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How to Free Stuck Nuts and Bolts on a Marine Engine. Hint: Use Fire and Ice

a Propane-Torch an aerosol can of CRC Freeze Off

Learn how to loosen stuck nuts and bolts corroded solid on a cylinder head and free stubbornly frozen stainless steel bolts in an aluminum lower unit.

Stuck Fasteners Are Constant Source Of Frustration For Do-It-Yourselfers. On marine engines, and outboard and stern drive lower units, the problem is compounded by corrosion accelerated by damp, salty air. Here are some solutions for fixing this perennial problem.

If you work on a boat you already know from experience nuts and bolts freeze in their threaded bores with frustrating frequency. Sometimes it's a carbon steel bolt corroded solid on a cylinder head. Other times it's a stainless steel bolt frozen solid in an aluminum lower unit. Trust me. The only way to break it loose is with patience, bloody patience. Count to ten. Swallow the frustration. Then, one by one, follow the timeworn remedies revealed below that have been passed on from the dawning of the Iron Age. Next time a nut or bolt won't budge, don't make the mistake of losing your temper. Instead, heat it, or freeze it.

Don't make the rookie mistake of trying to free a stuck bolt with brute force, especially a fastener stuck in an aluminum housing. Otherwise it may snap off further complicating matters. It's a better strategy to walk away form a job for a day or two than risk making the situation worse. Besides, it's almost karmic the way coming back to a job after even a short break seems to make things go more smoothly.

Begin with fire. An oxy-acetylene torch works best. The downside is cost, if you don't already own one, they are expensive to rent and complex to fire up. And because of the inherent danger of working with an open flame near an inboard gasoline engine tucked into an enclosed space, first run the bilge blower for several minutes to ventilate the area. Wear leather gloves to protect your fingers from burns. Usually a couple of minutes of flame from a propane torch is sufficient. This method works because heat expands the metal, breaking its threads loose from the rust that's locked it in place.

Know that sometimes the flame blossoming from the common propane torch may not hold enough BTUs to get the job done. Either way, oxy or propane, heat the bolt. No need to go red-hot, but hot enough so droplets of water flicked onto the bolt sizzle off into a vapor.

Let the bolt cool completely. On a hot summer day that may mean a wait of at least an hour. Contrary to popular opinion, it isn't heat expansion that breaks the fastener loose. But rather the repeated expanding and contracting of the hot and cold cycles that breaks corrosion's grip on the threads. One, twice, even three applications of heat may be required. Like we said in the beginning, patience is a virtue. It also helps to tap-tap-tap the stuck bolt with a ball pein hammer. Notice I didn't say beat on it. The tap-tap-taping vibration loosens the rust. And you should also know the rust along the shank resists removal more than does the rust on the threads. So keep placement of the tip of the flame in mind when heating a stuck bolt.

An alternative to fire is ice. Some mechanics claim dry ice will shrink a bolt enough to break corrosion's hold. Though most of us choose a torch because it's quicker if not more dramatic. Besides dry ice, there is another cool option. It is an aerosol spray that freezes metal ice cold, more particularly a blast of freeze spray, an aerosol that super chills metal parts to minus 72 degrees Fahrenheit. The exact opposite of heat, deep-freezing metal contracts the fastener, breaking the tension between the threads and the rust. This time the strategy is to wait for it to warm up to room temperature before giving it another blast of cold air. In extreme cases, alternately heating and freezing will do the trick.

Some DIYers use a candle, or beeswax, and a cigarette lighter to free stuck nuts and bolts. By this method locate the lighter on one side of the fastener and heat it for a minute or so. Then light the candle and drip hot wax onto the threads. Old timers claim this works most of the time.

a Broken-Bolt-Extractor

broken bolt extractor

Sometimes the corners of bolt head round off making it impossible for a wrench or socket to grasp hold. Purely mechanical methods are also effective. Sometimes. Extractors are useful when the bolt head has been rounded-off leaving nothing for a wrench or socket to grip hold of. The most common method is to drill a hole in the bolt head, from the top down, a bored tunnel inside the bolt, paralleling the threaded shank. That done, thread an extractor bit into the hole until it bottoms out. In effect the bit becomes a new bolt head, one you can really grab hold of. Because its threads are left hand, cranking counter clockwise on the extractor grips the bolt tighter and tighter.

Depending on what parts the bolt holds together, consider drilling a rescue shaft at an angle in order to reach deep in the threads. The drilled hole is a rescue shaft of sorts, one that lends direct access to the corroded threads allowing them to be soaked with penetrating oil, coca cola or any other concoction you have faith in. Obviously this method is not available where drilling would destroy the very parts you're trying to remove.

Stanley Ball Pein Hammer

Never use force. Just get a bigger hammer.

Another method, relies on a center punch and a ball pein hammer. Pein the distressed bolt head, expanding the metal outward, forming new corners into the approximate shape of the six-point star, a profile a wrench can grab hold of. As a last resort, when willing to sacrifice the bolt, position the wedge tip of a cold chisel against the corner of the bolt head or nut and bang away with repetitive strikes of a ball pein hammer. Strike the chisel so the impact forces the bolt head counter clockwise, loosening it. Wear leather gloves to protect your hands.

Reassemble With Grease
Gasket Sealant for protection

Triple-Guard-Grease Permatex Aviation Gasket Sealant

Finally, re-assembling fasteners with anti-seize compound may not be the best solution to the corrosion problem. This for the simple reason anti-seize paste and even grease contain microscopic bits of metal (aluminum and copper). Exposing dissimilar metals with an electrolyte, the water your drive is submerged in, induces galvanic corrosion. Marine grade grease is a smart alternative. Johnson / Evinrude dealers stock Triple Guard. Mercury's version, Triple Guard, is saltwater rated, and famous for the way it stubbornly sticks to an object without washing off. It lubricates without separating or hardening over time. Water pump housing bolts and gearcase bolts smeared liberally with Triple Guard are easily removed easily after years immersed in saltwater. Regardless of brand, the best product to prevent bolts from seizing in an underwater application is a waterproof grease. Not anti-seize, unless it is a non-metallic formulation. That said, some old-timer, factory-trained, OMC mechanics used to rely on Permatex Aviation Form-A-Gasket Sealant Liquid. The brown, gooey liquid in can with a brush in its lid. The sealer drys just enough to protect the threads, yet gooey enough to unscrew the bolt when it's time to be removed.