Its time to change the final drive oil on your CH250. Yes, boys
and girls, it's a little time consuming and somewhat aggravating
to remove the body center cover, left side panel and rail, pillion
step and brake cables just to get to the left crankcase cover so
that you can access that little drain bolt but you have to. It's best
to do this while the bike is on its center stand.

The oil check bolt has a washer and is the larger of the bolts near the clutch
assembly. It's the one that the rubber hole cover exposes without
removing the crankcase cover.

Remove the oil check bolt. The oil should seep out some.
The oil drain bolt also has a washer and is the smaller bolt directly
under and to the left the oil check bolt.

Remove the oil drain bolt and drain oil in a pan until crankcase is
empty. To get all the oil out, replace the oil check bolt and apply
light compressed air through the crankcase breather tube which
runs outside the back of the crankcase to the air filter box.
Reinstall drain bolt. The Honda service manual recommends at
every 12K miles or two years whichever comes first you change
the oil and fill the crankcase with a good 10w30 oil through the
check bolt. Reinstall check bolt. Start engine and test ride for 2-3
minutes. Stop engine and check that the oil level is correct and
that there are no leaks. Reinstall left crankcase cover and body
parts in reverse order. And now the truth---You really want to use
a good 75w90 gear oil such as Mobile 1 synthetic in the final
drive. And, all giggles aside, change the oil at least every 5K
miles or two years. You're not fighting heat in the transmission
here but rather gear shearing. Buy the oil that best fits the
prevention. Randy Pozzi