The International Cessna 170 Association

There have been multiple posts over the years regarding the issues we can have with our magnesium oil sumps and the corrosion that can ruin them. I decided to remove the oil cooling shroud and pull the front sump plug to see what I'd find. I expected to see quite a bit of oil to drain out when the plug was removed. Didn't happen. NO liquid came out. There was some minor accumulation of gunk on the plug and I got a little on the end of a Q-tip. Inspected the sump as best I could with a borescope and could not find evidence of any corrosion. Hopefully what I saw was indeed a lack of any. I have often wondered if it would be advisable to put a quick drain in that forward plug location so any accumulation of oil, etc. could be removed at oil changes. I've not heard of anyone doing so.

Frank, not much doing good by pulling that plug. The surface condition of the sump, forward of the carb area and aft of the internal boss of the drain plug could only be determined after the sludge boundary layer has been removed. That’s fairly impossible with the sump installed.

Thanks Jim. Thought of flushing the forward area with mineral spirits in order to get a better view, but decided not to do so.
Anyone recall what the company in Kelowna was charging to coat usable dumps? Just hope I don’t have a need to use their services.

Frank-
Here is a picture of typical front drain plug corrosion. This gives a good idea where you can look with your borescope if you can get the pan cleaned up enough.

I have also seen corrosion between those two carb stud bulges where they form a trap.

The folks in Kelowna won’t repair any case that has been weld repaired previously or if the case is penetrated. I don't know what they charge but I would use them first, before a weld repair attempt. You could always try a weld repair later if Kelowna rejects it.

Click on picture to enlarge it, and then you can manually enlarge it more for more detail.

Cleo Bickford recommended using a Phillps #2 screwdriver and, with your hand only, strongly attempt to poke a hole thru the sump immediately aft of the fwd drain plug at each annual. If you break thru... you may have just saved yourself, your engine, and your airplane.
This recommendation was his during a conversation in which a Member mentioned his sump having a mysterious oil seepage just aft of that plug. While I don't recall the Members name... I do recall that his sump was indeed corroded to the point of imminent failure and that's how they found out.

15 years ago ,yes 15 years a owner had a leaky sump [cessna 172] and did a bush repair himself in the northern part of Canada. The sump was removed and sand blasted the corrosion area ,then a hole was drilled through the sump to accept a AN3 bolt and then A4 metal set was placed in this area and 2 penny washers and a AN3 bolt was used to secured the penny washers in a sandwich situation. It had gone through at least 16 100hrly inspections and no one picked it up. It was only picked up,when doing a conversion to a Lycoming O-360 . When asking the owner about it said “he forgot about it”. The hours on the aircraft were very shakey and some of the 100hrly done ,were done with a pencil also.

When I asked the folks in Kelowna back in 2006 about the reliability of their epoxy coating repair process before allowing them to repair my corroded sump, they told me they had O-300 engines coming back for inspection and return to service after their third TBO that did not require touch-up. That service life is good enough for me.