The International Cessna 170 Association

So I have a recent overhauled O300d. At the first oil change after Overhaul (at 24.5 hours) we did compression checks all at or above 77/80. We were having some timing issues with the right mag after that oil change only to find out that our right mag had been sent to us with the impulse coupler put on the wrong way. The shop found that issue and buttoned the plane back up. I noticed though that the breather tube was as low as it was before and ever since picking up the plane from that shop it has been spewing oil like no tomorrow. The shop is a fine shop and I don't think they did anything wrong to make that happen other than the breather tube is in a different position which is why I am here. The breather tube stuck below the cowling in the slipstream by 2 inches previously and really had a few drops here and there. Now it is even with the cowling and flowing like no tomorrow. Is there an option to catch that, that is STC'd. Do I have to put one foot out the door and the other hand out the other window to make this not drip like no tomorrow.

It sounds like the tube end is now perfectly placed to form a vacuum in it sucking oil from the breaker. From your description it sounds like the tube was farther into the slip stream and a vacuum was not created. I would normally not have the end of the tube below the cowl or just at the cowl level, but up inside an inch or two thus avoiding the vacuum being created. Why don't you move the tube and see what happens. BTW there should also be a "whistle hole" which is a hole in the side of the tube so the tube is not seals if ice forms blocking the end of the tube. You should check for this hole and make sure it is there.

Until rings are fully seated ..a bit more than normal “blow-by” is to be expected….but after 24+ hr I’d have expected it to stabilize. When performing a compression-test…regardless of actual compression-numbers…..any sounds of air escaping at the oil-filler-cap..??

My guess is you have at least one glazed cylinder. Use the search function here to look up applicable words such as breather tube placement and blow by. Continental’s Service Bullerin M89-9 tells how to determine if your crankcase has excessive pressure.