Mechanical question, what's that small hole on the cylinder head?

[MastaMax]

What's that small hole for? Johnny told me last week but I forgot.

I get some fluid leaking sometimes, wonder if it's bad?

 

[KTMphil]

Is it the drain hole for the recess/ cavity of where the spark plug is located in the cylinder head casting? If you submerge the bike deeper than the cyl. head in water, that recess fills up with water and the spark plug HT lead will short circuit against the cylinder head with the water being conductive.

 

[Davevb]

Hard to tell from the pic but they are sometimes used to bleed the coolant of air once you top it up after draining it. If it is threaded with a nut on it then thats what it will be or just what Phil said.

 

[MastaMax]

Talked with Johnny, it is as Phil said, drain from the spark plug recess.

Here is some more info I found if people wonder why rusty water leaks and how to avoid it:

this is from water going up the little hole in the right hand side of the cylinder head when you wash the bike. so stick something in the hole before washing. a golf tee works great. i always blast some wd40 into that hole after washing, just to be sure there is no moisture in there.

if you cross some high water that may get into the hole, don't forget to do the wd40 blast when you get back to the truck. although in this case the water is usually quickly boiled out from the heat -- which is yet another reason you should run your bike for 5 minutes or so after washing it.

if you are asking what that hole is for, you are probably the one millionth person to do so. it basically allows the spark plug recess to drain. so it works both ways, doesn't it? you can also pop the spark plug wire cap off if you blast compressed air into this hole using a rubber nozzle

Good thing I just ordered a new iridium spark plug. Will be cleaning that hole after washing/deep river crossings.