3rd Nipple
 

Hey
I just realized that my new 4 stroke(my 1st) engine has a 3rd nipple i the bottom. What Do I do w/this? What is it for? The documentation that came with it says that I should leave this open.

3rd Nipple
 

The '3rd nipple' is a crankcase breather. It doesn't really matter what you do with it, but it's a good idea to run a tube from it outside the cowl or away from the 'plane, to try to keep it cleaner.

Just in case you are wondering, the reason a 2 stroke doesn't have a breather is because the crankcase pressure is used to blow the fuel / air mixture through the porting into the cylinder as the piston moves up and down, whereas in a 4 stroke, the crankcase doesn't taking part in this function at all, that job being done by the inlet valve in the top of the cylinder.

Hope that helps!

David C.

3rd Nipple
 

When I saw this post topic, I thought you had to see a doctor or something...

3rd Nipple
 

The third nipple is also about the only way to get after run oil into the engine in the place it should go (crankshaft bearings) as you cannot put it in the carb and have it get to where it has to go to do any good. If you use after run oil (and it is recommended by most people) squirt about a teaspoon full into the crankcase and then turn the engine over by hand with prop shaft pointing down to thouroughly displace any fuel residue from the bearings.