Hey i just got my 400ex about a month ago and i read the manual part where it says what oil to use. It says to use 10w 40 and it didn't say anything about synthetics. Can i use any regular 10w 40 motor oil?

 

Yes, but conventional oil tends to break down quicker in the 400, due to the high heat. I ran Mobil 1 15w50 in the summer time and Honda HP 10w40 in the winter months.

 

There has been many topics on this issue. Do some searches under "400ex Oil". Another good source of information for searches can come from:Exriders.

Try to avoid regular oils that have the "Energy Conserving" label. These are generally 10W-30 and lighter. These have friction modifiers in them that can cause damage and slippage to your clutch. Someone is going to chime in hear and say that the guy at their dealer said you have to use motorcycle oil or you will have clutch damage. As long as the oil doesn't not say "Energy Conserving", it will be fine. As for regular or synthetic, I am a big proponent of sythetic oil in atv engines. My 400ex came from the factory with petroleum based 10W40. The oil had broken down in less than 10 hours (break in period) and the machine was already burning oil. I switched to Mobil 1 15W50 (synthetic auto oil) and it doesn't use a drop anymore. I have 1 1/2 on the machine under some hard riding and no clutch problems whatsoever. Besides, you can get Mobil 1 from your local auto parts store for around $4 per quart. If you want to use a motorcycle oil, I would recommend Amsoil 20W50 motorcycle oil. The 20W50 synthetic will not break down like the petro based 10W40 will and will still flow well when cold. Hope all of this helps.