REFLECTOR: Lycoming IO 360 C1C Valve Problem Question

Wed May 16 00:32:14 CDT 2007

Thanks for the reply. I checked out the reference, thanks for the link. 
I was looking for detail on your #3. All I found was "Remove hydraulic 
lifter and clean free of all oil, inspect for any malfunction." I 
couldn't figure out how to inspect for malfunction. It was definitely 
malfunctioning, I just don't know why.

.... continuation of yesterday's venture....

Today the rocker assembly was removed and sure enough the valve popped 
right up. A compression check revealed a fine healthy seal. So this 
clearly puts the problem at the hydraulic lifter. So inside we must go.

BTW (in the event this is ever used by Velocity owners w/similar 
engines):  The #4 cyl push rod was removable without removing the 
aileron bell cranks although it was close (and your mileage may vary).

The base push rod tube retaining clips were removed and with a gentle 
forceful rotating of the push rod tube toward the valve assembly (away 
from the crank) it clears the base seal and can be removed.

Using a magnet you should be able to remove push rod socket. I used a 
piece of safety wire, carefully bound it in the center hole and pulled 
it out. Now there is another part in there. It is the hydraulic tappet 
plunger assembly (part # 78290). I couldn't figure out how to get this 
out. I removed the  shroud tube seal retainer (part #65007) thinking I 
needed the clearance. DO NOT do this, it doesn't have to be removed. 
This is where the magnet came in. Using a carefully place magnet, the 
hydraulic tappet plunger slides right out of what looks like a barrel ( 
it's the hydraulic tappet body part#72877, this part doesn't come out 
without splitting the case).

I understand in general how hydraulic lifters work, but here is where my 
knowledge runs thin. The lifter was definitely overcharged causing it to 
be excessively elongated which ultimately prevented the valve from 
closing. I do not understand how the lifter can stay overcharged. It 
seems it should slowly leak down. I pressed pretty hard on the lower 
valve of the tappet assembly but could not get it to discharge the oil 
inside. Finally I used my fingers to compress the spring which allowed 
me to move the piston in hydraulic tappet assembly. This allowed the oil 
captivated inside to escape. Then the piston could be removed and 
everything looked normal inside. No foreign matter was observed during 
the disassembly. The hydraulic tappet valve was then verified to be 
operational by blowing through it. It was difficult at first until all 
the thick oil was purged. Air would pass into the Hydraulic tappet 
chamber, but would not pass from the chamber to the outside, so the ball 
valve seemed to be working properly..... unless it's supposed to 
leak....  Re-assembly looks like it ought to work fine.

So here is what I DON'T UNDERSTAND...
What will keep the hydraulic tappet plunger (Hydraulic lifter) from over 
charging again? Why did it overcharge in the first place? Isn't it 
supposed to leak a little bit so that overcharging is remedied 
automatically during normal operation?

Can anyone explain the design of the things?

What's next....
I think a new lifter should be ordered. I think this one will work fine, 
but I don't want to tear this down again and I can't figure out why it 
is malfunctioning. Also the new one can be used for comparison although 
I don't expect to see anything obvious.

Joel

Scott Derrick wrote:
> 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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>>   
>>     
>
>   

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