What's the hole for?

[Lucky]

No! not that hole... ::)
The one on the side of each head, just below the valve cover.  I know there's not supposed to be anything in there, but someone was asking me.  they say they can feel air movement (either in or out, depending on engine temp)
my (wild) guess is that it is for air expantion between the cooling cylinder and casting...
any ideas?

[Cdnlouie]

I am speculating here, but my off-hand thoughts about this hole is that it is a drain to keep water from building up around the spark plug and causing it to short out.  Could happen from a heavy rain or washing.  Air movement here could be from a loose spark plug or simply air convection (ie. stove pipe idea).

[Lucky]

I sold my spare heads to Steve, (may he use them in good health) so I don't have any off the bike to look at.  A drain for the plug? I don't remember the plug recess being that deep, besides, I think any water there would sizzle off, but you might be right

[james ransom]

     it was the only to blow air into the spark plug thread area, and you can remove stubborn caps with a 125lbs air pressure

[Lucky]

so if i pour water on the spark plug with the boot off it'll come out the hole? neat party trick!

[jasonm.]

Guys, Yes it is a drain to let the water gods out. My venture has the same design. Also spray some wd-40 or brake clean down from the top of the spark plug prior to removal. Thus washing crud out. That 125 psi idea is quite a reach...

[bikehandle]

Guys
I found out the hard way, my vision had been wrecked years ago and I found it in a guys back yard laying on its side in the grass and leaves. all the electrics were gone along with the sidecovers, the front end was mashed, it had layed there over three years but having had visions before it was a labor of love to restore it. the point of my story is after getting it all back together I took it to the car wash, ran fine going but damn neer didnt get it started to go home! when I got it back to the shop I noticed some water weeping from what I thought was a hole that had a plug in it. I had noticed it before and thought it was a casting hole into the water jacket. when I ?took a toothpick and cleaned it out, a quarter oz of water ran out from around the spark plug. the hole was pluged with leaves. :-[

[sdinino]

I'm a little late to the party, but yes, the holes are water drains.

Thanks for the heads, Lucky. The bike is running again, and no more coolant leaks from the head gaskets. I'm not sure if it was a bad gasket or a bad sealing surface on my old heads, but everything is fine now.

Now, if I could just find a backrest for the wife, I'd be all set for spring... :-)

[Lucky]

Hey Steve,   Humber came up with the perfect solution for not having a backrest: have her face the other way! :D  lol

[Silver_Bullet]

Man, Humber really left himself open for a Polish joke with that suggestion ;D.  At least the guy's got a logical wit!