Motorcycle Repair: 1982 YZ 490, crankcase oil, oil mixture

Question
I have a 1982 YZ 490 that I need to change the "oil" in.  Had a carb overflow that spilled into the cylinder.  How do you drain the oil and know when it is full. And, what type of oil should I put back in it.  I just had the entire engine rebuilt and do not want to risk damage if gas got into the lower end.  Please talk to me like I am a little kid as I have not worked on this bike at all or any other for many years.

Thanks
John

Answer
John, There is a drain on the bottom of the engine to change the transmission oil.

http://www.cmsnl.com/yamaha-yz490j-competition-1982_model8899/partslist/B-02.htm...   #23

A two-stroke engine has separate transmission oil, partitioned from the actual crankcase where the fuel/oil mixture swirls around for transfer to the cylinder. This is a different scenario than a four stroke engine where gas can contaminate the crankcase oil.

If the carburetor did a major amount of spillage in the crankcases, then I would suggest a couple of ideas....

Remove the spark plug and exhaust system, make sure that the KILL switch is on OFF (or ground the spark plug lead) so you don't create any unwanted sparks in the presence of explosive gasoline mixtures, then kick the motor over about a dozen times to pump the excess fluids out of the cylinder and cases. If you really want to be sure it is all out, remove the fuel tank and just turn the bike upside down with the spark plug out and let it drain for an hour. Having the intake disconnected along with the exhaust pipe should allow for maximum drainage and evaporation.

The crankshaft area of the crankcase doesn't have anything in common with the transmission, other than a seal on the primary side. If in doubt, open the transmission filler cap and smell inside for any signs of gasoline. Change oil if you have any concerns. Checking the web, I see that Bel-Ray has a product called "gear saver" oil for 2 strokes, so you might want to check into that for the next transmission oil change.

I don't know the capacity of your transmission. You can either contact your dealer for the specifications or just measure what comes out and replace it with the same amount. Whoever your rebuilder is will know, as well.

Bill Silver