Front oil sump plug

[n3833v]

My inspector tells me that the front sump plug should be removed about every 2 oil changes to check for contamination. I would like to know what you do in the 170 verses the 172 due to the angle of the pan and oil draining to the rear of the main sump?

John

[cessna170bdriver]

I'm not sure if it's the geometry of the carburetor intake tee cast into the sump, or just that theres a low spot around the drain boss, but a small small amount of oil (along with acids, sludge, etc) does get trapped in the fowardmost section of the sump. It's not at all uncommon to have the forward drain boss corrode completely through and begin to leak, especially in airplanes that don't get flown regularly enough and long enough.

I've never heard the "every 2 oil changes" interval, but it certainly is a good idea to pull the front plug occasionally and make sure that area is cleaned out.

Miles

[GAHorn]

With the natural angle of the taildragger installation of this engine, there is the possibility of a small area immediately AFT of the forward drain plug which does not completely drain during oil changes...EVEN if you do drain the forward plug. Inspection of that area for corrosion is a good idea during annual inspections.
The sump is made of magnesium and since the area that doesn't adequately drain can contain water/condensation then there is a history of corrosion which can occur in that area, and has been known to develop leaks. While I've not heard of it failing "in flight" I've heard several stories where it's been discovered on the ground, much to the dismay of the owner. (They were very glad it didn't fail in flight.)
The sumps can be welded by some certified shops such as Ajax Aviation Inc., 319 Wolf, San Antonio, TX 78216. 800-531-7212 or 210-342-9494

[cessna170bdriver]

George,

Would it be worth the trouble to elevate the tail for those times when you want to make sure this area drains? Or if trapped oil is immediately aft of the plug, maybe suction out this area somehow?

Miles

[GAHorn]

Well, all I can say is: The FAA informed me during my check last Friday that their guideline for inspection of any item is "Cleanliness, Correct-Function, and Security".