Hi! I need some advice. I'm about to change the front fork oil and seals (one of them leaks a bit and the oil has never been changed yet) The workshop manual recommends 5W synthetic. So I bought 2l of Motul factory line 5W. But digging some more into it revealed that the recommended Castrol 5W has a viscosity of 28 mm2/s thus the Motul I bought is around 18 mm2/s. What do you suggest? Should I use it anyway or try to chage it to some more heavy oil the same motul in 7.5W manybe? The bike is a 2011 SM 630 with 16000ish km on the clock. And I am light as a feather - 60kg (132 lb) without gear. Thanks!
I have Motul 5w in my softer re-valved SM610 forks, but might change to 7.5w because ive only got one click left before my compression is fully closed. The springs carry yours and the bikes weight and they are what should be changed to suit. If you cant find the feeling you need within the available adjustment range, then the shim stacks, air gap or oil viscosity are changed to suit how you like your bike to handle and react, the air gap kind of acts like an extra spring when the fork gets to the bottom of it travel. Heavy oil, a stiff shim stack or a combination of both will give a harsh, jarring feeling when riding, light oil, a more flexible shim stack or a combination of both will give a pogo stick like feeling, like having a blown seal. The further away from ideal settings, the more these characteristics will show. If you want to find out what your forks are doing, put a cable tie around the bottom of your right fork, then you can see how much travel you are using. Tell the forum how your forks feel and how you want them to feel, then we will be able to give better advice.
I'm pretty much satisfied with it as is. I'm using it at the stock 12 clicks setting and basically want the same feeling. Thats why I dont want to alter the viscosity of the oil that much. The other question is it possible to compensate that difference in oil with adjusting the compression? Dont be surprised if I ask something stupid. I'm a noob when it comes to forks and suspension.
Have your forks got the compression adjusters in the bottom? If they havent youve only got rebound adjustment and would be better staying with the same viscosity oil for the same feel. I got some basic but good instructions about suspension from an Aprilia tech back about 09 and learned more by adjusting and stripping my own forks. A forum is a good place to ask and to find out about these things
Yeah, sorry it has only rebound. The guy I bought the oil from is a really nice guy and will trade back the oil to the same motul but 7,5W weight. So I will use that just to be safe. Thanks for the help!
