During an annual inspection we had one cylinder give a ’20/80′ on compression.  After pulling the cylinder that was leaking past the exhaust valve, we ground the valve seats to get them both (intake and exhaust firmly reseated.

The small valve is the exhaust valve and notice the nice shiny ring on the valve face on each valve.

Now let us look at the seats themselves.  The small one is the exhaust and notice the one dark spot at about 1 o’clock on the valve seat.  This was removed with the next step of valve lapping.

The intake valve was also done since it had some small pits in the face.  After all, while we are this far into the process.

Now that they have been lapped and then cleaned (it is very important NOT to let ANY of the lapping Carborundum remain on the valves since this stuff will eat a cylinder in a heartbeat.

Finally, the cylinder will be put back together and reinstalled back on the engine and the compression checked again.

The exhaust valve guide was worn but well within limits and not letting any heat or oil through yet.  This cylinder is a Lycoming 1450 hours since new cylinder.

As a comparison, here is the inside of a new Lycoming cylinder.

Enjoy!

Roscoe