Saturday, October 26, 2013
Tips on Loosening Exhaust Head Nuts
The nuts that hold exhaust heads -- called manifolds -- onto the top end of the engine are prone to rusting and seizing. They are subject to extremely high temperatures, typically are made of a base metal and must be torqued down to extreme tensions to maintain their seals under operation. These reasons contribute to their being the bane of many a mechanics day. That said, a number of tricks can be effective in freeing the exhaust heads.
Safety
Exerting great pressure on long levers and working with naked flames can be hazardous. Wear protective gloves that save your knuckles if the bolt end unexpectedly snaps off, and keep your sleeves away from the heat source.
Patience
When stubborn nuts are encountered, it seldom is advantageous to crank them with increasingly long levers and short tempers in the hope they will give. The likely result is that the nut shatters or the stem of the bolt breaks off inside the manifold or head, creating many other problems. First try tapping the nut, sharply but not with such force that the bolt could bend; this often is sufficient to break the rust bond. If this fails, move on to other options.
Lubrication
The light lubricating oil ubiquitous in the tool kits and garages of the U.S. is not a penetrating oil, and probably is ineffective on a seized manifold nut. Numerous variations on the theme of penetrating oils are available on the market, and to a greater or lesser extent, all have some effect on a locked-up exhaust head bolt. Spraying penetrating oil onto the bolts and leaving them for the time recommended by the oils manufacturer may not work every time, but this easiest solution is worth trying before any more complex and potentially dangerous methods.
Remove as much rust as possible with a brush or scraper, then spray the exposed threads. Wait the advised time, then work both backward and forward with your socket; tightening as well as loosening works the oil into the threads. Frequently reapply the penetrating oil throughout the process. If time permits, spray a little more oil on and try working the socket every day for several days; this often works even if the first attempt did not.
Heat
Naked flame must be used with great care. The oil and fuel in the engine is flammable and explosive, as is the penetrating oil; aluminum cylinder heads can warp in a heartbeat if the heat transfers to them from the iron nut-bolt assembly. Rubber pipes, vacuum hoses and wiring must be protected. Use an oxy-acetylene torch rather than propane; the nut must heat and swiftly expand before the bolt heats and expands sufficiently to break the rust bond. Have an assistant standing close by.
Heat the nut to a cherry red, then pass the torch to your assistant and -- as quickly as possible but not so quickly as to cause an injury -- get the socket on the nut and, as before, exert pressure in both directions. Once the seize is broken, allow the nut to cool to the point where it is no longer glowing, then apply penetrating oil and finish off using that method.
