I'm chasing an oil leak on the lower passenger side of my engine (1979 corvette with a 350 SBC). I noticed there's this weird hole under the block where the fuel pump mounts. What is this for?

 

No use other than when the block was made. The likely source of the mystery oil leak is on the front of the block about 1-1/2 or 2" up from there. There should be a short 3/8 bolt plugging the hole. The purpose of the hole in the front of the block is to lock the fuel pump pushrod in place when changing the pump. If the bolt is left out it will leak oil. Just be aware the bolt is only about 1/2 inch long, if it's too long, it will lock the pushrod and stop the pump from pumping.

 

Hi m,
I see it appears to be a 'hole' with 2 diameters.
Perhaps it was used as part of properly indexing/locating the block for it's first machining processes?
Regards,
Alan

 

Unlikely. Castings were located using flat 'pads'. I suspect that is not a Corvette block and that machining was relevant to whatever Chevy product that block was made for.

Machining into a cast iron housing that close to oil supply can generate an oil leak. Castings are porous and can have gas pockets which provide for leak paths when cut into. Clean that area off WELL with grease cutter, then lacquer thinner. Then, put a piece of dry/clean paper toweling up into that bore and leave it overnight. In the morning, pull that towel out and inspect it for any oil seepage. If none, put it back in and drive the car for several miles. Sometimes the oil needs to be hot to get it to flow thru small leak paths. If still no oil, that is not your leak problem source.

 

Remove bolt, clean threads and block with brake cleaner, and use SEALER on the bolt threads...

 

Hi,
"Unlikely. Castings were located using flat 'pads'. I suspect that is not a Corvette block and that machining was relevant to whatever Chevy product that block was made for"

I'm sorry, but my answer was based on information from John Hinkley's multi-part article in 'Corvette Enthusiast', entitled: "Small Block Assembly Overview".
A hole in that location is pictured and described as being one of the 2 major gauge holes used to register the block on it's machining pallet. The other gauge hole is just inboard of the starter mounting location.
Regards,
Alan

 

Alan is correct as usual. Every sbc I have ever seen has that machined hole.

 

I thought that as well, and I didn't have a bolt in the hole so I plugged it, but I still have an oil leak (in fact it got even bigger today, left a much bigger puddle in the driveway). I'm thinking Oil pan gasket or fuel pump gasket. If I can't figure it out, I'll ad some more pictures in this thread tomorrow. Thanks for the help!

 

My error. Went to check mine and that 'registration' hole is there. Chevy apparently used a completely different process to qualify castings than many of the other divisions.

 

Believe it or not, there is a small hole on the fuel pump that will leak oil....check that out. The lower one pictured below.

 

You might also check the oil seal behind the harmonic balancer that's pressed into the timing chain cover. Mine leaked at that seal, and I replaced my fuel pump & gasket and pulled my hair out trying to find the source of the oil. As you drive, the air from the fan pushes the oil down the side of the block leading you to think it's coming from the fuel pump area. Good luck.
Duane