Storing an idle engine can be tricky. Due to things out of your control, an engine could be sitting for a while. How can you ensure your engine avoids corrosion or rust while you wait? Continue reading below for some tips on storing an idle engine!
While I was at EAA AirVenture Oshkosh 2021, I talked to a number of pilots who were planning to buy an engine for their kit plane or restoration project long before the airplane was ready for flight.
There are many reasons to buy ahead. You may get a better price, you can avoid back orders, and it does give you a feeling of being almost done with a project.
But then reality sets in and there are delays due to missing parts, lack of time, etc. All of a sudden, the engine has been sitting for months — or even years — and the question of rust and corrosion comes up.
How can you prevent rust and corrosion in an engine that is just sitting waiting for a homebuilt to be completed or idle for a few months during the winter?
It depends on what kind of engine you have.
While engines from Continental Aerospace Technologies and Lycoming Engines have a lot of similarities, on the subject of corrosion while idle, they are very different.
This is directly related to where the camshaft is in the engine relative to the crankshaft. Since the camshaft is the highest load point, it is the most vulnerable to rust and corrosion.
In Continental engines, the camshaft is located below the crankshaft. Although the cam and lifters do not normally sit in oil, they are very close to the oil and there is kind of a wicking action.
Additionally, the cam and lifters are in the center of the engine, so they are not as subject to temperature changes and condensation formation. The rising and falling of the temperature is what causes condensation to form, which leads to rust.
Chapter 9 of Continental’s Standard Practice Maintenance Manual (M-O) covers the engine preservation procedure suggested by the company. To get access to it, you’ll have to create an account at Continental.aero.
Among the many suggestions in M-O is a recommendation to use a product called Nox Rust, a vapor corrosion inhibitor (VCI) for idle engines. From what I gather, this product is kind of like the old Vapor Phase Inhibitor (VPI) that was used during World War II to protect spare engines being shipped overseas.
Continental also recommends using a preservative oil that meets the Mil C 6529C specification during prolonged storage.
I have also heard of pilots adding a few extra quarts of oil to the sump to cover the cam and lifters to ensure additional protection. If you do this, make sure to drain the extra oil out before starting the engine after its idle period.
The bottom line is over the years I have not seen a lot of rust and corrosion problems with Continental-designed engines.
Lycoming Engines are a slightly different story. The camshaft is located above the crankshaft, away from the oil in the coolest part of the engine. This makes these engines susceptible to water condensation when idle.
Lycoming has a mixture it adds to the oil in engines that are shipped from the factory, but this is only good for a few months. It also has Service Letter L180B and Service Instruction 1534 that cover engine preservation.
These documents also recommend using an oil that meets the Mil C 6529 C specification during storage.
One of the tricks I have heard is if the engine is in a crate, add the preservative oil, then seal up the top of the engine and store the engine upside down so that the cam and lifters are covered with oil.
Other pilots have kept adding oil to the engine during storage to fill the crankcase up to the top.
These methods can get a little messy and care must be taken to ensure that there is not a lot of oil in the cylinders prior to starting.
Another trick I have heard of is to add a heavy-duty diesel engine oil to the crankcase and turn the engine over to circulate the oil throughout the engine. This works well except in engines with copper alloy exhaust valve guides. And you must remember not start the engine on this oil.
All of these tricks have a down side, so I usually do not recommend them.
So what is the best method for preserving a Lycoming engine?
- The best method is to minimize storage time as much as possible.
- Always use a Mil C 6529 C oil for storage.
- If your plane is going to be down for just a few months, change the oil before putting it in storage and add just a few quarts of the preservative oil to your oil change. You can then just fly away on that oil change when you are ready to go again.
- Always store your engine in a controlled climate area. Remember, it’s the rising and falling of the temperature that causes condensation to form, which leads to rust.
- Also, don’t make matters worse: If you are storing your plane for an extended period, do not go out and start the engine thinking it will help to coat all of the parts in oil. When idling, you do not get the oil hot enough to boil the water out, so you just end up creating the perfect conditions for rust and corrosion.