Had to pull a cylinder-Break In?

[sailvi767]

When we did the pre buy on the six I purchased we found 1 cylinder down on compression leaking out the exhaust valve. Flew it a bit and it came back up to normal. At the first annual this year it was down again so we decided to address it. The normal tricks did not work to bring the compression up to where we wanted it. Pulled the cylinder and sent it to Penn Yan where they found the valve seat appeared to have been miss cut probably caused by the cutter chattering a bit. Depending on how the value had rotated explained the up and down compression. Valve seat has been re cut with no other problems noted and cylinder should be back on this Wednesday.
There is lots of info on break in procedures available but very little talks about what to do when one cylinder only is removed. Penn Yann did hone the cylinder. They are ECI Nickel Carbide cylinders that I am told break in very easy. ECI recommends Phillips 20-50 XC oil for break in and normal ops. Any thoughts other then run it hard the first 10 hours? Altitude or airspeed suggestions? The aircraft does have 10 to 1 compression pistons with FI and full engine monitoring.

George

[rocketbob]

I've spent a lot of time researching and understanding how honing is done on aircraft cylinders, both new and in shops, and have come up with better ways to hone cylinders in my own shop. It is absolutely stupid and backward how this is done in the aviation world. Have you ever heard of a non-aircraft engine having to take 20-30 hours to break in? I digress...

Just put X/C oil in it, and follow the ECI breakin procedure, and change oil immediately after doing this and hope for the best.

[Lars]

Originally Posted by rocketbob

I've spent a lot of time researching and understanding how honing is done on aircraft cylinders, both new and in shops, and have come up with better ways to hone cylinders in my own shop. It is absolutely stupid and backward how this is done in the aviation world. Have you ever heard of a non-aircraft engine having to take 20-30 hours to break in? I digress...

Just put X/C oil in it, and follow the ECI breakin procedure, and change oil immediately after doing this and hope for the best.

Bob, I personally would love to read your views on this. I've (re)built lots of automotive and motorcycle engines in the last 40 years or so. And bought a few new cars. Break-in, other than on flat tappet cams on some V8s, has always been a non-issue. I've wondered about this myself. Always interested in learning new stuff, thanks.

[dealfair]

Originally Posted by Lars

Bob, I personally would love to read your views on this. I've (re)built lots of automotive and motorcycle engines in the last 40 years or so. And bought a few new cars. Break-in, other than on flat tappet cams on some V8s, has always been a non-issue. I've wondered about this myself. Always interested in learning new stuff, thanks.

Yea Bob, please share your thoughts.

Regards,

[rocketbob]

Most engine shops have something along the lines of a Sunnen CK10 hone. There is one stone set that is used for aircraft cylinders (Sunnen officially recommends this stone in this application) and its 150 grit aluminum oxide, for both roughing and finishing. With this stone, shops can get the 25-35 Ra (avg. roughness) finish on the hone spec'ed in the OH manual. In aircraft shops there is no difference between roughing and finish honing. They just hone the cylinder, and when the diameter gets to where they want it, they stop.

Meanwhile the rest of the engine building world has evolved. They now use other values beyond Ra; Rvk, Rpk, and Rk (valley depth, peak height, and average). What this has led to is called plateau honing, or I should say, how plateau honing is measured and made repeatable. Nobody finishes with 150 grit, except for guess who, the aircraft shops.

Typically shops that do race engines rough with something like 150 grit, then do a few strokes with 280 grit to plateau, then use a plateau brush in reverse to clean up the torn material in the cylinder, usually 4-5 strokes. I've even had engine guys tell me they plateau with 600 grit stones. Not aircraft engine guys mind you.

Breakin typically occurs in seconds. Valley depth is more carefully controlled by using this process, and so oil retention will be better, compressions improve, oil stays cleaner longer, etc.

[DanBaier]

I'd recommend the following (the condensed version of the Eci recommended procedure) - this cylinder has not had the benefit of running on a test stand - use straight-weight mineral oil:

After installation, short (less than 2 minutes or 300 CHT, whichever comes first) run to determine no leaks. Let it completely cool down.

Another short run to determine you can get takeoff power. Let it completely cool down.

Tow the aircraft the the runway holding environment. After starting, get on the runway promptly and use about 2000 RPM to get to 40 or so, then full takeoff power.

When you've got pattern altitude, come back on the power. How much? You want 75% power for pressure in the cylinder but less than 400 CHT.

With this procedure (being this is a nickel carbide cylinder) the initial ring seating will take place in about 3/10ths of an hour.

Dan

[sailvi767]

Thanks Dan, Where the Aircraft is positioned makes a quick takeoff easy. Hopefully get it back in the air tomorrow or Wednesday. I have missed it!!!

George

[JonJay]

As suggested, follow the break in procedures recommended by the manufacturer. I recently replaced a cylinder in my Aerosport Power IO360 for an exhaust valve sticking issue. They prefer going back to straight mineral oil for 50 hours, just like a new engine.
The cylinder broke in as expected and you could follow the CHT trend. I ran hard (75%+) and rich (150d + ROP) for 5 hours then resumed normal operation. I think 5 hours is overkill but I wasn't taking any chances. 50 hours is probably overkill too, but I am sticking with it.
The one trend you will not see is oil consumption changes since it is only one cylinder, those changes are subtle.