-- "Wayne & Kathy Tokarz" <[email protected]> wrote:
I think the reason that your pistons are overextending into the barrels is
that you have the wrong crankshaft. Check out Harry Fenton's excellent web
site on Continentals.
http://www.bowersflybaby.com/tech/fenton.htm
He explains all the ins and outs of modifying Continentals. At our field we
had a Continental with a mix of parts, C-85, C-90, O-200 and that baby made
around 130hp! Never saw a Luscombe perform so well !
Wayne and Kathy Tokarz
--------------------
I've read his site. Since I bought this genuine Continental O-200 crankshaft
new and have verified the part number, I don't think that's the case. In fact,
the measurement confirms that the top of the top ring goes .015 past the top of
the barrel, so it shouldn't be hanging in the top of the cylinder. However,
take that .015, plus the clearance in the ring land, and the ability for the
ring to twist a little bit, and it clearly does pop out into the head and hang.
It only does so in one cylinder of the 4, but we didn't find anything wrong
with that cylinder and it didn't measure any differently from any of the
others. In fact, I flew this same piston in the same cylinder for 360 hours
before this tear down. The only change was an aggressive precision honing of
the cylinders with a carbide hone to ensure that the barrels were straight and
round. After honing, they all still meet new specs for +.015 sizing. When
honing, we did run the hone up onto the edge of the aluminum in the head to cut
it back enough to match the cylinder bore as the top ring had been hitting the
edge of the aluminum and had caused some abnormal wear on the top rings. What I
suspect is that taking that ridge of aluminum out now allows the ring to run
partially up on to the aluminum and part of the top ring twists out into the
head in the areas where the aluminum doesn't match the bore of the barrel.
At this point in time it's moot as the engine is back together with stock O-200
pistons in it. I have some work to do on the airframe and need to finish the
annual, then should have it back in the air next weekend.
If nothing else, one should take away from the discussion that just because you
read on the internet that something is a standard practice, doesn't necessarily
make it so. While Harry says it can be done, he also is pretty clear about
clearancing issues and recommends buying pistons other than the C-85 piston to
make more compression. He lists at least two sources for high compression
pistons for the O-200.
You can also read what he has to say about pulling the kind of HP claimed above
out of an O-200. From memory I believe he said to expect roughly 100 - 200
hours between tear downs and that he doesn't recommend building an engine like
that for an every day flier. No thanks. Reliability comes way before
performance in my book.
-Jeff Scott
Jeff's first rule of experimental aviation "Everyone lies. Take the difference
between expected results and claimed results and divide by 2 and you'll be in
the realm of reality."
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