Hole in the Head

[48mirage]

I picked up a late P25 head to mill and instal on my D30 block. I noticed in the combustion chamber of #6 cylinder is a small hole, about .7 mm in diameter (mechanical pencil lead). This appears to be in the centerline of the block. On the top side of the block is a small screwed plug. When I remove the plug I don't see the hole (not to say it isn't full of crud, haven't cleaned it yet)

Is this designed into the head or did I just have head that developed a leak?

If it is designed, what was it's purpose?

[Plymouthy Adams]

It is of a purpose..this is for locating top dead center..and you can measure the stroke of your block in this fashion...when the plug is removed, you should be able to see right through..appears it is carboned up...

[martybose]

It's there so that you can find top dead center using a piece of welding rod, or something similar. Cylinders 1 & 6 go up and down together, but have the ignition cycles 360 degrees apart.

Marty

[T.Tom Meshingear]

A picture is worth 1000 words.

T. Tom

[48mirage]

Thanks to all. This shows the geniuses of days gone by. Simple solutions are always the best.