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Apparently My post to this subject didn't get to
the list. No big deal tho, since most of my subject matter got here from
others on the list. Couple of points though.
Re-builders nearly always get the cylinder bore taper
wrong. Unless the taper is correct, (tighter at the top) the cylinder will
not be completely the same diametrically, from top to bottom when hot.
This condition will cause premature cylinder wear, uneven heat disbursement ,
cracked cylinders, broken rings, etc. And because of the competition
between the three major suppliers, ie: ECI, Superior ( probably the largest) and
the O.E.M's Continental and Lycoming, the price difference between re-worked and
new is much closer, Making "new" the way to go from all points of
consideration. Also, from the standpoint of re-built engines, the best buy
overall for the long run is a complete cylinder package, available from all
three. The package includes: Cylinders,pistons,valves,valve
springs,guides,keepers,and rotators. You're going to spend between 8 and
12,000.00 to re-build you engine, so why not do it right. In my opinion,
you generally get what you pay for.
Those of us that have other than Continentals, be-ware
of the camshaft, the weak point of Lycoming.
When re-building ALWAYS specify a "new" cam,
not re-ground. Two reasons: The lobs need to be carburized. This is
too costly to do in the field, and is seldom done. A tocco job is the best
you can expect, and is not sufficient, causing a soft cam and premature
failure. Second, Lycoming has never published it's grinding specs. because
they consider it proprietary information. Consequently field re-workers
seldom get the 'Dwell" or "duration" exactly correct, and this is
a critical point to "full power" performance, and long valve
life. The point about heat treating also relates to
Continentals.
There is so much that needs to be discussed here about
re-building, that I don't have time to go into it, and you probably don't want
to read. But re-building an engine regardless of manufacturer, needs to be
done without budget restraints, which I know is a pie-in-the-sky- attitude, but
Lycoming for one, lists over 200 individual parts that should be replaced during
overhaul. I'm willing to bet that a significant percentage of those are
not. Whatever you do, keep cloth shop rags away from your aircraft engines
internal parts. :-)
Ok gang, have at me!! Sorry I got my button
pressed.
Doug
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