Permatex Blue Threadlocker. Medium/high strength threadlocker for general-purpose applications. Especially well-suited for 1/4"to 3/4"(6mm to 20mm) fasteners that have a slight oil film. Prevents vibration loosening. Oil resistant. Removable with hand tools for easy disassembly. - See more at: http://www.permatex.com/products-2/product-categories/thread-compounds/threadlockers/permatex-surface-insensitive-threadlocker-blue-detail#sthash.swWRj5gX.dpuf
You may also need a lubricant while re-assembling to keep from damaging the parts, and in addition for high heat applications, use this anti-sieze compound, you'll be glad you did.