The saying “Fools rush in where angels fear to tread” may apply to me, since this my first post to this excellent site.
It appears from the recent posts of dejohnson88 that the hole is below where the piston last stopped. I would suggest you make an effort to deburr the backside of the hole before you turn the engine. Although I would expect the piston to break off any burr, it’s possible that a burr could get wedged between the piston and cylinder wall causing a gouge in the piston or wall if the piston moves down past that level.
Most of the suggestions so far seem to have concentrated on filling the hole in some fashion. I don’t think filling the hole, with possible negative side effects such as material extending into the cylinder, is necessary. All that’s needed is to seal the hole to prevent leakage. I suggest that bonding a small steel disk or plate to the outside of the hole can do this, somewhat akin to patching an inner tube. (Steel and cast iron have similar thermal expansion properties so there would be negligible thermal stresses.) I would avoid welding the patch for at least two reasons. First, welding involves heating metal to the melting point and I cringe at the thought of heat-caused distortion in a cylinder that has rather tight tolerances. Second, the comments that handyman made convinced me that it is a difficult welding task. I have not used JB Weld, but the web site claims it is an epoxy resin that is waterproof, oil resistant, and good for up to 500 F. In this application it would be used as an adhesive. A disk or plate provides plenty of bonding area to hold any expected load as long as the bond covers up to the edge of the hole. (Since the hole is only 0.125 inches in diameter, even peak combustion pressure would result in a load less than 30 pounds force.) Actually, if the hole is through the water jacket into the cylinder below the piston ring travel then the real load will probably be water pressure, and that would be forcing the repair tighter against the hole. If the repair leaked, you should be no worse off than you are now. The repair can be checked at any time for deterioration by “carefully” removing the freeze plug. If you were going to sell the tractor you could tell or even show the prospective buyer.
dejohnson88, good luck on whatever fix you choose.