I have the owners manual and all that good stuff but it shows a rear diff for gearbox and says I have to pull the gearbox cover off now im new to atvs so is the gearbox the one the chain is connected to or is it the area containing the wet cluch and drive belt!? and if somebody could tell me how I can put gear oil in my gearbox I would be very greatful just finished rewireing the whole harness, new cdi, overhualed the engine, rebuilt the carb made my own custom intake cause the one it had when I got it was cracked replaced bearings/seals and customized the original tail light to leds got it running good purrs like a 150cc kitten. so once the gearbox has lube again I will finally be able to take her out and do some ridin and a lil bit of fishing. thankyou for you time have a good day. bye.

 

I also have an 08 hensim 150cc quad. I went looking for the fill plug quite a while ago. On most GY6 engines it is on the side of the engine and exposed. On mine I came to the conclusion that it was under an engine cover - I think under the CVT cover (it has been a long time). I never went any further looking for it.

The location of the fill plug is documented in the GY6 service manual. You say you have the "manual", but does that mean a typical worthless chinese owners manual or the full blown GY6 engine service manual? GY6 engine service manuals are (or at least were) downloadable for free.

Check this thread for links to GY6 service manuals that worked a while ago:

http://forums.atvconnection.com/chin...fo-needed.html

If worse come to worse you could always just flip the ATV upside down and pour the tranny oil back in through the drain plug. Seriously. Take the battery out first so it won't leak acid out the vent hose, and drain the gas tank. I've had my ATV upside down several times both on accident and on purpose. Once righted it starts right up with no problems. Get the gearbox volume info from the service manual so you put the right amount back in if you go this route.