Aerobatic Breather Mod

[PA1195]

Here's from the old Harley Davidson quote from service to unhappy owner..."They all do it"

Some worse than others apparently, the oil blowby that is. Some's unavoidable and acceptable per the article above, but some engines never get run hard enough to create adequate BMEP to seat the rings. That assumes proper ring end gap spacing, end gap clearance, and cylinder round-taper-hone. Then the owner puts on a flat climb prop and gets all worried when the engine redlines before maximum manifold pressure is achieved so backs off and babies the run-in. Then the rings don't seat to the cylinder walls and a good seal never achieved. Don't use a flat prop for break-in.

John has done lots of overhauls and knows way more about this than I, but my vo-tech schooling 55 yrs ago and experience since has supported running them like their stolen until the rings slam shut then 65-75% power. If they leak then eventually carbon fills the piston lands preventing ring flex and rotation and they will always burn oil and leak combustion gas out the breather.

Continental recommended engine break-in. Percent power is a function of both rpm and manifold pressure so do what it takes to maintain the combination:

http://nebula.wsimg.com/46a570b8f2d9...&alloworigin=1

http://nebula.wsimg.com/f2c5b2316072d14429c524b846306496?AccessKeyId=4F9A3E91CE7CAB506B89&disposition=0&alloworigin=1

Gary

[astjp2]

Lets start another posting if we want to chat about choked bores...

[N96337]

When I was running the test cell, we ran a lot of 1820's at night. Short, individual stacks so you could watch each cylinder seat in. With proper honing, all would be seated within the first 15 minutes. From there out, it was just consumption runs. We came up with a setup that we actually took the rings we were going to use on that particular cylinder, put them on a dummy piston and fastened it to the arm on the automatic hone, then had a "slurry" of grinding compound and STP, that bathed it constantly. We'd give each about 15 minutes of run on that setup, and when you put them on the engine, they'd seat before you ever got up to RPM. It was some pretty interesting stuff!
For anything that's run in on the airframe, I do just as Gary said, high manifold pressure and tape the oil cooler over at least 75%, and run it like it's rented!!!
John

[PA1195]

Good writeup John. I gotta' ask and learn something. What changed coming out the stacks when they seated? Were you running chrome built-up cylinders?

Gary

[N96337]

What changes is your flame color. It goes from orange when it's burning oil, to blue, when it seats. Channel chrome wasn't approved for the 1820's then, but we did get Cermichrome approved and had great luck with it. One of our selling points was that you never had to run mineral oil, as the rings were already seated, so it was one less thing for the operator to have to mess with. Curtiss Wright called for less than 10 pounds of oil burn per hour as a new spec, but we had it down around 1/10 of a pound per hour typically. The Wrights really like to breathe, so the Darton clean kits were a big help.
Plus we always ran a straight steel cylinder on the master rod, as it has a bunch of side load, and I've seen quite a few chromed cylinders come apart from that side load, if they weren't treated just right for hydrogen embrittlement.
John

[PA1195]

Well we learned something of value here John. Exhaust color changes with less oil burn. I guess fire breathing rail drag racers with up exhaust stacks must know this stuff too....racing for the Pink Slips is serious business.

Come to think of it my oil drip stove out in the woods goes from blue to orange flame with not enough air and too much oil.

Gary

[astjp2]

Carbonizing flame, torch does the same thing with a lack of O2