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CHANGE FORK OIL
Yamaha recommends using 10W30 motor oil or 10W fork oil. Motor oils can vary in actual
viscosity and are not "calibrated" to be exactly 10W and do not contain any components to "swell"
the seals. A good quality fork oil will provide much better performance and less weeping over
time, so spring a few extra bucks for the quart of fork oil rather than the 10W30 motor oil. Some
folks use automatic transmission fluid, but again, this oil is not designed for use in forks, so I do
recommend using fork oil.
Fork oil is a neglected item probably because most people just don’t understand how important,
or how much abuse, it takes. The oil picks up grit from the fork tubes and from material sluffing off
the fork tubes and legs. Since the lower housings are aluminum, it is critical to maintain clean oil
to avoid excessive wear. Also, very small amounts of oil are left behind on the fork tubes as the
seals work up and down during normal use, so the oil is actually consumed very slowly as you
ride.
To change fork oil, put a pan under the drain screw on the side of the fork leg. Take out the screw
and while holding the front brake, push down on the front forks. This will push out the oil. After all
the oil is out, replace the screw. Repeat for the opposite side. Check a shop or owner’s manual
and use a baby bottle or measuring cup to get the correct amount of oil. Remove the fork tube
caps and SLOWLY pour the oil into the tube. I say slowly because if you get in a hurry, the leg
will trap air and overflow. Then you will have to wait for the oil to run down and drain it out of the
leg, then start over. (I speak with experience!) Once all the oil is in the tube, replace the cap.
CHANGE BRAKE FLUID
Another neglected item that will cause problems if not changed is brake fluid. Brake fluid collects
moisture, no matter how tightly the system is sealed, and this corrodes brake parts from the
inside.
At the very least, brake fluid should be drained from the system and refilled with DOT 3 or 4 every
other year. A bit of pain, because the system has to be bled again, but it will pay off with reduced
maintenance over time.
If you don’t want to mess with this process - thoroughly clean out the system so all old fluid is
gone and replace with DOT 5 fluid. DOT 5 brake fluid is silicone based and will not attract water
like DOT 3 or 4. It will also not attack paint so you don’t have to be as careful with it. Just
remember that you CANNOT mix the DOT 3/4 and DOT 5 types of fluid. DOT 5 does not work
well with some rubber compounds, but I have not had any reports of any problems with Yamaha
components. The factory used the right compound so you will not have a problem with them. If
you have aftermarket seals, you could try soaking one in DOT 5 to see what happens.
CHANGE ENGINE OIL
Yamaha recommended 20W40 oil in all the 650 twins above 32° F and 10W30 below 32° F.
There has been a lot of discussion about which viscosity and type of oil is the best to use, but I
recommend 15W50 synthetic. I have recently changed to synthetic oil in all my bikes because
the zinc and phosphorous has been reduced in SG and SH oils. The 650 was designed to
operate with SD and SE oils. SF was much better oil but recent changes have made automotive
oil less suited for air cooled motorcycle engines. I don’t have access to a reasonably priced
motorcycle oil, so I use full synthetic automotive.
If you plan on keeping your 650, use a good quality 20W40 or 20W50 that is suitable for
motorcycle engines. Either petroleum based or synthetic is debatable, so you just have to take
