[Jim P]

For the engine guru's...

I just did a compression check and #3 is down a little, 72/80 instead of the normal 78/80. Ending is an XP-360/CS/ injected, with 305 hours. The #3 bottom plug is pretty oily and the top plug looks good, and in flight and on ground run-up, mag checks are good. I took the following data today before compression check, gapped, and cleaned plugs, and adjusted timing and it looks like #3 is acting up a little (#3 didn't change after cleaning/ gapping). My thinking is to start with the plug and work back up the ignition chain..

Other thougths? #3 is the top series in the bottom group of 4 (the squizzly one).

 

[PCHunt]

Where's the leak?

Hi Jim-

I had a similar occurrance on an O-320-E2D. One cylinder down just a bit. When you are performing the leak test, where is the leak?

If you have a leaky exhaust valve, the hiss will be evident at the exhaust pipe.
If you have a leaky intake valve, the hiss will be evident at the carburetor, or injector throttle body.
If you have leaky rings, the hiss will be evident at the crankcase breather exit.

In my case, cyls 1, 2, and 4 tested at 77, while #3 was 72, within limits. But there was a hiss at the exhaust pipe.

There was a worn valve guide in the exhaust valve of #3. Pulled the cylinder, took it to a shop, and $125 later, no leak, and compression was 76.

The best way to listen is to use a short piece of small diameter hose, and put one end in/near your ear, and the other end near the exhaust, intake, and crankcase breather.

If it is the rings leaking, fly the plane a few more hours, at high manifold pressures, and retest. If the exhaust or intake valve is leaking, investigate further, with borescope if possible.

The oily plug suggests the possibility of a worn valve guide. Hope this helps.

BTW, I am not, and never have been an engine guru, or any other kind of guru!!

 

[osxuser]

Good advice all around, although it's possible it could just be carbon on the valves too, in which case you can lap the valve in place, without having to pull the cylinder.

 

[Jim P]

Next steps

In talking with Bart at AeroSport, he suggested swapping plugs (and check resistance on current plug), which I'll do tomorrow, fly it a couple hours, take some data, look at the plug and do a compression check. If that doesn't do it, I'll run it down to the shop and we'll take a look at the valves and see where we go.

 

[Jim P]

Update

OK, the #3 squiggly data line was a red herring, the #3 EGT probe was going, which follows my #4 a month ago. So.... swapped plugs, flew 2.2 hrs, and the new plug was also really oily, not gas, but oil. Did another compression check on that cylinder and it was up to 74, with the leak coming out the breather, and not intake or exhaust valve. Somehow, I'm blowing a lot of oil past the rings.

 

[Radomir]

Jim, did you get a chance to boroscope it? Could possibly be a broken ring?? How does the barrel look inside?

 

[osxuser]

Jim, did you get a chance to boroscope it? Could possibly be a broken ring?? How does the barrel look inside?

Honestly, at 72-74 through the rings, you have nothing to worry about. Keep the plugs cleaned every 50 hours and rotate them per Champion. It's pretty typical for that to happen on #3 around 300 hours, so I wouldn't worry too much.