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Lycoming O-360 (A4K) - March 2, 2005

I've got a 1979 Beech Sundowner with a 180 hp Lycoming O360 A4K engine and a 10-5219 carb.  Engine has about 900 SMOH.  When I first start up a cold engine it runs rough for about 10 to 20 seconds then smoothes out.  At idle taxi (about 1,000 rpm) I think I hear the engine making a "popping" sound.  Run up is normal.  Max static run-up is normal.  Climb, cruise seem normal.  Any idea why I might have the two symptoms?

F.R.  Lake Worth, FL


Reply from Roger,

     This is a classic example of sticky valve(s).  For starters check out Lycoming Service Bulletin 388C which partially deals with the issue.  Lycoming recommends a valve stem to guide clearance inspection every 400 hours.  You indicate that yours has 900 hours since overhaul.  Unfortunately, the Service Bulletin only deals with exhaust valves, but from experience we have found more intake valves tight than exhaust valves.  Recommend both intake and exhaust springs be removed and the valves checked for slight perceptible clearance between stems and guides.  If the clearances are tight you can push the valves one at a time into cylinder and ream the guides to the manufacturer's recommended dimension.  If valve stems are loaded with carbon,  you can pull them through the spark plug hole and polish them one at a time.  An experienced individual with proper tools can complete the project in about 1.5 hours per cylinder.  If the valve springs are more than 15 years old replace them all.  Replacing the springs will help prevent the valves from sticking.  

Roger


Sent: Wednesday, January 31, 2007 10:53 AM
Subject: Re: 1200 TBO

Is the Lycoming 180hp 0-360-A4K a candidate for a 1200 TBO or is it one that has the1/2 exhaust valve stem diameters and good for 2000hr TBO?  This engine is on a 1978 Beechcraft Sundowner and is 1305 hrs SNEW.... [ Original Engine of The Aircraft ] Thanks in advance Jack


Hi Jack,

Thanks for your question.  The TBO is 2000 hours for this particular engine.  Service Instruction 1136A dates back to Dec. 15 1967.  This engine does have the 1/2 exhaust valve stems.  However, Lycoming does recommend that the engine be "overhauled in the twelfth year" see http://www.lycoming.textroncom/support/publications/maintenancePublications/serviceInstructions/SI1009AS.pdf  .  In reality, the engines are often overhauled at 20 to 25 years, if they do not reach TBO.  Unless the engine has had a cam replacement or engine teardown, I would recommend replacing this engine with an overhauled or remanufactured engine at this time.  Lycoming engines often have cam failures due to inactivity.  Roger

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