- Nov 8, 2003
How about a different topic for discussion. The cylinder valves have been with us since 98 when they were first introduced by Yamaha in their 46mm USD fork. They have been tried and abandoned by both Honda and Kawasaki yet still Yamaha persist with them. They allow oil to bleed out of the cartridge in a rather uncontrolled manner on both rebound and compression. This has resulted in less oil being pushed through both the rebound and the base valve. In order to compensate for the lower oil volume being pushed though the valves Yamaha has increased the overall stifness of the shimstack dramatically. This has resulted in a rather harsh feel, yet, on severe hits the fork still bottoms easily. In 04 model bikes Yamaha has dropped the elastomer bottom out in favour of the more conventional hydraulic unit. Was the elastomer system to blame? Or are Yamaha simply trying to save face for using the cylinder valve in the first place? To me the fault was not so much with the bottom out system. The fault was in the fact that the fork reached the bottom of the stroke in the first place. I mean if a car runs off the road and crashes through a brick wall. Do we blame the wall for being poorly constructed? To me I see little value in the cylinder valve and prefer to replace it completely. RaceTech have a cylinder valve seal which simply stops oil from passing through the valve. These seals worked fine when yamaha were using mild steel damper rods. But since the introduction of alloy rods in 2000 the added seal drag produced excessive stiction and we had a whole new range of problems to deal with. Here in Australia we have a cylinder valve replacement kit which consists of a billet alloy piece in the same shape and dimensions as the original unit. The difference is it contains only a simple shaft bushing, the same as other fork designs. This kit allows the fork to work as any other fork. The shimstack can be valved much lighter for a plusher, more controlled ride. Stiction is reduced and bottoming resistance is dramatically increased. I have yet to be convinced of the positives of the cylinder valve but I am willing to listen. Anyone...?