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Hello lokeypod.
You may have already seen this, but just in case, here is Don Moyer's answer to a FAQ about installing core plugs:
FAQ’s: Cooling
Freeze-out plugs were originally installed over a small ridge cast into the lower part of the hole in the block, head or manifold. Here are your options for repair, starting with the least invasive and leading to the more complicated procedures:
1) If the plug has some dome shape remaining, you could take a flat punch (like maybe a 1/2″ bolt) and flatten the plug. These plugs are designed to seal around their OD by flattening out their dome shape. Flatten the plug by pounding in a circular pattern around the center, but not directly in the center. The challenge is to flatten the plug without causing a concave dimple in the center, which would reduce the ultimate outward expansion of the plug.
2) If the plug is already flat, you may be able to seal it using epoxy of the type West Marine sells in small repair kits. Before using epoxy, be sure to clean the surface of the head and plug extremely well.
3) You can replace the plug with a new one from our online catalog (Product
number: OBLK_14_125) and reseal around its circumference during installation. Old plugs can be removed by drilling a small hole in their center and then inserting a punch and prying the cup out by pounding on the side of the punch. Since the inner circumference of the hole will probably be less than perfect, we recommend the use of JB Weld to seal the new plug. Flatten the new plug as in the first option above.
4) If, after removing the old plug, you discover that the ridge in the casting is deteriorated to the point that it will not support the pounding it will take to seat a new dome shaped plug, you can ream the hole to a slightly larger size and install a “cup” type plug. In our own rebuilding work, we routinely ream holes for the larger plugs (used in the block and head) to 1-1/4″, and to 15/16″ for the smaller plugs (two used in the manifold and one in the head).
5) For on-boat repairs, where poor access prevents repairs involving reaming etc., there are rubber expansion plugs available from many automotive parts stores which may work to seal a hole (at least on a temporary basis) that is too deteriorated to accept a dome type plug without the need to ream the hole. – Updated: December 22, 2003
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