups they only have a spring on one side and a damping cartridge on the other. The damping side controls both compression and rebound strokes so any adjustment of the clicker changes the feel. So you can regulate the speed of the travel but the adjustor changes it evenly on both strokes. As you have learned the oil viscosity also changes the speed of travel. The spring side doesn't do much except hold the front of the bike up and return the forks to the top of their stroke. The oil on that side makes little difference and only serves to keep the spring lubricated and cool.

The two screws on the left fork have separate functions. The one in the center or clicker adjust both compression and rebound so you can make it faster in both directions or slower in both directions. The other one is just a vent to relieve pressure if any builds up. You notice this if you forks should start feeling a little stiffer but you haven't changed anything. Just loosen the screw and you will here the pressure escape."

I went with 5 wt oil in the left fork , huge improvement. maybe could have went a little lighter yet.

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  • 3 weeks later...

hello,i to have had this problem,first put a heavey oil in and found that the forks were rock hard so i changed to 5wt and they are fine ,also can any one help me,i need a bigend bearing for my aprilia climber280 1990,if anyone knows were i can get one from i would rely appricate your help.

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Gday, look at the spring first! The spring does the work, and the damping slows it down. If your spring is too stiff no amount of fiddling with the damping (compression and rebound) will fix it. Get that right for your weight and riding style first, and then fine tune with damping. Also check there are no mechanical issues - bent fork tube etc.

Cheers,

Stork

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Stork

You made some good comments there. I kind of figured that the spring wasn't too stiff for me because before my initial oil change I could bottom out the forks. Now it the tubes show I'm not within an inch and a half of bottoming out (and still a little harsher than I'd like, as I movce through the stroke it feels good , kind of a abrupt stop at the end of the stroke I think is what I'm perceiving). Can I safely say that's due to the dampening effect? perhaps need to play more with the clicker, lighter oil or even less oil ?

The tubes look good, pushing down on the forks doesn't feel like much stickion, nice smooth movement.

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can any one help me,i need a bigend bearing for my aprilia climber280 1990,if anyone knows were i can get one from i would rely appricate your help.

Anthony

i'm noy sure which bearing you'r talking about. If you are in North America , Mike @ the tryals shop has had any parts I've needed and great to deal with and offer help and advice.

Wally

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Gday Wally, you can vary oil amount which will change "springing". More oil = less "springy", Less Oil = more spring. The Air space acts as a spring on its own, so if it feels too stiff, try adding a small amount more of oil. Careful you dont go too far as too much will cause hydraulic lock at a certain point, when there is no more space to use up for the oil. The best way to do it is to measure the height of the oil in the fork with the spring removed and the fork fully compressed. I assume the Aprilia has the Paoli's on it with the spring in one side and the damper in the other. Perhaps you would only need to adjust levels in the spring side, but it might be better to both the same just to be sure. I would think in an older bike that 5 weight would be as light as you would need, but I could be wrong...

Cheers,

Stork

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  • 1 month later...

just a further update to anyone interested.

I was still struggling with the front end, not absorbing little bumps and deflecting off small stuff. i measured the total stoke 19 cm , the static sag was only 1 cm (no rider) , sag with me on it was only 2or 3 cm. If I pushed down on the seat, only the rear suspension moved. I've read the rider sag should be 30 to 50 % of the total stroke for trials bike. I loosened the cap from the right fork tube ( spring side) and the static sag only increased by a cm or 2 so the damping side was doing a lot of the work to hold the bike up. I've tried letting the air out of the damping side via the small screw but no air ever came. I unscrewed the cap and a lot of air pressure was released and the bike gently dropped to bottom of the stroke. I pumped the cap up and down listening for the sound of air being moved thru the damper, no sound so I assumed the oil level was high enough. So with the forks still bottomed out I tightened the damping side cap to reduce the amount of air in the fork.

I've ridden the bike and It's much improved, better shock absorbing and easier to balance at stop or low speed ( i assume because the bike geometry is better with the rider sag at the 7 cm it is now. static sag is 4 cm . Pushing the seat down gets both forks and rear shock compressing although the front shows a fair bit of stiction.

It seems to me that the problem is air pressure building up in the left hand ( damping fork) and the air release screw is not working so if the forks get to stiff again I'll try to unplug the air release.

Stork, I'm not sure which shocks are my Apr,they are the upside down forks, gold outer tubes, aluminum caps and bottom of the fork tube.

In your post did you think the air pressure would be building on the spring side? is any of this making sense ? or am I just floundering here?

I welcome any feedback.

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Gday Wally, both forks will increase air pressure as they get hotter with use. It sounds like your front sag is better, but maybe a little high statically. That is not as important as feel however. Both ends of the bike should move pretty much together. It sounds to me that you need to play with the oil amount in both forks - the easiest way to do this is to use a syringe with a hose that you can calibrate the length and remove oil above a given height. These tools are available cheaply if you dont want to make one. Start from factory and vary from there. What the factory level is - ? I have no idea. Maybe someone will chime in with the spec. From there vary a few mm at a time, and remember that less oil = more springing, and more oil reduces springing. Have you experimented with the damper settings at extremes to get a feel for how it changes? That is also a good starting point and costs nothing. Finally, its best to only change one thing at a time so you can go back to where you started if you dont like the results. Use a note pad and work from there.

Good luck,

Cheers,

Stork

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