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How to Break-In a Model Airplane Engine

May 05, 2015

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Airfield Models ( In a Model Aircraft Engine

All engines need a break in period.  The procedures for breaking in an engine have been well-documented so I will not repeat all that here.  Every engine I have ever owned came with good break-in instructions.  They just need to be followed.

The break-in period for newer engines is not nearly as long as it used to be, but it is still necessary.  You can either break your engine in on the aircraft or on a test stand or a little of both which is what I do.


Engine Test Stands

PSP Engine Test Stand mounted to a Craftsman Tool StandUsing an engine test stand for initial engine runs has many benefits:

Adjustments are easier to make because the engine is fully exposed.  If the engine is working on the stand but not when you put it in the aircraft, the needles may need slight tweaking.  If that does not work, you can bet the problem is in the fuel system.

There is either a leak, a kink or some other feed problem.  If you did not know this you could spend hours tinkering with the engine before figuring out that you are working on the wrong thing.

The second benefit of a test stand is that you are not putting unnecessary wear and tear on your model while breaking in the engine.  Running an engine imposes strain on the airframe.

The airframe should be able to handle it  after all it is built for the engine you mounted on it.  But I still do not see any point in subjecting the model to unnecessary stress and covering it with exhaust gunk just so I can break in the engine.

If you do choose to break your engine in on the aircraft, at least put the model on an old table or something and get it out of the dirt.

I have owned a couple test stands and while they were better than nothing at all, I wasn't real pleased with them either.  I finally shelled out some cash for the excellent PSP manufacturing stand shown below.  It is heavy duty, easy to use and should last several lifetimes.

PSP Engine Test StandThe stand came with a throttle linkage and a fuel tank which fits in the cradle to the upper right of the photo.  The stand is adjustable for a wide range of engines designed for beam mounts.

I bought a Craftsman tool stand from Sears for about $40.  A piece of 3/4" particle board was given several coats of clear polyurethane to fuel proof it and then it was bolted to the stand.  The PSP test stand is bolted to the board.  It is a simple set up.

The tool stand is heavy enough for the engines I use but at some point it might be necessary to stake it to the ground or sandbag it if a large, powerful engine was mounted to the stand.

You will have noticeably better success when you use some type of test stand to check out your engine.

The PSP test stand doesn't take backplate-mounted engines.  In their ads they mention they have an adapter available but I haven't seen it.  This is an adapter I made in an afternoon to test a bunch of Cox 1/2A engines I have.  The same idea could be applied for larger engines that are backplate-mounted.

Backplate-Mounted Engine Adapter

Backplate-Mounted Engine Adapter

Backplate-Mounted Engine Adapter

Backplate-Mounted Engine Adapter

Not all my Cox engines have a built-in fuel tank so I made provisions to mount a small tank.

Comments from Clarence Lee

"Regarding engine break-in you are correct in saying the engine should not be given a break-in period in the aircraft but on the bench.  However, contrary to what others have said, bench running break-in is not near as effective as 'in the air' break-in.  It is okay to run a tank or two of fuel through an engine on the bench to familiarize yourself with it is operation, but with the engine running static wear patterns, etc., will be different, operating temperatures different, etc.

A few flights in the air doing big loops, Cuban Eights, etc. where the engine is working will accomplish more in a few flights than an hour of bench time.  I have seen lapped iron piston engines in the old days that were given two or three hours of bench running stick up on a first flight due to the operating temperature increasing under actual load."



Setting Model Aircraft Engine Mixture Controls
Maintaining a Model Aircraft Engine

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Copyright 2003 Paul K. Johnson