Low compression questions

[Mike Kimball]

I started my first annual inspection recently. I performed a differential
compression check on all cylinders and found an interesting thing and a
worrisome thing.

Interesting thing: On 7 cylinders I was getting only high 50s to low 60s
(over 80). It is my believe (for various reasons, not the least of which is
how well the engine is running) that these cylinders are all fine. I can't
figure out why the readings are so low. I can hear leaking air which I
believe is leaking into the case, not the intake or exhaust, i.e., past the
rings. As I'm sure everyone is aware, we like to see numbers above 70 and
all cylinders fairly close in readings. There is only about a dozen hours
of run time since it was rebuilt so far but I would have thought the rings
would have been set in by that amount of time. There's a little less than 6
hours in flight so the engine has seen continuous high power settings as
well.

Cylinder number 8 is only giving me about 32/80 and there's noticable
leaking air sounds through the exhaust pipe. Damn. Apparently, the exhaust
valve is not sealing. I wiggled the rocker and it's loose at TDC for the
measurement. I don't know enough about the characteristics of breaking in a
new engine so I thought I'd ping you guys on the list that do know. Is
there any chance that #8 will simply improve with more run time? Am I
looking at pulling that head so the valve can be lapped in or replaced?
(Man, I hope not.) The engine is running so well, it's tempting to just
call it a 7 cylinder engine and take the horsepower loss. My patience with
drawbacks is getting very thin.

Mike
044SR




-----------------------------------------------------------------
List archives located at: https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe: rebel-builders-unsubscribe@dcsol.com
List administrator: mike.davis@dcsol.com
-----------------------------------------------------------------