I knocked out the old oil galley plugs and tapped them for pipe plugs. This is on a 90's factory roller block with the 2 lower oil galley holes already at 9/16" so I had to tap these for 3/8 pipe plugs. The left one cracked right where a previous "stake" mark was put from the machine shop a few years ago. Do you think that the stake mark stressed this area and was already weak? I have never seen anything crack like this just from tapping threads. The main oil galley is still at 7/16" so I tapped that to accept a 1/4" pipe plug. I will try and get some pics up tomorrow. What is everyone's thoughts on this?

Could be the combination of the stake mark and the wrong size hole for the 3/8" npt.
Might have had better luck with the 37/64" hole that the 3/8" npt calls for.
Might be salvageable ,waiting for pics.

Yes I would say the stake mark is a pretty goood cause. Whena rod gets knicked or a place made in the metal from a foreign object. This is where they fail... Sorry for the crack, but its a late madel block and there plenty of them... Hope you can fix it though...

I didn't get a pic of my block yet, but I found another random pic of the front of the block just to show you guys where the crack is at. The red circle shows where the crack would be. The face of the oil galley (the part that is flat) is cracked and if you look inside the threads that i cut, they are cracked a little as well. The crack on the other side only goes down about 1/2", its not all the way to the back of the timing chain area. Do you think this crack can just be epoxied since it really won't see much stress?

Is it going to matter if it leaks oil ? Doesn't seem like it.

Won't matter much if it just leaks, but once a crack starts in cast iron, it usually continues to propagate; if that boss or plug fails, you'll have no oil pressure.

:beers:

Cracks scare me in engines. I'd either fix it by having it properly welded, or get a new block. Had one at the bottom of one of my bores years ago that was onl about 1/4" long. They found it when they magnafluxed it and said it might stay that way forever, or open up bigger. I decided to have it welded and when they heated it to stress relieve the block it split the engine in half.
I wasn't happy, but it was way better than if it had split open while running and scattered a new rebuild!

When parts crack, if not too critical of a location, the crack can/might be stopped by drilling a small hole at the end of the crack. How much cash invested in this block? Welding iron is not cheap or easy, last time I read about it.

For a basic run of the mill iron block it is not worth the time and money to have it welded. The process is difficult for the average welder and the nickel rods required are not cheap either. Most people that do weld blocks will not warranty the work.

An engine machinist and race engine builder who is a friend of mine, he said cracks in that area are more common than thought in that area when we found one on one of my engines. Its due to the nature that the tapered threads of the plug spread as the plug threads deeper. Because tha receiving thread boss is raised with little material on the side of the boss that cracks will occur when the theaded opening spreads due to the tapered plug. The good thing is the location of this problem. Because it is behind the timing cover, if a leak develops it will be small and the leak will drain right back into the crankcase.
If someone else has a different thought please chime in.

What about something like this (http://www.muggyweld.com/castiron.html)?

Anyone have any experience with it?

If the crack gets bigger you will loose oil pressure. How much,, I dont know.

Drill a small hole -.0625 or smaller- at the end of the crack to keep it from spreading and fill hole and crack with quick set JB weld. Be sure area is super clean before hand. This is not a high stress or load area like a cylinder bore, or bolt boss etc. Should be ok. Use a good sealer on threads on galley plug.