1953 cadillac 331 engine block question. "F" hole or "A" hole?

mooman929 · April 04, 2014, 01:50:27 PM

hello im rebuilding a 1953 331 Cadillac . on the back of the block by the distributor there is a threaded hole marked A or F. im pretty certain the oil pressure sensor goes in one. what do they mean? what hole do I use and what do I do with the hole I don't use? thanks!

mooman929 · April 04, 2014, 06:06:00 PM

anyone? please?

Quentin Hall · April 04, 2014, 06:32:24 PM

Yes the oil pressure switch does screw into the back of the block at about the curve of the breather pipe. The back of the block I am looking at is too dirty to determine an A or an F. The temp switch screws into the rear of the rh head.

mooman929 · April 04, 2014, 06:36:18 PM

the two holes are next to one another. I think A is on top of block and F is off to the side? is ur oil sensor straight up and down or angled towards the right side of the motor?

mooman929 · April 05, 2014, 11:27:02 AM

Here is a pic of what I'm talking about.

mooman929 · April 05, 2014, 01:19:40 PM

anyone?? pleasseee???

Dan LeBlanc · April 05, 2014, 01:51:43 PM

Ive had 5 61/62 390s and the sender was always in the a hole. The F hole was always plugged.

mooman929 · April 05, 2014, 02:59:32 PM

Ok thank you. I'm just confused on what they mean

txturbo · April 06, 2014, 10:10:45 PM

My 56 365 had the sender in the angled hole and a plug in the top hole. I added an oil pressure gauge to the top hole.

mooman929 · April 06, 2014, 10:12:03 PM

I wonder what the letters stand for?

Bob Hoffmann CLC#96 · April 06, 2014, 11:18:03 PM

Quote from: mooman929 on April 06, 2014, 10:12:03 PM
I wonder what the letters stand for?

Don't ask! LOL!

mooman929 · April 07, 2014, 06:38:52 AM

Anything labeled "A" hole or "F" hole can't be good..... lol

The Tassie Devil(le) · April 07, 2014, 08:07:06 AM

Looks like the hole marked "F" in your block is already plugged. This looks like a factory machining hole that is drilled as an oil passage to the internals, and then plugged with a welsh plug to seal it.

Bruce.

mooman929 · April 07, 2014, 08:10:13 AM

Its not plugged its just an open threaded hole

The Tassie Devil(le) · April 07, 2014, 08:21:24 AM

I see it now. One looks like it has been fully plugged in all the way with a screw bung, and the other only partially.

If you poke a piece of wire down one, can you see the wire passing the bottom of the other one?

If so, and it is for an Oil Pressure Sender Unit, then I would be putting the unit where it is easiest to get to, and is not in the way of other parts when assembled.

Bruce.

mooman929 · April 07, 2014, 08:31:19 AM

thanks. yeah im gonna put the sending unit in one and maybe run a pressure gauge off the other like txturbo mentioned

Dan LeBlanc · April 07, 2014, 10:39:55 AM

I've always been curious as to why they had the two ports. The best explanation I can come up with would be to diagnose an oil pressure light without removing the sender.

The Tassie Devil(le) · April 07, 2014, 08:34:01 PM

I believe the reason for the two ports was so that oil passages can be drilled to where they need to go during manufacture.

Lots of blocks from all manufacturers have blocked-off oil galleries. Plus, it is not only Blocks that have drilled and then plugged up orifices. Carbies have them as well.

Where it is impossible to get a drill in from one side, they go in from the other side.

Bruce.

Quentin Hall · April 08, 2014, 03:09:24 AM

Sorry missed this post last few days. Bob, you cracked me up. Just checked my 53 Block more carefully. A hole is blocked with a square headed plug. F hole is the one for the pressure switch. . . Q

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1953 cadillac 331 engine block question. "F" hole or "A" hole?