Went racing last weekend. Lost 2nd round -.003 red so I got back to the trailer and was going to drain the water because they're calling for low 30's at night this week and I don't want to crack the block. I took the radiator cap off and I notice the radiator is low. I look around and everything looks dry externally so I pull the dipstick and the oil looks milky. I started checking it out and I found water in #5 cylinder when I removed the spark plugs but it was also pushing out of the oil pan drain hole when I pressurized the cooling system. Suspecting a head gasket problem or a cracked cylinder wall I pulled the head off. The gasket looked good so I checked the cylinder. There was rust in the cylinder so I wiped it with WD-40 and started looking. I saw what looked like pitting so I took a pick and most of the spots were just spots then I found a pinhole in the side of the cylinder. I'm going to pull the engine this weekend and hopefully get it disassembled and pop the freeze plugs out so I can look for other possible problems. I assume it rusted from the back side of the cylinder so I don't know how much I'll be able to see. I will probably have it sonic tested and them hopefully I can just have it sleeved so I don't need to have another block completely done. I've never seen or heard of this happening. I wanted to let others know what I found and I was wondering if anyone else has experienced this before?

The guys that do my work have a 429 Ford in the shop now with the same problem, a sleeve took care of it.

The thing is if you have one hole thin with rust the others are probably in the same condition or not far behind.

Sonic test before you sleeve it.

If the rest of the bores are ok then sleeve away.

If you can sleeve it after the sonic test ask the machine shop your going to use what procedure they use for installing sleeves If they use a .002 or larger press fit you may need to have all the adjacent cylinders on that side sleeved due to permanent cylinder wall distortion causing the rings to not seal. if they use less than .002 and freeze the sleeves and warm up the cylinder enough so the cold sleeve will push in by hand you may not need to bore or sleeve all that side
How much is that block bored out to now?
In the future I would recommend using a anti rust additive in the cooling system

Ive seen this too. The back sides of the cylinders look like moonscapes on a lot of these engines from that era. Some are okay though. A sonic check might not hit or pick up the crater spot that might create the pin hole.

Most likely, all the cylinders may be in the same rusty/moonscape conditions on the Backside, or it could only be just that cylinder is really bad, or had a really bad spot.

But that one pinhole, would be a( cross the finger moment), that it would/could be the only bad spot lurking on all of the cylinders.

Once you get it tore down make a plate to simulate
the head but no holes except the bolt holes.. then
pressurize
the block to like 50 psi and see what you have from
the bottom side... if you can... add some heat... I
have a plate I made up for a SB(some where
around here)remember that each bank is separate so you
have to do both sides... add the air pressure at the
water pump holes

It happens more than you think ...

What year is the block , a sonic check might scare you , especially at the bottom of the bores ...