Oil Filler cap

[dwdw47]

Hi: I have a friend that is building a plane designed by a farmer 60 years ago.
The engine is from a model T, max speed 75 mph .
The original plans has a sliding cable with a pin that locks the oil filler cap, that is screwed on. He has changed that, not wanting the tube to stick out of the cowling. The change is to use a non threaded plug design with just 2 "o"rings for a friction fit without the cabled pin as a lock. My view is that the filler plug could come out from vibration or just the air going past it, Bernoulli's principle. I have an engineering back round and have used redundant safety wires and cotter pins on many fasteners in the printing industry.

He wants to fly to every state a write a book on his adventure. I just want his experimental plane to make every trip being as safe as humanly possible.

Any advice would be greatly accepted.
Thank You for listening.
dwdw47

[Bob H]

Just in general terms, loosing an oil cap and having all the oil sucked out is bad news. I'd do everything to assure that never happens.

I can't exactly picture the present setup- do you have a pic?
Bob H