"Breaking In" Used Engines

In the mail yesterday, I recieved the first used engine that I have ever owned, that is except for some 1/2A stuff. It is a Fox .15 that I mentioned in an earlier post. A question I have for the forum is, what is your procedure when checking out and bench running a used purchase? Not knowing the history of this engine, I am working under the assumption that the engine is not broken in, and am handling it as if it were new. I removed the backplate, inspected it, oiled it up, cleaned the outside, put it on the stand, started it up and I am now running it with new engine breakin procedures. How do you do it?

With 5% to 10% nitro and 25% to 28% all castor oil for lube. Sigs fuel with a little castor, which they sell, added. I run them for two minutes, very rich first 6 minutes. Cool down to the touch on the head in between runs, no muffler, no neighbors. For a prop I use one 1 inch less diameter than usual and low pitch, such as a 7X4 for a .15, 8X4 for a .25. I fly them with 8X5 or 9X4. Slowly each run bring the rpms up to just below the two cycle break, then back to a fairly rich setting. After 20 to 30 minutes of 2 minute runs put it on a plane and fly it 4-2-4 in fairly level flight with an occassional wing over thrown in. If there are no problems and it goes 4-2-4, then fly it as you would normally. Others will have different ways and reasons. I have never broken an engine except in collisions in fast combat.

If it's an iron piston it's ok to treat it as new and "re-break it"..

If it's an ABC setup you gotta take care to break it in as ABC setups require.

So, the first thing you gotta be sure of is if it's iron or ABC.

Most used engines have had very little running time. So I regard most of them as if they were new. Couldn't hurt.

Ion, that old engine is not ABC. It's an old Fox .15.

Has Fox ever made a .15 that was not iron? All of mine are iron/steel.
None of mine have required a lot of break-in but I have given all of them a iron/steel break-in, that is two minute runs starting rich then lean a couple of clicks after cool down every other run.
I do break-ins on the bench so I can shut them down if they start to sag at any setting.

I have bought a few of the old 15X models and without exception they all had very little run time on them. However I usually do a careful inspection on the rod and wristpin. Some of them were really stuck from years of sitting. It really isn't the best to run a motor if the rod and wrist pin don't move as it then rotates on the end of the piston and can rapidly induce wear.. Dennis