chevy 350 thread

[DAXJOHN]

Afternoon Gents

Just writing too ask if you can advise on a thread size on a 1991 350 Chevy block.

In the oil filter area their is a 1/4" NPT thread for the oil pressure switch & gauge & just too the right their
is a coarse thread which I need too plug, can you advise what size is it.

Plus their is another similar thread on the same side, middle top edge of block & it plugs the water jacket, what size is this, probably the same.

Any help would be great

Best Regards
John

[trularin]

Isn't that a 3/8 NPT??

[vettestr]

John,
Near the oil filter boss is a 1/4 NPT hole that you know is for oil gauge or a pressure sending unit. Just above that is a 3/8 x 18 hole for the clutch fork ball. You do not need to block this blind hole if not used.
Just above the oil pan rail in about the center of the length of the block on each side is a 1/4 NPT hole that enters into the coolant cavity. I place petcocks for draining block on each side, agian they are 1/4 pipe thread. On the head deck area to the rear of # 7 cyl is a 1/4 pipe thread hole you need to plug after plug inserted in oil galley and before head is installed. Many blocks also have another oil galley port on the back of the block near the bellhousing mount surface, not inside bellhousing or behind flywheel but on thin area of rear of block. This is to the rear of the distrib. mount location.
Hope this helps you. Jeff C

[DAXJOHN]

Hi Jeff

thanks for the help, I will try too take a picture tomorrow & post it on here as it sounds different.

Regards
John