REFLECTOR: Lycoming IO 360 C1C Valve Problem Question

Joel Smith joels at austin.rr.com
Wed May 16 22:48:10 CDT 2007


Thanks for your reply, good feedback here. My comments/questions inl ine.

HYTEC45 at aol.com wrote:
> The valve spring/s force will keep the lifter unit from 
> overextending.  The leak-down comes through the clearance between the 
> piston O.D. & bore I.D. of the unit.  Normal oil pressure delivered 
> through the ball check keeps the lifter extended to prevent any valve 
> train clearance.
Good description, this matches with how I expected it to work.
>   Check that you don't have a broken valve spring.
How do you recommend this check be performed? I would think this could 
be done via a visible inspection, even though the inter spring is a bit 
difficult to see (has been visually inspected). I (know how and) realize 
I can remove the springs. Do you think it is necessary?
>   However, even a broken spring should provide enough force after 
> shutdown with hot oil to cause leak down and eliminate over extension, 
> but something to check while your there.  Don't become a car dealer 
> auto mechanic and be a "part changer", try to find the cause before 
> replacing anything.  Regarding a possible "sticking valve", when the 
> rocker pushes the valve open, it is not a direct inline force with the 
> C/L of the valve stem.
This is interesting. I see what you mean by the forces being off center. 
I also observed a very small burr on the edge of the tappet cap. I could 
feel a slight scratching as I slid it in and out of the tappet body. 
There were no ridges. Maybe with off center forces this could bind, 
however the problem at teardown was that the lifter was overextended. 
The burr was removed and now slides smoothly.
>   With a worn or out of spec guide, the slight side force can cause 
> the stem to bind against the I.D. of the guide and stick.  Removing 
> the rocker arm load will allow the stem to re-aline with the guide and 
> everything works good by hand, but the problem is still there.  Check 
> stem to guide clearance per the SB.  A benefit of roller rocker arms 
> are this side load is greatly reduced. 
> TEC 
>
>
>
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