REFLECTOR: Lycoming IO 360 C1C Valve Problem Question

[Scott Derrick]

Joel,

What your describing can be caused by

1.) burnt exhaust valve/seat
    After you have verified the rocker is coming up and releasing the 
valve you can check for this.   If the valve is seated and its still 
wheezing when you pull it through this is most likely the case.  A 
borascope can verify it is burned before pulling the cylinder
  
2.) stuck open exhaust valve(coked up)
      If the valve doesn't close, and there is a gap under the rocker 
arm,  something  is preventing  it from closing.  Usually gunk on the 
guide and stem.  This kind of thing almost always gets better as the 
engine warms up.  Commonly called morning  sickness.   This can come and 
go and be seasonal.   Its more common in Lycomings and there are a 
couple of approved oil additives that help this a lot. Changing the oil 
more frequently helps  prevent this also.

3.) lifter stuck open
    If the rocker is not coming up far enough to release the valve the 
valve will leak.   This can be a galled lifter that is getting stuck in 
its hole in the case,  or something has gone wrong inside the lifter 
causing it to ever extend.
   
Here's Lycoming's Service instruction for a sticking valve.  
http://www.lycoming.textron.com/support/publications/service-instructions/pdfs/SI1425a.pdf

This procedure will address 2.) & 3.) above  Be prepared this is not a 
simple procedure like changing a spark plug.  If your real familiar and 
comfortable with engines go for it. If  not get somebody with experience 
to help or supervise.  You can get a good(everythings relative!) look at 
the valve while doing this to verify its not a burnt valve.

Scott

Joel Smith wrote:
> If you have experience/knowledge in this area, I would appreciate any 
> ideas you have to offer.
>
> Problem:
> Cylinder #4 fails static compression test.   0/80#
>
> Symptoms:
> Engine warm up for a few minutes result in the compression test passing 
> with good numbers. Engine usually starts rough and smooths out. We think 
> it smooths as the valve gets happy.
>
>
> Analysis:
> Compression test cold reveals a very audible leak out the exhaust port. 
> I dropped the exhaust stack to check the valve stem for build up that 
> might be jamming in the valve guide. The valve cover was also removed 
> for additional inspection. What I found is that the rocker arm is not 
> being released to allow the valve to close. I can spin the valve with my 
> finger (through the exhaust port) through a full 720 degree cycle. So I 
> know the valve isn't closing. It should not spin when the valve is 
> released onto the face. I tried to insert a .003" feeler gage in the 
> tappet area, and as expected, to tight. I have not removed the rocker 
> arm assembly yet to verify that I can get valve closure (got a bunch of 
> stuff to remove... that's next).
>
> As I understand it, this engine has hydraulic lifters. The only thing 
> that I can think of that would cause this is a stuck lifter (some 
> how...), maybe a push rod being to long (however it gets longer with a 
> warm up, not shorter....)....
>
> Any ideas?
>
> Additional Info:
> Engine has less that 100 hrs since rebuild.
>
> Thanks,
> Joel
>
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