Help - What is this hole for?

I recently purchased a 1998 WR400F that had low compression. The bike already had the tank, plastic, and carburetor removed. I removed the head and cylinder to find a stuck ring. I am in the process of putting it back together when I noticed a hole on the right side of the head centered just above the combustion chamber surface. Here is the picture. Any ideas on what it is for?


This allows the spark plug recess to drain

Yep. Make sure it's clear while you have it easy to get to.

Yup! It's just so you can blow air in there before removing the sparkplug to keep any debris from finding it's way into the combustion chamber. Maniac

Thanks for the help guys!!!

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