This is a 3.0 L Mercruiser I bought to play with in a 17' Stingray. The motor runs great and only has 370 hours. It is cracked externally on the exhaust side of the motor about 3 inches below the top of the block about 3 inches long. I ran the motor today for 30 minutes and no sign of internal problems.
Ken

if you grind a small groove in the crack you can fill it with marine tex or jb weld have done this in the past on older boats and works well

JOE
AMERICAN PERFORMANCE MARINE
[email protected]

Drill a hole on each end of the crack {Keeps it from growing}
Welding is best but...I have seen JB Weld last for years !

2 of the best ways to repair crack are as follows----
1st is to get a crack repair kit from a machine guy that uses break off plugs. The way it works is you drill a hole at the beginning of a crack. Tap this hole with the tap that comes with it (1/16 pipe), then insert the breakable plug into the hole (with locktite of some other sealer) and tighten it until it breaks off leaving a flush surface. Then you take a small pointed punch and punch on the side of the plug you just installed (going toward the crack) and repeat this process until you reach the end of the crack. THIS TAKES A LONG TIME TO DO, BUT IS A PERMANENT REPAIR AND IN MY EYES THE BEST REPAIR.
2nd is to get a air chisel with a pointed tip and basically air chisel the crack back shut and then apply JB weld to the surface. This repair works very well on areas where freeze cracks are, because they are stress cracks created when the block froze and shouldn't have any more stress in that location again. I have used this repair an several blocks over the years and have never had problems.