Friday, August 17, 2012

Why O-200 stick exhaust valves

O-200 Exhaust port

I wrote this back in 2003

"Carbon build-up on the guide pushes the valve stem into the guide. If the guide is the original aluminum bronze style the guide quickly wears out. If the guide is a harder ni-resist style then the guide doesn't wear and the valve sticks..."

I also wrote this: 
Warning! At the first signs of valve sticking ground the airplane. Follow the engine manufacturer's instructions for valve sticking.
Valve sticking can cause immediate and catastrophic engine failure. Sticky valves destroy your camshaft, push rods, lifter faces, etc. Solvent treatments are unsuitable in that while they take time to work your engine is being destroyed!

Broken rocker boss caused by stuck valve

A stuck valve as a much more of a safety issue than a worn valve guide. So now the industry has stuck valves on O-200 engines -- something that was very rare before the guide material was changed. Are you, the flying public, OK with this? It doesn't have to be this way. Better to fix the underlying problem so you don't have stuck valves.

Now granted the O-200 (including the C-85, O-300/GO-300) cylinder is a "little troublemaker" and requires more loving and care than cylinders on any other engine model. I used to get the comment: "its only a C-85". Yes, and if it isn't perfect it will bit you in the pocketbook. But it can be made to work without sticking valves. Guide wear to can be reduced to an acceptable rate even with the softer guide -- Heck that was the norm in the 1970's / 1980's.

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