RE: ringed engine break in?
OK folks, a little clarification, pointing to earlier posts, and general carping.
Please note the following is ONLY for ringed engines.
I’ll start with glazing. There is “Real” glazing, and it is indeed as skiman762 says, caused by oil breakdown from excess heat. But this heat can easily be local, confined to the point of contact between the ring and cylinder wall. The rest of the engine can still be relatively cold.
There are other conditions that are usually called glazing but are not. As an example, an engine with high time can have the walls polished to the point that a new ring wont seat. When new are installed the cylinder wall has to be scuffed to make the new ring seat. We generally call this “Breaking the glaze” even though it’s not a true glaze.
Then we have a near new engine that has been run in with a low throttle setting and an excess of oil. The result here is that the ring polishes the cylinder wall without itself wearing to match. Then when the engine goes into service, running at higher throttle settings, the cylinder pressure comes up forcing the ring more firmly into the cylinder wall. Finally, the ring starts to seat. And since the wall is already polished, this seating can take several hours running time.
So, repeating myself, with the engine on a stand for initial running, peak the high speed needle immediately, then drop the throttle to a high idle or mid range speed for 15-20 seconds. Next go back to high rpm for 5 seconds or so, then back down. Do this repeatedly for about five minutes, then strap it in a plane and go fly. Keep it 400-500 rpm rich on the top end for a while, after an hour or so you can go higher and start leaning the low speed.
What this does on initial running is force the ring into the wall, then before heat has a chance to build drop the speed and let everything oil up again. You get the ring to seat quickly and safely.
Some engines I’ve put together have had less than 30 seconds break in before going to the drag strip. At the same time, those engines seldom ran more than five minutes total time between overhauls.
Now the carping. At least 1/3 of the posts in this thread add nothing at all, others are merely repeating themselves.
Bill.