early 348 heads fix

[oil4kids]

this GM photo suggests that you drill a small hole in early W heads for the spark plug cooling passages for later blocks. Now I thought there was not enough material on the head to do this.

[Bungy]

I think they are just refering to service replacement heads. Not the original 58 heads.

[threeimpalas]

I think they mean to drill the 1/4 holes in the block which match up with the holes in the '59+ heads when used as service items on '58 engines. There should be more information in the service bulletin than the pictures posted.

[Southtowns27]

You can't drill holes in the block...well, not mine anyway. I have a Dec 1957 block and it doesn't even have the bosses on the deck for the extra water jackets

[348NUT]

Read it again. It is saying that the replacement heads are just marked with drill spots( not holes) Don't drill the holes for use on the old blocks, drill holes in the heads for use on newer blocks.
What I find interesting is that it sounds like it was just done to make the spark plugs last longer. I know Aubrey for one has run these old stlye block/heads with no problems. I have a May 7th cast block that has the bosses for the cooling holes but the block is not drilled! It had the later style heads also with holes. Must have run out of drill bits that day?:p NUT

Thanks Mark for sharing.