The International Cessna^® 170 Association

Can anyone tell me the reason for the hole in the crankcase where the generator attaches? I am chasing a nagging leak that seems to get worse. I pulled the generator and it is being overhauled.
After I pulled the generator I noticed the hole thru the crankcase and the gasket which has a half moon cutout. It obviously is there for a reason but i can only see it as a leak. This seems to be allowing oil to seep out around the generator where it attaches to the crankcase. The half moon cutout on the gasket allows the hole to not be completely covered.

I wrote extensively about this subject back in 2002 when I fought a generator area leak.

The accessory case in that area has a depression which allows for the tach-drive adapter above (that’s the little triangular portion above the main generator area of the gasket) to drain back to the main area of the crankcase.

Whenever changing this gasket it’s advisable to also change the tach-drive “garlock” seal also. NEVER cut that generator gasket between the two articles because you WILL have an oil leak.

(I’ll post this response and attempt to find the original article/post and put a link in this post... but don’t hold your breath as I’m still trying to figure out how to do that on my new IPad.)

This is the loong original version: (If you do a search you’ll find where I re-capped it in shorter versions.)

http://cessna170.org/forums/viewtopic.p ... +seal#p914

Thanks for the reply. I have been fighting an oil leak around the generator area. I finally pulled the generator and sent it for overhaul. When i got it back the shop said they did not see an o-ring as many have talked about. Thought this would solve the problem but no!

The gasket between the tach generator and generator has been separated when I bought the airplane six years ago. Maybe i have been chasing the wrong thing. I'll pull both off and put a new gasket on.

Thanks
Brad

I chased a leak for weeks that I was sure was coming from the alternator seal. Long story short, it turned out to be the tach drive housing was warped from over-tightening or the three mounting nuts. I trued it up by putting some 420 grit sandpaper on a solid surface and working the housing back and forth until it was completely flat. Worked like a charm and after probably 75 hours it's still dry.

Phase 3.
Took off the generator again and changed the gasket and tach oil seal also. Now its leaking worse. The oil seems to be coming from the generator. Around the entire exterior of the tach generator and generator it is dry. I'm out of ideas. The oil appears to be coming from the generator. I will try to bring it back to the overhaul shop to see if it was put back together wrong. Frustrating as I am hoping to make it to Oshkosh.

Brad

Remember, you are sealing the oil into the engine, not into the generator.
Often seal #14 is installed backwards and the oil just blows past the seal and into the generator. Also 0-ring #13 is found missing.

The same allies to the tack drive seals, often found installed backwards.

Thanks for all the info. I think that I solved my problem. This is the first time that I took the tach drive off. When I checked the seal the first time I didn't catch the fact that the previous person who put the tach seal in set it down in the flange until it bottomed out instead of it being flush! Third time is a charm!

Thanks
Brad