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Lycoming Crank Plug Failures

Martin Sutter, RV-6 N868CM, 1,300 hrs

New Lycoming engines used with a fixed pitch prop can result in a forced landing or worse if you do not read the fine print!
In August a friend of mine suffered severe injuries and his new RV6 was destroyed in an off-airport emergency landing after oil covered the canopy.  What happened?

My friend installed a new 0-360 in his RV6 together with a fixed pitch prop.  He followed the instructions (or so he thought) provided by Lycoming.  Basically they state:
 

If installing a constant speed propeller, remove the front crankshaft expansion plug.  If a fixed pitcdh prop is used, this plug must remain in place.
At the bottom of the page is a note reading:
 
If the engine is to be converted from fixed pitch to constant speed, or from constant speed to fixed pitch, refer to service instruction #1435.
This document is enclosedin the back of the instructions.

My friend and, as it turns out, many others, simply bolted the prop to the engine as it came out of the crate.  Bad move!  What service instruction #1435 says is that you must remove the front plug, puncutre or remove the rear plug, and reinstall a new front plug to prevent oil pressure from building up behind the front plug.  Failure to do so may result in an oil leak past the front plug.  This leakage can be sudden and significant as in my friends case.

While my friend only had 72 hrs on his engine, another local RV-6 experienced the same mishap afterover 200hrs.  Not being aware of the reason for his problem he simply replaced the front plug only to have a major in-flight leak occur again a few hours later.  Both occurances resulted in forced landings thankfully with no damage.  A check with the salvage center in posession of my friend's wreckage revealed that his was the third homebuit they recieved for this reason.  The local air salvage firm has two!

In summary:  If you have a hollow crankshaft engine and are running a fixed pitch prop, make sure the provisions of service instructions #1435 have been complied with.


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