Well, this is non Brit car engine break-in related but Bob Spidell's
description of the proper method of breaking in an aircraft engine
brought this story to mind and I can't seem to restrain myself from
passing it along. Let me just say before I relate it that Bob's
procedure pretty much coincides with my own recollection of the break in
method my dad used. He was both a part time flight instructor and a
licensed airframe and engine mechanic before he retired.
While this didn't involve a car engine I can imagine this happening
during any engine break-in under similar circumstances. This particular
incident occurred quite a number of years ago to a friend of mine. He
had a late 1940s vintage Stinson which was a fabric covered four place
high-wing monoplane with a 6 cylinder air-cooled Franklin engine. The
construction of this engine (and other opposed air-cooled aircraft
engines) was similar to that of an air-cooled VW engine in that the
individual cylinders (jugs) could be unbolted and separated from the
crankcase. During the rebuilding of this engine my friend discovered
that the linings of five of the cylinder were in good enough condition
to just re-honed but that one was scored pretty badly. He had that
liner chromed plated and machined to the correct sized and honed before
reassembling the engine.
To make sure that he followed the proper break-in procedure for this
engine, he call the local Franklin tech rep to get the factory approved
method. He was told to start the engine but not to let it warm up
because this could cause severe overheating in a fresh, unbroken-in
engine. The rep then told him to immediately do a normal take-off (this
is done under full throttle), fly around the pattern once, land and shut
the engine off to let it cool. This procedure was to be repeated some
specified number of times (I've forgotten how many), which was suppose to
achieve good ring seating without overheating the engine.
So my friend pushed his Stinson to the end of the runway, started it up
and did a full throttle take-off without warning up. Everything went
well at first. The engine ran reasonably smoothly and he seemed to have
adequate power. This continued until he got about halfway around the
pattern. At this point he started noticing some engine vibration and
roughness. This continued to get worse until it became so violent that
he was afraid he wouldn't be able to make it back around for a landing.
He throttled back as much as he felt he could and nursed it around for a
landing. Needless to say he was quite shaken by this but once he had
recovered a bit, he began getting concerned about what had happen to
engine. He called up the rep and related what had happened. The rep
had him go over the details of the rebuild to see what he might have
done wrong. When he got to the part about the one chromed jug, there
was this aha! from the rep. What had happened was that the chrome
being much harder than the steel of the other jugs was seating at a
slower rate and that was what had cause the vibrations. My friend
continued the break-in on the ground using the old method of short
running periods until the problem cleared up.
Roland
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