Restoration Tips for Antique Stationary Engines
Freeing Up Stuck Pistons
One questions asked the most in engine restoration is “how do I free a stuck pison?”. Many chat lines buzz with this question which is usually asked atleast once per month. A quick view of the archives in venues such as SmokStak, one can see the constant repeatability with which this question is asked. Ultimately there is on one good answer to this, although each person swears by his own method. There are a whole lot of tricks that one may try to reach their goal, but more often than not each case is very individual and unique as the history of the engine they are working on.
It is important to firstly understand what is happening to cause a sticking piston.
Pistons get stuck when grit, grease, and especially rust forms to wedge or bond the metal from the metal cylinder wall to the metal of the piston and skirt. Rust, scientifically called oxidation, occurs when oxygen comes in contact with certain metals. It must be noted that not all metals rust. Rusting is most common with ferrous metals such as iron. Over time, the oxygen combines with the metal at an atomic level, forming a new compound called an oxide. Generally, the oxidisation process results in a greatly weakened (powdery) product of lesser technical quality than that of the original metal. If the base metal is iron or steel, the resulting rust is properly called iron oxide. Rusted aluminum would be called aluminum oxide.
Water alone does not cause steel to rust, but acidic and other chemical reactions aid in the attack of vulnerable and exposed metal. Sometimes this rust is accellerated from moisture leaking into the cylinder. Rust can also be accelerated by incorrect shutdown prodeedures where the piston and cylinder are not bathed in protective oil during the final moments of motion. Additionally, the chemical by products associated with combustion will combine with moisture (possibly from heating and cooling of steam layden gases) Remember that water and carbon or carbon dioxide will form carbonic acids, and water with sulphur inpurities in fuels create sulfuric acids. Rust. Sometimes acidification can even occur in the leavings of bugs or animals where an engine has sat in the environment for a long period of time. Ultimately, these engine pistons are big chemical mixing pots with many forms of reaction which over time will form.
What ever has happened within your engine cylinder, what one wishes to do is to get the hardened material loosened or liquified so that the two solid metals can slide over each other and move. Given the chemical nature of this transformation which gives rise to mechanical lock, there are a few ways to unstick a piston. Such can be achieved with heat, pressure, and chemical reactivity.
Heat
Use of torches, and propane burners and ovens to expand the metal and release the mechanical lock. Be especially aware of heating Flywheels!! If done improperly they can crack and shatter. Some guys throw the whole engine into a fire pit and build a fire. Some pack hot coals around it. When doing this you need to be sure that the heat is even, that the heat is not so hot to destroy pot and tin base metals, (take as much apart as you can) and that you have stripped off anything which might not like the process (wires, magnetos, paint do not survive this). If you value any original paint on the engine, you may be in for at tough time as it wont be there at the end. You also want to really watch anywhere that could be prone to the forces of expansion and contraction so that the you arent greeted by the popping of an exploding engine.
Pressure
One of the common suggestions it to replace the head with a piece of steel that one then uses air, water, or grease to presurize the cylinder and force the piston out the back. These are all valuable methods of mechanical force to get that piston moving. A little more complicated and time consuming than the usual method of pounding a piece of wood, this method can be dangerous if you havent planned it out. There are a few stories of people shooting the piston across the room. Remember pressure can be dangerous. There are also a few stories where the mechanical lock was so great and the engine so fragile where the pressure blew the side out of the cylinder wall from a hairline crack. Thus and again it is important that you have completely checked out the condition of your engine.
Pounding wood is the most common method. Using a 4 x 4 of wood is most important to not damge the metal. Direct metal to metal contac can mushroom parts and fracture the steel, and it not reccomended. Again, plan where and how you are striking it. Make sure you dont stress any parts which may not want to be stressed.
Water
There are some that believe that if you turn the engine upright so that water can work its way into the rust and liquify the layer which causes the mechanical lock, then you can free the system. Hot water from a steam system or from a pressure washer can help as well.
Chemical
Each person has their own chemical soup that the pour into engines. This is the basis for many of the liquid wrench products on the market today. The idea is that aromatic and ultra thin oils will saturate and permiate the rust and ease the mechanical lock. Some recipies have diesel fuel, ATF (automatic transmission fluid), and turpintines. What every you use, make sure that the fumes are not such that your workshop explodes sponetaneously. That would be bad.
Electrolisis
Some people will create a vat of water with some form of electrolite and use either a car batterie or some other form of direct current source (usually about 12 volts) to strip away the outter layers of rust. (I have tried this for stuck parts and it works well, just never tried a piston)
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Honing & piston cylinder
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