Hi Richard, there are several methods to remove zincs from their plugs: 1. I center punch, then drill out the broken off threads with succeeding larger sizes of drills, then chase the threads with the correct size tap. If you use left hand drills, available in a kit of four from Harbor Freight, the broken off threads often back out as they are being drilled. Must be careful not to drill into the threads. 2. Put the plug in acid until the acid eats away the zinc. Caution: Leaving the acid in an open container will allow the fumes to escape, causing near-by bare steel to form a superficial coat of rust. 3. Drill an appropriate size hole and use a screw extractor. When this topic came up a few months ago, I'm pretty sure that I had read a few other ideas. Hopefully, others will add to this list. When replacing your heat exchanger, there are several manufacturers in the US that builds them. Most are available on the internet-googling heat exchangers. Just about all of them have the OEM plans for heat exchangers for just about any engine. When purchasing from one of them, you can change any of the specs to meet your situation. For example: Last heat exchanger I ordered for my engine, I had them change a couple of the size of the inlets and outlets to better match the hose sizes that the engine was designed for. For your use, maybe having them replace the OEM specs for the zinc with US specs. If there is enough room in the exchanger, maybe also have them size the threads for a larger plug. *Rudy & Jill Sechez * *BRINEY BUG-a 34' Sail-Assisted Trawler * *850-832-7748 * *Annapolis MD Chesapeake* > >