On Sat, 6 Dec 2008 21:55:55 -0600 "Mark Langford" <n5...@hiwaay.net> writes: > Anybody been making progress on a KR lately? The weather's been less > than optimal lately for flying OR working on KRs here, but surely > somewhere somebody's getting a little closer to flying. I'll bet > the Aussies are cookin'... > > Mark Langford, Huntsville, AL
I don't know if what I've been doing would be considered progress or regression. I pulled the top end off my O-200 to replace the worn out valve guides that we didn't replace when I originally built this engine. We'll just chalk that up to my learning curve. This has turned into a lesson in why it's a good idea to tear down an experimental engine for inspection no matter how small the risk of the experiment. This engine was an experiment using the C-85 pistons in place of the O-200 pistons, which I had heard was a simple to do, accepted practice. When building this engine up 6 years ago, I discovered that the pistons hit the bottom of the spark plug bosses inside the cylinders. I had ground the bottom off the spark plug bosses to clearance the pistons and have flown it like that for the last 360 hours. Upon tear down, I discovered some abnormal wear on the bottom side of top compression rings where they ride in the piston. It turns out that the top ring was actually going slightly beyond the top of the steel bore and was hitting the aluminum in the head causing the ring to twist, creating the strange wear in the bottom side of the ring. This would have eventually cause a premature failure of the ring, piston or cylinder. We figured we could remedy this by doing a precision hone job a few thousandths beyond the top of the bore into the head as the ring wasn't going completely off the steel bore. Upon reassembly last weekend, I found that the top ring in one cylinder was now springing out into the head and binding up. The only solution was to order a set of stock O-200 pistons and downgrade the engine to a stock O-200. :o( When I pulled off the old exhaust, I was horrified at the bad things I had done to the flow inside the exhaust when I built it. I still remember that my mind set 12 years ago was to get an exhaust on this engine and get it flying. I had committed to myself that I would build a new exhaust a few years ago and figured this would be a good opportunity to do so. Now I have completed building a new exhaust of 4 seperate header pipes that should significantly improve the breathing of this engine. I figure that if I did a really good job on the exhaust, the engine might breath well enough to offset the loss of HP due to downgrading the compression of the engine. Lots of time and effort and about the best I can hope for is the same performance as I had before I started. Of course now the engine shouldn't have a future failure somewhere in the offing, and it shouldn't push oil overboard anymore. Oh yes. I also saw evidence on all four pistons that this engine had been suffering from some detonation as well. It wasn't significant enough to ever cause a failure, but the evidence was there. It may have been due to the slightly advanced ignition timing I was running in combination with the higher compression pistons. I really doubt that it would have had any problems at the altitudes I normally fly, but was probably not a very happy engine while I was zooming around at Mt Vernon. I'll try to get some pictures together and post them to my web page sometime in the next couple of weeks. I'm probably still about a week away from getting the plane back together and the condition inspection completed so I can get back to flying again. Jeff Scott Los Alamos, NM N1213W ____________________________________________________________ Take a break - you deserve it. Click here to find a great vacation. http://thirdpartyoffers.juno.com/TGL2141/fc/PnY6rw2gGUzhPdfIJFJjVBe9uOwLcyWv4KfbanKVOtlSlbiYNJAqs/
