A head bolt should come out. Manifold studs are sometimes pretty tough. Be patient. Overnight is sometimes not enough. Give it more time. You might try the added heat from a propane torch - nothing too hot. If it breaks, drill small and hopefully drill through it so oil can work from the back. Then increase the hole size until you're almost to threads. Perhaps it will "easy-out." If not, you might have to grind it out with a Dremel. Of course, if it breaks, you could always check the cost of having a machine shop remove it.
Heat it up as hot as you can get it and touch the stud and surrounding area with a piece of wax or a candle. The heat will draw the wax into the threads and provide some lubrication to the stud when your unscrewing it.
A forum community dedicated to snowmobile owners and enthusiasts. Come join the discussion about performance, troubleshooting, trails, maintenance, riding tips, modifications, classifieds, accessories, and more!