0-320 Cylinder issue

A

alaskacubdriver

Registered User

• Feb 26, 2018

• #1

I have a super cub with an 150hp 0-320 lycoming, lately it has been a little weak. So i did a compression test on it and all cylinders came out 73/80. but when you pull the prop though you can feel that when it is on the compression stroke of the number one cylinder there is almost no back pressure. looking for any advice to what the issue could be.

 

D

DENNY

SPONSOR

• Feb 26, 2018

• #2

How many hours on the engine/cylinder? Is the exhaust valve all milky? What kind of CHT's is that cylinder running? What kind of mags and when was last overhaul? Have you done a inflight mag check at 2400 rpm?
DENNY

 

V

Vlad

Registered User

Utah

• Feb 26, 2018

• #3

It might not be your case but I had a broken ring. A piece of less then an inch worked the landing out and exited via exhaust. O-320 cyl #4 zero compression. Stumbled while airborne

 

Attachments

• 
  Hole in the piston - 1.jpg

  778.8 KB · Views: 196

R

Randyk

FRIEND

Talkeetna Alaska

• Feb 26, 2018

• #4

Curious why all cylinders were exactly the same reading. Gauge???

 

gntw

SPONSOR

Ft. St. John BC Can.

• Feb 26, 2018

• #5

Randyk said:

Curious why all cylinders were exactly the same reading. Gauge???

Click to expand...

You can have good leak down but cam will affect compression when pulling through. Pull value cover off watch for movement. Should be about .400 of an in.

 

mike mcs repair

Registered User

chugiak AK

• Feb 26, 2018

• #6

Where was the air leaking when compression test was done? Exhaust or intake or dipstick

 

A

alaskacubdriver

Registered User

• Feb 27, 2018

• #7

The engine only has about 500 since major, but the plane did sit for over a year without being flown.
-there isn’t a cylinder temp gauge in the airplane, so not sure .
-haven’t tried the inflight mag check yet though just ground mag check at 1700

 

A

alaskacubdriver

Registered User

• Feb 27, 2018

• #8

The cylinders all tested from 72/80 to 74/80. I used the compression gauge on a different airplane and it tested correctly.
- puller rocket box cover and both valve springs move when prop is rotated through.

 

skywagon8a

MEMBER

SE Mass MA6

• Feb 28, 2018

• #9

Fly it at full power for an hour and check it again.

 

mike mcs repair

Registered User

chugiak AK

• Feb 28, 2018

• #10

mike mcs repair said:

Where was the air leaking when compression test was done? Exhaust or intake or dipstick

Click to expand...

you still have not provided this info... basic