Annual Compression Tests

[mike.smith]

More food for thought...

After doing a compression test cold, I got:
64/80, 64/80, 60/80, 30/80. Yup, 30.

So pulled the head that had the 30/80 reading. The rear (#3) exhaust valve was burned. So I pulled the other head as a precaution. The rear (#1) exhaust valve was also burned, but not as badly. So I decided to replace all 8 valves and have the seats machined.

Today I did a new compression test COLD, and got:
80/80, 79/80, 80/80, 78/80.

So valve status sure can be displayed in a compression test, even cold.

The front valves & heads looked normal, while the rear cylinders showed signs of being too lean. With the front and rear cylinders getting fuel/air from the same intake pipe, how is the front good and the rear bad? I'd really like to know that one. Poor intake manifold path? I checked for leaks at the manifold before I took the head off and found none.

And more food for thought...
http://www.avweb.com/news/savvyaviator/188758-1.html

[nwawingman]

Thanks Mike! That make me feel better. Maybe I do have an issue after all. My rear cylinders also looked like they were running leaner than the front. # 4 looked to be running the most rich. I will let you know how my readings are when I get them reinstalled.

[mike.smith]

Thanks Mike! That make me feel better. Maybe I do have an issue after all. My rear cylinders also looked like they were running leaner than the front. # 4 looked to be running the most rich. I will let you know how my readings are when I get them reinstalled.

Though keep in mind the 64/80 on a cold engine may not be too bad for an engine with time on it. Maybe that would have been 70 or more on a warm engine? I'm new to being an engine guy, so I'm not the best source of information ;) I just wanted to put out there that your mileage may vary between a warm engine or cold, or they might be very similar. So other indicators might also be needed to pinpoint potential problems.

[Bruce593SX]

And more food for thought...
http://www.avweb.com/news/savvyaviator/188758-1.html

Great link Mike!

From listening to Mike Bushe at Oshkosh is where I got my original recommendation about hot vs cold testing... A great read!

[Onex107]

My first compression test cold at 50 hours had all in the 60/80 range except #3 which tested 40/80 and had a noticable hiss in the exhaust. I was advised to "stake" the valve and retest. My A&P friend said that usually doesn't help but it doesn't cost anything to do. I ran the engine and tested hot and got 64/80. I borrowed a bore scope and looked in the cylinder and noticed the piston face was carboned up except for patches around the edge where the shiney alumunum showed through. It's possible a chip of carbon was in the valve seat and staking would have decreased the leak. Take the valve cover off and pop the valve a couple of times.

[tom0nex74]

The last compression check on my Aerovee showed 30/80 on #3.Thought at first it was leaking rings.Then I traced the leak to the intake valves. Re-faced and polished both intake valves on both heads. Good compression now.
The local VW engine guru says "it's always the valves"..................................Tom Ryan 0nex0074
I am experiencing leaning (higher CHTs & EGTs) when pitching the nose up in climb. Does anyone think that the pitch angle of the Aeroinjector could cause a leaner mixture?

[SonexEZ]

I got problems all cylinders are low or no compression on one , can anyone remind me if i add oil to the cyclinder and the pressure comes up is thatrings or valves ?
what i found was the rear exhaust was too tight of an adjustment , making the surface all carboned up but did not burn so i tried to lap it witht he tool and compond but it only whnt up to 45 lbs removed head its going to a shop in Orlando later this week

[Bryan Cotton]

Rings. If the valves are bad oil won't cause them to seal.

[mike.smith]

I am experiencing leaning (higher CHTs & EGTs) when pitching the nose up in climb. Does anyone think that the pitch angle of the Aeroinjector could cause a leaner mixture?

Climbing will naturally cause temperatures to rise simply due to less air flowing over the cylinders. The AeorInjector itself would not be the cause of leaning in a climb. But lack of fuel flow could. Did you do a flow test with the airplane on the ground in a climb attitude? In a gravity feed system the fuel path (& resulting head pressure) is critical.

[SonexEZ]

I use the following from Aircraft Tool Supply. Works great. The adapter fits in the Aerovee plugs.

2E DIFFERENTIAL CYLINDER PRESSURE TESTER (18MM) 1 $69.95 $69.95
12MM ADAPTER, 2E PRESSURE TESTER 1 $8.95 $8.95

hi I am looking for the 12 MM adapter dont see it on the web page do you have a P/N?