Im cleaning my 12A irons (83) and i noticed on the lower right side of the front side housing, there is what looks like a drain plug that goes into the water jacket. it isnt a regular bolt, it has no head, just a threaded piece, with an indent for an allen wrench. anyone know what this is for?

 

pics

 

Is it hard to get to due to the beehive's metal line? If so, don't worry about it. Some engines (R5 13B for example) had a water temp sender there.

 

I have also seen that same spot used for a block heater....

Dan